JPH0457891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a preload bearing in which a bearing is attached to a hollow shaft and the radial clearance of the bearing is negative when the bearing is fixed in the axial direction.

Conventionally, for example, bearing devices for main shafts of machine tools,
In order to ensure accurate positioning of the shaft in the radial and axial directions and to suppress shaft vibration,
2. Description of the Related Art Preload bearing devices are known in which a bearing is preloaded for the purpose of increasing the rigidity of the bearing. There are two ways to obtain this fixed position preload: (1) use a combination bearing in which the axial difference between the end faces of the inner ring and outer ring, i.e. the differential width dimension or the axial clearance, is adjusted in advance; (2) use a combination bearing that is tightened; (3) Using a spacer or shim between two bearings whose dimensions are adjusted to give the same clearance; (3) Using bolts, nuts, etc. that can adjust the axial clearance by tightening them.

On the other hand, many rotating shafts use hollow shafts, such as cutting machines, which have operating mechanisms for chucks, tools, etc. inside the main shaft.

The conventional preload bearing device described above has the following drawbacks. In other words, when the bearing device rotates at high speed, the inner ring and hollow shaft expand due to centrifugal force.
On the other hand, the outer ring and housing are stationary and do not expand. Therefore, the radial gap created between the outer ring raceway, the inner ring raceway, and the rolling elements interposed between them, that is, the bearing's radial Clearance decreases. Initially, the negative value of a bearing with a negative radial clearance (preload clearance) becomes even larger, that is, in the case of a preload bearing, the preload amount of the preload clearance further increases. As a result, the amount of preload on the bearing device becomes excessive, leading to an increase in heat generation and frictional moment, or a reduction in fatigue life.

SUMMARY OF THE INVENTION An object of the present invention is to provide a preload bearing device that solves the drawback of conventional preload bearing devices in that the amount of preload increases when rotating at high speed.

As a means for achieving the above object, the present invention makes the coefficient of linear expansion of the hollow shaft smaller than that of the inner ring, outer ring, and housing of the bearing, and prevents the expansion of the hollow shaft, the bearing, and the housing due to the heat generated during high-speed rotation. This was done by focusing on using the difference to reduce the interference between the hollow shaft and the inner ring.

The present invention is a bearing device comprising a hollow shaft, a housing, and a bearing, wherein the bearing is fitted to the hollow shaft with a necessary interference even during high-speed rotation so as not to be movable in the axial direction, and the housing is provided with a shaft. In the preload bearing device, the linear expansion coefficient of the hollow shaft is fixed to the inner ring, the inner ring, the smaller than the linear expansion coefficient of the outer ring and the housing, and as a result,
A difference arises in the amount of expansion between the inner ring and the hollow shaft due to heat generated during high-speed rotation, and by reducing the fitting interference, expansion of the inner ring due to centrifugal force during high-speed rotation is suppressed, and each of the above-mentioned The difference in the coefficient of linear expansion is set to be smaller by the amount by which the radial clearance of the bearing decreases, that is, by the amount of negative clearance (minus clearance) increases due to the expansion of the inner ring due to rotational centrifugal force. This is a preload bearing device characterized by canceling out an increasing amount of preload.

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a preload bearing device of the present invention, with a hollow shaft 10
It consists of a housing 20 and two angular ball bearings 30. Inner ring 31 of angular ball bearing 30
is fitted onto the hollow shaft 10 with the necessary interference even during high speed rotation. On the other hand, the outer ring 32 of the angular ball bearing 30 is fitted into the housing 20. Inner ring 31
A plurality of balls 33 are arranged between and the outer ring 32,
Anguilla contact is made with the raceways of the inner ring 31 and outer ring 32. Two angular ball bearings 30,3
0 between the inner ring spacer 40 and the outer ring spacer 50 in the axial direction.
is interposed. Inner ring spacer 40 and outer ring spacer 5
The axial length of each of the bearings 30 is dimensioned to provide a preload to both bearings 30. Inner ring 31,3
1 and the inner ring spacer 40 are fixed in the axial direction by tightening a bearing nut 70 disposed on the outside of the sleeve 60 between the shoulder 11 of the hollow shaft 10 and a sleeve 60 that loosely fits on the hollow shaft. 32, 32
The outer ring spacer 50 is fixed between the shoulder 21 of the housing 20 and a front cover 80 disposed on the opposite side by screwing the front cover 80 onto the housing 20 with bolts 90. As described above, each part (inner rings 31, 31 and inner ring spacer 40, outer rings 32, 32 and outer ring spacer 50) is fixed with no clearance between them in the axial direction,
The bearing 30 is preloaded in place.

Then, the linear expansion coefficient of the hollow shaft 10 is the inner ring 31,
When the inner ring 31 and the hollow shaft 10 expand due to rotational centrifugal force when the inner ring 31 and the hollow shaft 10 rotate at a higher speed than the linear expansion coefficient of the outer ring 32 and the housing 20, the amount of preload increases.
The difference between the expansion amount of the hollow shaft 10 and the expansion amount of the hollow shaft 10 is offset by a reduction in the fitting interference. Hollow shaft 10 outer diameter 100 mm, inner diameter 50 mm, inner ring 31 inner diameter
In the case of a preload bearing device with a raceway diameter of 100 mm and a raceway diameter of 114 mm, a preferred embodiment is to set the linear expansion coefficient to approximately 6 x 10 ^-6 , and to set the linear expansion coefficients of the inner ring, outer ring, and housing to approximately 12.5 x 10 ^-6 . .

Next, the operation of the above preferred embodiment will be explained using FIG. 2. Each diagram shows the following contents.

(1) Diagram a: Change in the amount of expansion of the inner ring raceway diameter according to the rotational speed when the inner ring and the hollow shaft fit together without interference, that is, when the inner ring rotates independently.

(2) Diagram b: Change in the amount of expansion of the inner diameter of the inner ring depending on the rotational speed when the inner ring and the hollow shaft fit together and have no interference, that is, when the inner ring rotates independently.

(3) Diagram c: Change in the amount of expansion of the outer diameter of the hollow shaft according to the rotational speed when the inner ring and the hollow shaft are fitted with no interference, that is, when the hollow shaft rotates independently.

(4) Diagram d: The wall thickness coefficient (approx.
0.85) (change in the amount of contraction of the inner ring raceway diameter due to a decrease in the fit interference).

(5) Diagram e: From the expansion amount of the inner ring raceway diameter (a) above,
The change in the amount shown in the diagram d above (assuming that the coefficient of linear expansion of each part is the same, and even if the inner ring expands during high-speed rotation, it fits into the hollow shaft with an interference) change in the amount by which the inner ring raceway diameter increases with increasing rotation).

Here, we will consider how the radial clearance increases or decreases when there is a temperature rise at high speed rotation.

First, the diameter of the rolling elements interposed between the inner and outer rings is extremely smaller than that of the inner and outer rings, so expansion of the diameter due to high speed rotation and temperature rise is extremely small. Diameter expansion is extremely small. Therefore, its amount can be ignored. Therefore, the changes in the inner ring raceway diameter (the outer diameter where the rolling elements roll) and the outer ring raceway diameter (the inner diameter where the rolling elements roll) due to high-speed rotation and due to temperature rise are ordered. You should consider it. In other words, the decrease in radial clearance (increase in the amount of preload in the case of preload bearings) depends on the amount of expansion of the inner ring raceway diameter compared to the expansion amount of the outer ring raceway diameter. If the amount of expansion of the inner ring raceway diameter is larger than the amount of expansion of the diameter, there will be a decrease in the radial clearance (increase in the amount of preload).If the amount of expansion of both is approximately equal, the radial clearance (amount of preload) will be There will be no change.

First, we will consider how the raceway diameter of the inner ring and the outer ring change due to the centrifugal force acting on the inner ring and the outer ring due to high-speed rotation.

Change in outer ring raceway diameter (expansion amount) Since the outer ring is stationary, centrifugal force does not work, and there is no expansion in the outer ring raceway diameter.

Changes in the raceway diameter of the inner ring (amount of expansion) Changes in the raceway diameter of the inner ring due to the centrifugal force of high-speed rotation must be considered as two changing factors.

One is the expansion of the raceway diameter of the inner ring due to its own rotation (diagram a), and the other is due to the difference between the expansion of the inner ring itself (diagram b) and the expansion of the hollow shaft itself (diagram c). Expansion or contraction of the inner ring raceway diameter due to changes in the fitting interference between the inner ring inner diameter and the hollow shaft outer diameter (if the fitting interference increases, the inner ring raceway diameter is calculated by multiplying the increase by a wall thickness coefficient of approximately 0.85). If the inner ring expands and the fitting interference decreases, the inner ring raceway diameter will be equal to the wall thickness coefficient approximately equal to the decrease.
There is a contraction for the amount multiplied by 0.85). In this embodiment, the expansion of the inner ring is larger due to the difference in shape and size between the two, and the fitting interference decreases, and this reduction in the fitting interference causes the raceway diameter of the inner ring to contract (diagram d).

Therefore, the amount of expansion of the raceway diameter of the inner ring is the expansion of the inner ring itself (diagram a) minus the contraction of the raceway diameter of the inner ring due to the reduction in interference (diagram d) (diagram e). .

Therefore, since there is no expansion of the outer ring, the amount of decrease in the radial clearance (the amount of increase in preload)

Next, we will consider how the raceway diameter of the inner ring and the raceway diameter of the outer ring change (temperature change) only due to temperature rise.

Change in outer ring raceway diameter (expansion amount) Since the housing and outer ring have the same coefficient of linear expansion, the outer ring is not hindered by the inner diameter of the housing, and the amount of expansion (A) in the outer ring raceway diameter corresponds to the temperature rise.

Change in inner ring raceway diameter (expansion amount) As in the previous section, two changing factors must be considered.

One is the amount of expansion (B) due to the rise in temperature of the inner ring itself. The other is expansion or contraction of the inner ring raceway diameter due to a change in the fit between the inner diameter of the inner ring and the outer diameter of the hollow shaft due to the difference between the expansion of the inner ring itself and the expansion of the hollow shaft. In this embodiment, since the linear expansion coefficient of the hollow shaft is smaller than that of the inner ring, the fitting interference is reduced. As a result, the shrinkage amount (C) due to the reduction in the fit interference of the raceway diameter of the inner ring diameter is approximately 0.85 by the wall thickness coefficient.
It is multiplied by .

Therefore, the expansion amount (D) of the raceway diameter of the inner ring is calculated by subtracting the contraction amount (C) due to the reduction in the fit interference from the expansion amount (B) due to the temperature rise of the inner ring itself (B).
-C).

Therefore, the amount of change (increase amount: decrease in preload amount in the case of preload bearings) Y in the radial clearance due to temperature rise is calculated from the amount of expansion of the outer ring raceway diameter (A) to the amount of expansion of the inner ring raceway diameter (A). D, that is, B−C).

Here, since there is not much difference in diameter between the outer ring raceway diameter and the inner ring raceway diameter, and the thermal expansion coefficients are the same, the amounts of expansion A and B due to temperature rise of both diameters are almost equal. Considering this, the influence of both on the change in radial clearance is such that they cancel each other out. Therefore, it can be considered that the amount of change Y in the radial clearance due to the rise in temperature is almost solely contributed by the amount of contraction (C) in the raceway diameter of the inner ring due to the reduction in the fitting interference. That is, the amount of change Y in the radial clearance due to temperature rise is the amount (C) by which the radial clearance increases (in the case of a preload bearing, the amount of preload decreases).

Furthermore, we will consider how the radial clearance changes in the case of high speed rotation and temperature rise.

Since this state is a state in which the above conditions occur at the same time, it can be considered that the change in the radial clearance is caused by the state described above occurring at the same time, rather than the state before rotation and where the temperature has not yet increased.

Therefore, the amount of change (increase, decrease) in radial clearance
is the sum of the amount of decrease (amount of increase in preload) X in the above-mentioned state and the amount of increase (amount of decrease in preload) Y in the above-mentioned state.

Therefore, the coefficient of linear expansion of the hollow shaft is determined for the inner ring, outer ring,
The setting value is set to be smaller than that of the housing, and the set value is set such that the amount of increase Y due to temperature rise is approximately equal to the amount of decrease X due to high speed rotation.

In other words, when the inner ring rotates at high speed,
The inner ring itself expands due to rotational centrifugal force, and the radial clearance of the bearing decreases. This is offset by the reduction in the fitting allowance, as the expansion of the hollow shaft due to the rise in temperature due to high-speed rotation becomes smaller than the expansion of the inner ring. There is.

As described above, when the bearing rotates at high speed and there is a rise in temperature, the radial clearance can be maintained at approximately the same value as the initial value, that is, in the case of a preload bearing, the amount of preload clearance remains the same as before rotation.

Based on the above discussion, the embodiment of the present invention will be further explained. As the rotation of the shaft increases, the inner ring raceway diameter expands by the amount shown in the diagram a. but,
In the preload bearing device of the present invention, the inner diameter of the inner ring is set in advance to be smaller than the outer diameter of the hollow shaft. In other words, the object is one that has a fitting margin (the fitting between the two is not a loose fit with a gap, but a tight fit so that the two do not shift in the axial and circumferential directions). Since the expansion of the outer diameter of the hollow shaft (diagram c) is smaller than that in diagram b), the fitting interference between the inner ring and the hollow shaft decreases as the rotation increases.
Therefore, the inner ring raceway diameter does not expand by an amount corresponding to the line d when the inner ring rotates independently. That is, the inner ring raceway diameter expands with rotation by an amount obtained by subtracting line d from line a. Therefore, when considering only the expansion due to the rotation of the inner ring and hollow shaft without considering changes due to temperature rise, which will be described later, the outer ring is stationary and does not expand, so the raceway diameter of the outer ring does not change.On the other hand, The raceway diameter of the inner ring increases by an amount commensurate with this amount of expansion, and the space between the two raceways becomes narrower.
The amount of preload clearance increases (the amount of negative clearance increases), and as a result, the preload on the bearing increases. For example, at a rotation speed of 20,000, the raceway diameter of the inner ring expands by 0.020mm, resulting in a
The negative clearance in the radial direction (0.074 mm in the axial direction at a contact angle of 15°) increases, and there is a risk that the preload will become excessive.

However, according to a preferred embodiment of the present invention, the coefficient of linear expansion of the hollow shaft is approximately 6×10 ^-6 , the inner ring,
The linear expansion coefficient of the outer ring and housing is approximately 12.5×
10 ^-6 , so at high speeds of around 20,000 revolutions, the temperature of the bearing device rises by about 30°C above the ambient temperature, and the amount of expansion of the hollow shaft is approximately 0.018 mm, and the amount of expansion of the inner diameter of the inner ring is approximately 0.038 mm. , there is a reduction in the fit interference of 0.020mm. In other words, the relative difference in the expansion of the outer ring raceway diameter and inner ring raceway diameter due to temperature rise is approximately 0.020 mm, which is the reduction in the fit margin mentioned above.
The amount of expansion of the inner ring raceway diameter corresponding to 85% is small, which acts to offset the 0.020mm expansion of the inner ring raceway diameter due to rotation, and the bearing preload clearance (minus clearance) increases. Therefore, excessive preload is prevented.

As explained above, the present invention makes the coefficient of linear expansion of the hollow shaft smaller than that of the inner ring, outer ring, and housing of the bearing, and takes advantage of the reduction in fitting interference caused by the temperature rise during high-speed rotation to improve rotation. This is a preload bearing device that can prevent an increase in preload due to the accompanying expansion of the inner ring.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the amount of expansion of each part and the amount of reduction in fitting interference as the rotation increases. Reference numeral 10 is a hollow shaft; is an inner circle.

Claims (1)

[Scope of Claims] 1. A hollow shaft and a housing that rotate at high speed, an inner ring that fits into the hollow shaft with necessary interference even during high speed rotation, an outer ring that fits into the housing, and the inner ring and the outer ring. The bearing comprises a large number of rolling elements disposed between the hollow shaft and the housing, and the bearing is incorporated in the hollow shaft and the housing so that they cannot move relative to each other in the axial direction, and in this state, the radial clearance of the bearing is negative. In a certain preload bearing device,
The linear expansion coefficients of the inner ring, the outer ring, and the housing are approximately the same, and the inner ring is rotated by rotational centrifugal force when the linear expansion coefficient of the hollow shaft is higher than the linear expansion coefficient of the inner ring, the outer ring, and the housing. A preload bearing device characterized in that the preload bearing device is set to be small enough to offset a decrease in the radial clearance of the bearing due to expansion, thereby preventing an increase in the amount of preload. 2. The linear expansion coefficient of the hollow shaft is approximately 6×10 ^-6 ,
The preload bearing device according to claim 1, wherein the inner ring, the outer ring, and the housing have linear expansion coefficients of approximately 12.5×10 ^-6 . 3. The preload bearing device according to claim 1, wherein the bearing is an angular ball bearing. 4. The radial clearance is made negative by arranging a spacer whose dimensions are adjusted between two angular ball bearings fitted on the hollow shaft.
The preload bearing device described in .