1. A bearing unit (10) comprising:

-a fixed radial outer ring (31),

-a radially inner ring (33) rotatable about a central axis of rotation (X) of the bearing unit (10), the radially inner ring (33) being provided at its end (33a) with at least two circular sectors (40) separated by at least two grooves (41),

-an array of rolling elements (32) interposed between the radially outer ring (31) and the radially inner ring (33),

-a collar (20) for clamping said radially inner ring (33) on a rotating shaft,

the bearing unit (10) is characterized in that each circular segment (40) comprises a lip (42) having a thickness(s) and a step (43) having a thickness (s + s1), wherein the thickness (s + s1) of the step (43) is greater than the thickness(s) of the lip (42).

2. Bearing unit (10) according to claim 1, characterized in that the ratio between the thickness(s) of the lip (42) and the thickness (h) of the radially inner ring (33) is between 27% and 40%.

3. Bearing unit (10) according to claim 1 or 2, wherein the axial length (a) of the step (43) is 25% to 35% of the axial length (b) of the circular sector (40).

4. Bearing unit (10) according to any of the preceding claims, wherein the incremental thickness (s1) of the step (43) has a value less than or equal to 50% of the value of the thickness(s) of the lip (42).

5. Bearing unit (10) according to any of the preceding claims, characterized in that the number of circular sectors (40) and slots (41) is comprised between 6 and 8 each.

Background

Bearing units provided with rolling elements and systems for clamping the units to a rotating shaft are known.

The bearing units are used to allow relative movement of a component or assembly with respect to another component or assembly. Typically, the bearing unit has a first component, for example a radially inner ring fixed to the first component (e.g. the rotating shaft); and a second component, for example a radially outer ring fixed to the second component (e.g. a stationary housing). Typically, as in the previous examples, the radially inner ring is rotatable and the radially outer ring is fixed, but in many applications the outer element rotates and the inner element is fixed. In any case, in a rolling bearing unit, the rotation of one ring with respect to the other is allowed by a plurality of rolling elements located between the cylindrical surface of one component and the cylindrical surface of the second component, these surfaces being commonly referred to as raceways. The rolling elements may be balls, cylindrical or tapered rollers, needles or similar rolling elements.

Bearing units having a clamping collar for mounting on a rotating shaft are also known. This solution is simpler and more economical than providing a solution for a forced interference coupling of the radially inner ring to the rotating shaft. However, the use of a clamping collar has some drawbacks, since the noise and excessive vibration generated may damage the shaft on which the clamping collar is fitted. To overcome these problems, known solutions consist in shaping the end portion of the radially inner ring with a plurality of circular sectors separated by grooves, in other words with a series of "slotted fingers" on which the clamping collar engages. The greater flexibility of the circular segments helps to bend the segments against the shaft when the locking collar is assembled and clamped.

This solution has not proved to be effective because the thickness of the circular sectors cannot be reduced sufficiently to provide the necessary flexibility, due to the risk of excessively weakening the end portion of the radially inner ring and causing it to break due to excessive clamping.

Other solutions (for example, having a collar with twice the internal diameter, or forming an internal groove in the end portion of the inner ring) also fail to achieve satisfactory results.

Therefore, there is a need to design a bearing unit provided with a clamping collar such that the clamping is reliable in terms of mechanical strength, while making the shaft and the radially inner ring concentric and avoiding the generation of excessive noise and/or vibrations.

Disclosure of Invention

The object of the present invention is to provide a bearing unit comprising a clamping collar which has the feature of making the clamping more efficient and therefore free from the above-mentioned drawbacks.

According to the invention, the radially inner ring is provided with a plurality of circular sectors separated by grooves in the end portion, which is the portion in contact with the clamping collar. These segments comprise lips and are reinforced by thickened terminal edges (hereinafter also referred to as "steps"). The step of each circular segment represents the area where the circular segment will contact the clamping collar. By means of this novel profile, it is possible to impart to the circular segment sufficient mechanical strength to withstand high clamping torques (clamping moments) while at the same time having sufficient flexibility to ensure an accurate, noiseless clamping.

A suitable design of the lip and the end step further improves the present solution.

According to the invention, a bearing unit is manufactured which is provided with a clamping collar and comprises a radially inner ring having the features described above.

Drawings

The invention will now be described with reference to the accompanying drawings which show some non-limiting examples of embodiments of the housing element, in which:

figure 1 shows in a cross-sectional view a bearing unit provided with a clamping collar according to an embodiment of the invention.

FIG. 2 shows the bearing unit of FIG. 1 in an isometric view, without the collar, so that the circular sector of the radially inner ring is visible,

FIG. 3 is a detail of the end of the radially inner ring, showing the lip and the step of the circular sector, an

Fig. 4 is an isometric view of a bearing unit provided with a collar as shown in fig. 1, in which the means for clamping the collar around a circular sector of a radially inner ring are visible.

Detailed Description

Embodiments of a bearing unit according to the invention will now be described, by way of example only, with reference to the above figures.

With particular reference to fig. 1, a bearing unit 10 for the agricultural sector and/or the field of manufacturing (for example, textile, mining, motor vehicle or food industry) can be interposed, for example, between a rotating shaft and a housing element, which does not form part of the present invention, and the bearing unit 10 comprises:

a fixed (/ stationary) (stationary) radially outer ring 31,

a radially inner ring 33 rotatable about a rotational centre axis X of the bearing unit 10,

between the radially outer ring 31 and the radially inner ring 33, in this case the rolling elements 32 are balls,

a cage 34 for housing (/ containing) rolling elements to hold the rolling elements of the row of rolling elements 32 in place,

a collar (collar)20 for clamping the radially inner ring on the shaft.

Throughout the description and claims, terms and expressions indicating positions and orientations such as "radial" and "axial" should be interpreted in relation to the rotational center axis X of the bearing unit 30.

The radially outer ring 31 is provided with a radially outer raceway 31 'and the radially inner ring 33 is provided with a radially inner raceway 33' to allow rolling of the rows of rolling elements 32 interposed between the radially outer ring 31 and the radially inner ring 33. For simplicity of illustration, reference numeral 32 will be applied to both the single ball and the column of balls. Also for simplicity, the term "ball" may be used as an example in this description and the drawings in place of the more general term "rolling element" (and the same reference numbers will also be used).

The bearing unit 10 is further provided with a sealing member 35 for sealing the bearing unit from the external environment. In the following, the sealing member 35 may even more simply be referred to as a seal 35, although this obviously represents the same assembly.

As described above, the clamp collar 20 has a function of clamping the end portion 33a of the radially inner ring 33 to the rotating shaft. According to the invention, and with particular reference to fig. 2 and 3, the radially inner ring 33 is provided, at its end portion 33a, with a plurality of circular sectors 40 separated by grooves 41. There are at least two such segments 40, preferably six to eight such segments 40; thus, the grooves 41 will have the same number.

Each segment 40 includes a lip 42 having a thickness s and is reinforced by a step 43 having a thickness s + s1, where s1 represents the additional thickness (additional thickness) of the step 43 relative to the lip 42. The step 43 of each circular segment 40 represents the area where the circular segment will contact the clamp collar 20. This profile formed on the circular segment 40 makes it easier to meet the need to grip the collar 20 to remain in place during the process of mounting on the shaft. Typically, the clamp collar moves spontaneously and slides over the segment 40 during the installation process.

A first important feature of the design of the circular sector 40 is the thickness s of the lip 42. The thickness s must be small to allow each circular segment 40 to be more flexible. This feature, together with the fact that the material is not hardened but soft, ensures a better locking of the radial inner ring 33, reducing vibrations and allowing a greater power transmission.

For example, the following table shows the thickness s of the lip 42 in relation to the bearing unit dimensions (function):

size of bearing unit	Thickness of the lip s
		205-206	1.6mm
207-208	1.8mm
		209-212	2mm
214	2.5mm
		215-216	2.7mm
218	3.5mm

In general, if h represents the thickness of the radially inner ring 33, the ratio between the thickness s of the lip 42 and the thickness h of the radially inner ring is between 27% and 40%. Values below 27% will reduce the strength of the circular segment 40, especially in applications requiring high clamping torque. Conversely, values of the ratio s/h exceeding 40% would eliminate the desired flexibility of the circular segment 40. This percentage generally increases with increasing size of the bearing unit.

A second important feature of the design of the circular sector 40 is the axial length a of the step 43. Advantageously, this dimension should be between 25% and 35% of the axial length b of the circular sector 40. Values less than 25% will reduce the strength of the step 43 against the clamping action of the collar 20. Conversely, values of ratio a/b in excess of 35% will reduce the axial length of lip 42 and will again adversely affect the flexibility of circular segment 40. Typically, this ratio also increases with increasing size of the bearing unit.

As mentioned above, the thickness of the step 43 consists of the thickness s of the lip 42 plus an amount s 1. This additional thickness s1 represents a parameter that may be adapted to the type of collar 20 used. In other words, the additional thickness s1 of the step 43 is calculated to minimize the number of clamp collars 20 to be used, thereby enabling the same collar 20 to be used with bearing units of slightly different sizes. For example, there may be dimensions that are quite similar to each other but not exactly the same, since the first is expressed in metric units and the second in english units.

Advantageously, the value of the additional thickness s1 of the step 43 should not exceed 50% of the value of the thickness s of the lip 42.

Referring to fig. 4, the collar 20 is clamped around the circular sector 40 by known methods, i.e. using screw means 21, for example a hexagonal socket cap screw of the "torx" type. The collar 20 is also provided with a slot 22 for release (in relief). The collar fitted on top of the radially inner ring 33 (in particular on top of the circular sector 40) locks the radially inner ring 33 of the bearing unit 10 on the shaft in a concentric manner, without causing damage and/or burrs, and provides a 360 ° clamping force on the shaft, minimizing the stroke of its arms 23, 24 to minimize vibrations.

To conclude, this novel profile of the circular sector provides better performance of the clamping system in terms of transmission of power and vibration levels than the prior art. The novel profile of the segment is more flexible, enabling increased closure (closure) of the segment while using the same clamping torque of the screw acting on the collar.

Functionally, the proposed invention makes it possible to obtain a "concentric" solution, with all the resulting benefits, as follows: the shaft and the axis of the bearing unit coincide with each other; the speed and rated limit load are independent of shaft tolerances; constant or alternating rotational directions may be used; the reduced vibration level does not damage the shaft; friction corrosion is reduced; and simplifies assembly speed.

The solution shown also saves production costs, in particular the costs of various heat treatments (cementation), induction hardening (hardening), etc., since the surface to be quench hardened is only reduced to the raceway where the rolling elements are in contact with the radially inner ring.

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 described embodiments are provided by way of example only and are not limiting as to the objects of the invention or its applications or possible configurations. On the contrary, the description given above enables a person skilled in the art to carry out the invention according to at least one example of its configuration, it being understood that numerous variations of the described components may be envisaged without departing from the object of the invention as defined by the appended claims, interpreted literally and/or according to the legal equivalents thereof.