JP6012980B2 - Bearing device preload adjustment structure - Google Patents

Description

The present invention relates to a preload adjusting structure of the bearing device for use in a high speed in a machine tool spindle apparatus.

  Conventionally, the bearing preloading method used for machine tool spindle devices is a constant pressure preloading method in which only a certain load acts on the bearing with a spring or the like for the purpose of high-speed light cutting, and a fixed assembly position of the bearing is used. There is a fixed position preload system. Since this fixed position preloading method is intended for heavy cutting at low speed, it is often used with a preload applied. However, when a bearing loaded with a preload is operated at a high speed, the radial negative clearance increases mainly due to temperature rise of the inner ring and expansion due to centrifugal force. As a result, the preload becomes excessive, which may cause problems such as an increase in temperature and a decrease in bearing life.

  Considering machining accuracy and machining efficiency, we want to perform high-speed machining with the fixed position preload method, but the bearing rigidity and high-speed performance are contradictory factors, and it is difficult to achieve both. The following techniques have been proposed as methods for reducing the excessive preload generated when the bearing is operated at high speed (Patent Documents 1 to 3).

The method disclosed in Patent Document 1 uses a screw and a spring to provide a fixed position preload during heavy cutting at a mechanically low speed, and to apply a constant pressure preload by a spring at a high speed.
The method disclosed in Patent Document 2 is a method of providing a heat generating portion in an outer ring spacer disposed between bearings (back side) in an angular ball bearing combined with a back surface, and changing the size of the spacer by temperature control. It adjusts the bearing preload. In this method, at the time of heavy cutting at low speed, the preload is increased to increase the bearing rigidity. In this case, the spacer is heated to expand in the axial direction to increase the preload. On the other hand, at the time of light cutting at high speed, in order to suppress heat generation and improve the limit speed, the spacer is contracted by radiating heat contrary to that at low speed to reduce the preload.

  The method disclosed in Patent Document 3 adjusts the preload by changing the axial clearance of the bearing by moving a part of the outer ring of the combined bearing while positioning it stepwise in the axial direction. As an example, there is disclosed one that allows three-stage preload adjustment in the 0 to maximum rotational speed range. Specifically, the outer ring of the front two-row bearing of the four rows of angular ball bearings is fixed to the outer cylinder, and the bearing box on which the outer ring of the rear two-row bearing is fixed is axially used in three stages. The axial clearance of the bearing is changed by moving it in the axial direction.

JP-A-3-79205 JP 2006-64127 A JP-A-2-279203

The bearing preload during operation is affected by the temperature difference between the inner and outer rings. In general, when operating using steel inner and outer rings, the heat generated in the inner ring is less likely to dissipate compared to the outer ring side where the bearing housing is forcibly cooled.
Inner ring temperature> outer ring temperature. That is, the amount of expansion of the inner ring raceway diameter during operation becomes larger than the amount of expansion of the outer ring raceway diameter due to the centrifugal force due to the temperature rise and rotation. This is the main factor that increases the preload during operation.

Taking the factors of increasing the preload during operation into consideration, the following can be said when the characteristics of the technologies disclosed in the patent documents 1 to 3 are examined.
In the method disclosed in Patent Document 1, the structure becomes complicated and the cost becomes expensive.
In addition, the method disclosed in Patent Document 2 has a drawback that it takes time to increase the temperature of the spacer by the heating element or to cool it, and the responsiveness of the preload control is deteriorated. That is, it is suitable for long-time machining at a constant rotation speed, but is not suitable for a processing machine in which the rotation speed frequently changes.

  Further, as disclosed in Patent Document 3, the method of forcibly moving the bearing outer ring in the axial direction to adjust the preload is that the rear bearing portion has a double structure of the bearing housing and the outer cylinder, The number of parts increases, such as the need for parts to move and position the box in the axial direction. In addition, a hydraulic source is required as a means for moving the bearing housing for preload adjustment. Thus, this method has a problem that the cost for adjusting the preload is increased.

The object of the present invention is that preload adjustment can be performed with a relatively simple structure without requiring control of the temperature etc. from the outside, high support rigidity unique to the fixed position preload bearing is given at low speed, and simple control. the bearing position preload is to provide a preload adjusting structure of the bearing device can be achieved in the difficult high-speed rotation reaches, simple autonomous mechanism.

A preload adjusting structure for a bearing device according to the present invention includes a plurality of rolling bearing type bearings that support a common shaft with respect to a housing, and some or all of the plurality of bearings are angular ball bearings or conical bearings. In roller bearings in which each of these bearings is preloaded in a fixed position preload type, at least one bearing has a shaft so that the inner ring is always tightly fitted to the shaft within the maximum rotational speed of the bearing. the solid is constant, the rest of the bearing inner race becomes a tight fit in a rotation stop state, so as to be movable with respect to the axis become loose fit in a high-speed rotation of the above transition rotation speed of the less than maximum speed , the initial interference is set for the inner ring of the axis of each bearing. The “maximum rotational speed” is, for example, a rotational speed used in a machine tool or the like in which the bearing device is used, or an allowable maximum rotational speed of the bearing.

According to this configuration, since it is a fixed position preload type and at least one of the plurality of bearings is fixed to the shaft so that the inner ring is always tightly fitted to the shaft within the maximum rotational speed, Therefore, a high bearing rigidity is always obtained, and when used in a machine tool or the like, heavy cutting at a low speed can be accurately performed. The remaining bearings are interference-fitted in the rotation stop state or low-speed state, but the initial allowance for the inner ring shaft is sufficient so that it can move with respect to the shaft due to clearance fit at high-speed rotation above the transition rotational speed. Is set. Therefore, even if high-speed rotation is performed, it is avoided that the preload becomes excessive and excessive temperature rise and bearing life decrease are caused. In addition, since the preload adjustment is performed using the change in the tightening allowance depending on the rotation speed, no external control is required.
In this way, preload adjustment can be performed with a relatively simple structure without the need for external temperature control, etc., and at a low speed, high support rigidity peculiar to a fixed position preload bearing is provided, and a simple fixed position preload is provided. High-speed rotation that is difficult to achieve with this bearing can be achieved with a simple autonomous mechanism.

In the present invention, the transition rotational speed from the interference fit to the clearance fit may be arbitrarily set. For example, the transition rotational speed may be set to the upper limit of the speed range in which high support rigidity of the shaft is required. The “speed range where high support rigidity of the shaft is required” is a speed range where heavy cutting is performed, for example, when applied to the spindle of a machine tool.
Note that. The transition rotational speed is, for example, the following speed. There is a permissible value (in other words, permissible bearing temperature) of increased bearing preload due to an increase in rotational speed when the inner ring is an interference fit and fixed position preload. Interference fit on empirical, limit rotational speed at a constant position preload conditions, generally is 100 a man with d _m n values, to the speed and transition speed.

An annular variable width inner ring spacer is provided for positioning and fixing the inner ring of the bearing on the shaft, and this variable width inner ring spacer is composed of two annular inner ring spacer divided bodies having different radial expansion amounts during operation. The inner ring spacer divided body on the small expansion side has a tapered surface on the outer diameter side, and the inner ring spacer divided body on the large expansion side has a tapered surface on the inner diameter side. At the same time, axial positioning is performed.

In this case, among the plurality of bearings preloaded by the fixed position preload, the fitting of the bearing on the side in contact with the inner ring spacer split body with the shaft of the inner ring is an interference fit during low speed rotation less than the transition rotational speed. the so that clearance-fitted at the time of high-speed rotation of the above transition speed, the initial interference may be set.

Of the inner ring divided spacer segment of the two bodies, the inner ring divided spacer segment on the side in contact with the bearing, the radial expansion amount due to a temperature rise and the centrifugal force of a and during operation the tapered surface of the outer diameter side is small The other inner ring spacer divided body on the side in contact with the shoulder of the shaft has a tapered surface on the inner diameter side , and a material whose temperature increases during operation and the amount of radial expansion due to centrifugal force increases. It may be said.

The inner ring spacer divided body having the tapered surface on the outer diameter side may be made of ceramics, and the inner ring spacer divided body having the tapered surface on the inner diameter side may be made of steel.
The taper angle of the tapered surfaces of the two inner ring spacer divided bodies is determined in consideration of, for example, the difference in expansion between the inner ring spacer divided bodies, the preload adjustment amount, and the bite.

The operation of the preload adjustment in the case of using the variable width inner ring spacer composed of the two annular inner ring spacer divided bodies will be described. The number of bearings is two, and there is an inner ring spacer between them, and the inner ring spacer divided body having a convex tapered surface is made of ceramics, and the inner ring spacer divided body having a concave tapered surface is made of steel.
At low speed, the preload is set by the difference in the spacer width dimension between the outer rings of the two rows of bearings and the spacer width dimension between the inner rings. As the rotational speed increases, the interference between the inner ring and the shaft of the rear bearing is reduced due to the difference in centrifugal force acting on the inner ring and the shaft (inner ring> shaft). Makes it easier to move in the axial direction. Also, in the variable width inner ring spacer (two inner ring spacer divided bodies), the difference in centrifugal force between the ceramic inner ring spacer divided body and the steel inner ring spacer divided body due to the increase in rotational speed (between the ceramic inner ring spacers) Due to the difference in thermal expansion due to temperature (ceramic inner ring spacer split body <steel inner ring spacer split body) due to the temperature of the seat split body <steel inner ring spacer split body) The total width of the two inner ring spacer divisions decreases as the clearance increases. That is, the decrease in the inner ring positioning spacer width dimension accompanying the increase in the rotational speed moves the inner ring of the inner bearing in the axial direction, and acts in a direction that alleviates the increase in bearing preload. Conversely, when decelerating from a high speed, the inner ring of the back bearing is moved in the direction of increasing the preload due to the decrease in the centrifugal force and the temperature drop, and the initial preload state is restored.

  Here, of the two inner ring spacer divided bodies that become the variable width inner ring spacer, the ceramic inner ring spacer divided body is smaller in density and linear expansion coefficient than those made of steel and has a higher Young's modulus. It doesn't matter. Further, the taper portion angle of the two inner ring spacer divided bodies is set by the rotational speed used and the target preload adjustment amount during operation.

The above shows an example in which the inner ring position is automatically adjusted by the two inner ring spacer divided bodies each having a tapered surface. However , various springs may be used as a reference proposal example as follows .
For example, a spring for positioning and fixing the inner ring on the shaft may be provided adjacent to the inner ring of the bearing that becomes a clearance fit and can move with respect to the shaft at a high speed that is higher than the transition rotational speed.
In this case, a part of the spring may be an interference fit with respect to the shaft. The spring may be a disc spring.

In the present invention, when the inner ring spacer is formed as two annular inner ring spacer divided bodies, the inner ring spacer protrudes toward the inner ring of the bearing on the outer diameter portion of the inner ring spacer divided body on the side in contact with the bearing. There annular portion which mate to the outer diameter of the inner ring is set vignetting, the initial interference of the annular portion becomes a clearance fit in a rotation stop state, such that the interference fit is at a low speed of less than said transition speed it may be set.

  In this invention, you may set the interference with respect to the axis | shaft of the inner ring | wheel spacer division | segmentation body by the side which does not contact a bearing so that it may always become an interference fit.

Oite this inventions or references proposed example, the outer diameter of the spacer ring spacer divided body or springs of the two bodies is from said position adjacent to the inner ring of the bearing adjacent to opposite, the bearing An annular portion that protrudes toward the inner ring and has an inner diameter that fits the outer diameter of the inner ring is provided, and the initial tightening allowance of the annular portion is a clearance fit when the rotation is stopped, and the inner ring and the shaft are a clearance fit. It may be set so as to be an interference fit at a high rotation speed higher than the transition rotation speed.

  In this case, the annular portion may be a separate component from the spacer function portion on the inner periphery of the spacer. Further, in this case, the tightening allowance for the spacer shaft may be set so as to always be an interference fit.

A machine tool according to the present invention includes a bearing spindle having a preload adjusting structure for a bearing device having any one of the configurations of the present invention.
According to this configuration, the rigidity of the bearing spindle at low speed can be increased and high-speed rotation can be performed, so that heavy cutting is possible and machining accuracy can be improved.

In the machine tool having this configuration, the transition rotational speed at which the bearing device transitions from the interference fit to the clearance fit may be set to be equal to or higher than the maximum rotational speed in heavy cutting required for the machine tool.
According to this configuration, heavy cutting at low speed can be performed with high accuracy, light cutting at high speed can be performed, and processing efficiency can be improved.

Preload adjusting method of bearings apparatus this is provided with a bearing of a plurality of rolling bearings shaped supporting a common shaft relative to the housing, conical part or all of the bearings of these plurality of bearings or angular contact ball bearings In the preload adjustment method of the bearing device in which each of these bearings is preloaded in a fixed position preload type, at least one of the bearings is such that the inner ring is always fixed to the shaft within the maximum rotation speed of this bearing, and the remaining The bearing is characterized in that the preload adjustment is performed by moving the inner ring in the axial direction during operation.
According to this method, preload adjustment can be performed with a relatively simple structure without requiring control of the temperature and the like from the outside. Moreover, high support rigidity peculiar to the fixed position preload bearing can be given at a low speed, and high speed rotation difficult to achieve with a simple position preload bearing can be achieved with a simple autonomous mechanism.

A preload adjusting structure for a bearing device according to the present invention includes a plurality of rolling bearing type bearings that support a common shaft with respect to a housing, and some or all of the plurality of bearings are angular ball bearings or conical bearings. In roller bearings in which each of these bearings is preloaded in a fixed position preload type, at least one bearing has a shaft so that the inner ring is always tightly fitted to the shaft within the maximum rotational speed of the bearing. The remaining bearings can be moved with respect to the shaft with an interference fit when the inner ring is in a rotation-stopped state and a clearance fit at a high rotation speed higher than a predetermined transition rotational speed less than the maximum rotational speed. As described above, an initial tightening allowance for the inner ring shaft of each bearing is set, and an annular variable width inner ring spacer is provided for positioning and fixing the inner ring of the bearing to the shaft. Is composed of the inner ring divided spacer segment of the annular direction expansion amounts are different two bodies, the inner ring divided spacer segment side of expansion of small has a tapered surface on the outer diameter side, the inner ring spacer side of the expansion of large The divided body has a tapered surface on the inner diameter side, and the axial positioning of the inner ring is performed by fitting these tapered surfaces. For this reason, preload adjustment can be performed with a relatively simple structure without requiring control of temperature and the like from the outside. Moreover, high support rigidity peculiar to the fixed position preload bearing can be given at a low speed, and high speed rotation difficult to achieve with a simple position preload bearing can be achieved with a simple autonomous mechanism.

  Since the machine tool of the present invention includes the bearing spindle having the preload adjusting structure for the bearing device having any one of the structures of the present invention, the bearing spindle can be increased in rigidity at a low speed and can be rotated at a high speed, thereby improving machining accuracy. Can be improved.

It is sectional drawing of the machine tool spindle apparatus using the preload adjustment structure of the bearing apparatus concerning one Embodiment of this invention. It is an expanded sectional view of the part of the preload adjustment structure. It is the preload curve showing the preload adjustment by the preload adjustment structure. It is explanatory drawing which shows the mechanism of the preload adjustment in the same preload adjustment structure. It is sectional drawing of the preload adjustment structure of the bearing apparatus concerning a reference proposal example . It is the preload curve showing the preload adjustment by the preload adjustment structure. It is sectional drawing of the preload adjustment structure of the bearing apparatus concerning other embodiment of this invention. It is sectional drawing of the preload adjustment structure of the bearing apparatus concerning further another embodiment of this invention. It is sectional drawing of the preload adjustment structure of the bearing apparatus concerning further another embodiment of this invention.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a cross-sectional view of an example of a machine tool spindle device to which a preload adjusting structure for a bearing device of this embodiment is applied. In this machine tool spindle apparatus, a tool (not shown) is attached to the front side (left side of the figure) of the spindle 1, and a drive source such as a motor is connected to a rotation transmission mechanism (not shown) on the rear side (right side of the figure). ). A plurality of rolling bearing type bearings 3, 4, 5 that support the main shaft 1 with respect to the housing 2 as a common shaft are provided. Two angular ball bearings 3 and 4 that receive a radial load and an axial load are arranged in the rear side on the front side, which is the tool mounting side in the machine tool spindle device, and the main shaft 1 is steady while receiving the radial load on the rear side. A cylindrical roller bearing 5 for the purpose is arranged. These bearings 3 to 5 are respectively fitted and fixed to the main shaft 1.

  The inner rings 3a and 4a of the two angular ball bearings 3 and 4 include an inner ring spacer 6, a variable width inner ring spacer 10, an inner ring spacer 7 for setting an initial preload, a bearing fixing nut 13, and a shoulder portion of the main shaft 1. The position in the axial direction is restricted by the end face 1aa of 1a. The variable width inner ring spacer 10 includes two inner ring spacer divided bodies 11 and 12. The positions of the outer rings 3 b and 4 b are restricted by the lid member 14 fixed to the front end portion of the housing 2, one outer ring spacer 8, and the stepped portion 2 a of the housing 2. The inner ring 5a of the cylindrical roller bearing 5 on the rear side is regulated in the axial direction by a bearing fixing nut 15 and a bearing retainer 16 which are screwed to the main shaft 1, and an end surface 1ab of the shoulder 1a of the main shaft 1, and the outer ring 5b is The axial position is regulated by the lid member 17 fixed to the rear end portion of the housing 2 and the stepped portion 2b of the housing 2.

  In general, the angular contact ball bearings 3 and 4 on the front side and the cylindrical roller bearing 5 on the rear side generally have a 0 to negative clearance in the bearing after assembly in order to ensure the rigidity of the main shaft 1. For the lubrication of the bearings, methods such as grease, jet lubrication, and air oil lubrication are used. FIG. 2 is an enlarged cross-sectional view of a portion of the machine tool spindle device in which the preload adjusting structure of the bearing device of this embodiment is provided. FIG. 2 shows a structure in which the inner ring spacer 6 is omitted and the bearing fixing nut 13 is brought into direct contact with the front end face of the inner ring 3 a of the angular ball bearing 3.

  The preload adjusting structure of the bearing device of this embodiment performs preload adjustment during operation of the two angular ball bearings 3 and 4. Normally, when the angular ball bearing is operated, the bearing preload increases due to the bearing temperature rise (inner ring temperature rise> outer ring temperature rise) and centrifugal force accompanying rotation as described above. In the preload adjusting structure of the bearing device of this embodiment, the bearing preload during operation is moved by moving the inner ring 4a of the angular ball bearing 4 on the rear side of the two angular ball bearings 3 and 4 in the axial direction. Adjust the preload by changing the internal clearance.

  The features of the preload adjusting structure of the bearing device of this embodiment are the following two points. The first point is the fitting of the inner rings 3a, 4a of the angular ball bearings 3, 4. That is, of the two angular ball bearings 3, 4, the inner ring 3 a of the front angular ball bearing 3 is an interference fit that secures a tightening margin when the maximum rotational speed is reached, and the inner ring 4 a of the inner angular ball bearing 4. The initial tightening allowance is such that the fitting with the main shaft 1 becomes a clearance fit in a high speed range where preload adjustment is required.

The second feature is that the inner ring spacer 10 interposed between the inner ring 4a of the angular ball bearing 4 on the back side and the shoulder 1a of the main shaft 1 has a width formed by two inner ring spacer divided bodies 11 and 12. It is configured as a variable inner ring spacer. Of two bodies of the inner ring divided spacer segment 11 and 12, the inner ring divided spacer segment 11 disposed on the inner ring 4a side angular ball bearing 4, the density of such ceramics are manufactured by a small material of small linear expansion coefficient, the spindle The other inner ring spacer divided body 12 arranged on the side of the shoulder 1a is made of steel. The one inner ring spacer divided body 11 located on the inner ring 4a side is provided with a convex tapered surface 11a having an angle α with a large diameter on the inner ring 4a side, and another body located on the shoulder 1a side of the main shaft 1. The inner ring spacer divided body 12 is formed with a concave tapered surface 12a having an angle α with a large diameter on the inner ring 4a side, and both the inner ring spacer divided bodies 11 and 12 are tapered surfaces 11a and 12a. It is in a fitted state.

  The angle α of the tapered surfaces 11a and 12a is determined in consideration of the axial movement amount of the inner inner ring 4a for mitigating the increase in bearing preload that occurs during operation, and the reproducibility of the movement, but is small. It is set not to become an angle. And the initial fitting with the main shaft 1 of the inner ring spacer divided body 11 located on the inner ring 4a side is set to a size that does not cause an interference fit in the operating rotational speed range. In addition, the initial fitting of the inner ring spacer divided body 12 positioned on the shoulder 1a side of the main shaft 1 with the other inner ring spacer divided body 11 is adjusted when the inner ring spacer divided bodies 11 and 12 are assembled. It is desirable to have a slight interference fit considering the core.

Bearing preload adjustment during operation performed by the preload adjusting structure of the bearing device configured as described above is as follows.
From the start of operation of the angular ball bearings 3 and 4 to a certain speed, both the bearings 3 and 4 have an interference fit, and the bearing rigidity is ensured to cope with heavy cutting. In a higher speed range (ie, higher than the transition rotational speed), the inner ring 3a of the angular contact ball bearing 3 on the front side remains in an interference fit, and the inner ring 4a of the angular contact ball bearing 4 on the back side shifts from an interference fit to a clearance fit. To do. At this time, in the two inner ring spacer divided bodies 11 and 12 for positioning the angular ball bearings 3 and 4, the radial direction between the inner ring spacer divided bodies 11 and 12 due to differences in linear expansion coefficient, density, and Young's modulus. The difference in expansion amount occurs. Since the inner ring spacer divided body 11 having the convex tapered surface 11a, that is, the tapered surface 11a on the outer diameter side is made of ceramics or the like, it is made of steel having the concave tapered surface 12a, that is, the tapered surface 12a on the inner diameter side. The amount of radial expansion during operation is smaller than that of the inner ring spacer divided body 12, and the taper fits in a direction in which a clearance is generated. That is, the inner ring spacer divided body 11 positioned on the inner ring 4a side is moved in the axial direction corresponding to the clearance of the tapered fitting portion. As a result, the inner ring 4a of the angular contact ball bearing 4 on the back side can be easily moved in the axial direction by the bearing preload, and the bearing preload can be adjusted.

  In addition, it is disadvantageous in terms of bearing rigidity that the inner ring 4a of the angular contact ball bearing 4 on the back side becomes a clearance fit in the radial direction at a high speed region, but the axial preload maintains a working state, There is no practical problem even in the high-speed range where light cutting is mainly used. Further, when decelerating from a high speed, the steel inner ring spacer divided body 12 having the tapered surface 12a on the inner diameter side is contracted in the radial direction, conversely to the speed increase, so that the angular ball bearing on the back side 4 inner ring 4a moves to the side where preload increases.

  FIG. 3 and FIG. 4 conceptually show this preload adjustment method. As shown in FIG. 3, in this preload adjusting method, two preload curves can be set. One corresponds to the curve I corresponding to heavy cutting, and is a preload diagram in a region (solid line portion) in which the space between the inner ring 4a of the inner angular ball bearing 4 and the main shaft 1 is an interference fit. The second curve II is a diagram corresponding to high-speed light cutting. The inner ring 4a of the inner angular ball bearing 4 and the main shaft 1 have a clearance fit, and the two inner ring spacer divided bodies 11, 12 are provided. FIG. 6 is a preload diagram with axial movement of the inner ring 4a of the inner angular ball bearing 4 on the inner side generated by a difference in expansion due to the centrifugal force and temperature rise (inner ring spacer divided body 12> inner ring spacer divided body 11).

  For example, it is assumed that the operation is started from the point A where the initial preload is loaded. At the start of operation, the bearing preload increases due to the temperature rise and centrifugal force of the inner rings 3a and 4a of the angular ball bearings 3 and 4. At the point B, the inner ring 4a of the angular contact ball bearing 4 on the back side shifts from an interference fit to a clearance fit. On the side higher than the point B, the bearing preload increases due to the increase in rotational speed, and the two inner ring spacer split bodies 11, 12 The preload diagram II is set according to the balance of the preload mitigating action. Therefore, the rotational speeds at points B and C are the initial engagement (point B) with the main shaft 1 of the inner ring 4a of the angular contact ball bearing 4 on the back side and the maximum rotational speed (point C) that is the upper limit of the bearing preload. Is set. That is, the bearing rigidity is high in the speed range from point A to point B, and can cope with heavy cutting. The bearing rigidity in the speed range from point B to point C is slightly inferior to that at low speed, but can sufficiently cope with light cutting.

FIG. 4 shows the effect of reducing the bearing preload by the two inner ring spacer split bodies 11 and 12, the difference in expansion between the inner ring spacer split bodies 11 and 12, the spacer taper surface angle α and the axial direction of the inner ring 4a. It shows the relationship of the amount of movement. The inner ring spacers 11 and 12 in operation, which take into account the initial fitting of the inner ring 4a of the inner angular ball bearing 4 on the back side, expansion due to temperature rise and centrifugal force, and the amount of expansion during operation are small. The radial expansion amount of the inner ring spacer divided body 11 positioned on the inner ring 4a side is Yc, the radial expansion amount of the inner ring spacer divided body 12 positioned on the shoulder 1a side of the main shaft 1 is Ys, and the taper surface angle is α. , Where Xc is the amount of axial movement of the inner ring 4a due to the difference in expansion between the two inner ring spacer split bodies 11, 12,
Tan α = (Ys−Yc) / Xc
Xc = (Ys-Yc) / Tanα
The relationship is obtained. That is, the amount of radial expansion (Ys, Yc) during operation of the two inner ring spacer divided bodies 11, 12 is obtained by calculation, and the necessary taper surface angle α is obtained from the necessary inner ring movement amount (Xc). Can do.

From the above, the procedure for designing this preload adjustment method is as follows.
(1) Determination of initial preload load and initial tightening allowance of the inner ring 4a of the main shaft 1 and the angular ball shaft 4 on the back side:
The initial preload (point A) and the initial tightening allowance of the inner ring 4a of the rear angular ball bearing 4 are determined from the bearing rigidity and rotational speed (point B) required for heavy cutting.
(2) Setting of the axial movement amount (Xc) of the inner ring 4a of the back angular ball bearing 4:
In the rotational speed at point B and the bearing temperature distribution in that state, the initial bearing internal clearance at which the bearing preload becomes zero is obtained by calculation, and the axial position of the inner ring 4a in that case is Xa. From the target maximum rotational speed and the expected upper limit (point C) of the bearing preload, the bearing internal clearance in that state is obtained, and the axial position of the inner ring 4a in that case is Xb.
Xc = (Xb-Xa)
Can be obtained as

(3) Obtain the taper angle α of the two inner ring spacer divided bodies 11 and 12:
The expansion amount difference (Ys−Yc) between the two inner ring spacer divided bodies 11, 12 from the B point rotation speed to the C point rotation speed is calculated. The taper angle α is obtained from the expansion amount difference (Ys−Yc) and the axial movement amount (Xc) of the inner ring 4a.
The point to be noted here is that when calculating the initial bearing internal clearance or the like by calculation, it is necessary to consider the bearing temperature, centrifugal force, and fitting of the inner ring 4a. In addition, the bearing temperature expected at the maximum rotational speed must be obtained in advance through experiments.

  Thus, the preload adjustment by the preload adjusting structure of the bearing device of this embodiment is performed using the centrifugal force accompanying the rotational speed of the two inner ring spacer split bodies 11 and 12 and the difference in linear expansion coefficient. The bearing preload is adjusted by moving the inner ring 4a of the angular ball bearing 4 in the axial direction. In this embodiment, the preload adjustment of the angular ball bearings 3 and 4 has been described. However, this preload adjustment method can be applied to a tapered roller bearing having a contact angle as another example.

According to the preload adjusting structure of this bearing device, the effects listed below can be obtained.
(1) Special equipment and structure for adjusting the preload are not required on the outer ring or the housing side, and the bearing preload can be adjusted with a simple configuration.
(2) Increase in bearing preload during operation is mitigated, and further speeding-up, that is, improvement in machining efficiency, or extension of bearing life can be achieved.
(3) The initial preload can be increased, the spindle rigidity at low speed can be increased, and improvement in machining accuracy can be expected.
(4) The amount of heat generated by the bearing under high-speed rotation can be reduced, and as a result, the thermal displacement of the main shaft can also be reduced.

  When the bearing device preload adjustment structure described above is applied to the bearing spindle, the preload adjustment of the bearing device can be performed with a relatively simple structure without the need for external temperature control, etc. And high speed rotation is possible.

In addition, the machine tool equipped with the bearing spindle can increase the rigidity of the bearing spindle at a low speed and can be rotated at a high speed, so that the machining accuracy can be improved.
Further, in the spindle device in the machine tool, the rotational speed at which the fitting state of the bearing in the bearing device with the shaft of the inner ring where the bearing can move is changed from interference fit to clearance fit in heavy cutting required for the machine tool. Since it is set to be higher than the maximum rotation speed, heavy cutting at low speed and light cutting at high speed are possible, and the processing efficiency can be improved.

  Further, in the preload adjusting method of the bearing device, the inner ring 3a of the front angular ball bearing 3 is always fixed to the main shaft 1 within the maximum rotational speed of the angular ball bearing 3, and the inner angular ball bearing 4 is Since the preload adjustment is performed by moving the inner ring 4a in the axial direction during operation, the preload adjustment can be performed with a relatively simple structure without requiring control of the temperature or the like from the outside. Moreover, high support rigidity peculiar to the fixed position preload bearing can be given at a low speed, and high speed rotation difficult to achieve with a simple position preload bearing can be achieved with a simple autonomous mechanism.

5 and 6 show a reference proposal example . In this preload adjusting structure of the bearing device, a spring 20 acting in the axial direction as shown in FIG. 5 is used instead of the two inner ring spacer divided bodies 11 and 12 used in the previous embodiment. Other configurations are the same as those in the previous embodiment. In this case, if the spring 20 is biased with respect to the main shaft 1, vibration due to unbalance increases, so it is desirable that a part of the spring 20 be an interference fit with respect to the main shaft 1. Therefore, for example, a disc spring may be used as the spring 20.

A preload diagram in the case of this reference proposal example using the spring 20 is shown in FIG. With reference to this preload diagram, the design procedure when the spring 20 is used will be described below.
(1) Point C ′ is the maximum rotational speed required for light cutting. The preload is selected so as to be a preload that can reach this rotational speed obtained in advance through experiments. A spring 20 capable of applying this preload is selected.
(2) Point B ′ is the upper limit rotational speed at which heavy cutting is required, or a slightly higher rotational speed. Further, at the point B ′, the tightening allowance between the inner ring 4a and the main shaft 1 is set to be zero. The reason why the rotational speed is slightly higher is to consider the influence of the frictional force at the fitting portion between the main shaft 1 and the inner ring 4a.

(3) Between the points B'-C ', the inner ring 4a and the main shaft 1 are clearance fits, and the load from the spring 20 corresponds to the preload load of the bearing, so that the value is substantially constant. Therefore, since the load inside the bearing does not increase even if the rotational speed is increased, the limit rotational speed can be easily increased.
(4) Between the points A ′ and B ′, the inner ring 4 a is fitted to the main shaft 1 with an interference fit and does not move in the axial direction. Therefore, a fixed position preload state is established. As a result, the preload load inside the bearing becomes an upward curve as shown in FIG. 6 due to the expansion of the inner ring 4a due to heat and centrifugal force. However, since the inner ring 4a and the main shaft 1 are fixed with an interference fit, the support rigidity of the main shaft 1 by the bearing is high, and heavy cutting can be performed.

In the real施形status and references proposed example described above, one also the inner ring 4a is a clearance fit with respect to the main shaft 1 under high speed rotation, it allows the bias of the radial direction of the spindle 1 relative to the inner ring 4a is generated There is sex. When this is applied to a machine tool, it is directly related to machining accuracy, which is a problem. In order to solve this, it is only necessary to provide a component that supports the inner ring 4a on the outer diameter side when the inner ring 4a expands under high-speed rotation and prevents radial deviation from the main shaft 1. Embodiments in which such measures are taken are shown in FIGS.

  In the embodiment shown in FIG. 7, in the embodiment shown in FIGS. 1 to 4, a part of the outer diameter portion of the inner ring spacer divided body 11 adjacent to the inner ring 4 a is disposed outside the outer diameter part of the inner ring 4 a. A protruding annular portion 11b is provided. The inner diameter of the annular portion 11b is a clearance fit with the outer diameter of the inner ring 4a when the main shaft 1 is stationary. If the material of the inner ring spacer divided body 11 is selected so that the expansion due to the centrifugal force of the inner ring spacer divided body 11 having the tapered surface 11a on the outer diameter side is smaller than the expansion of the inner ring 4a, under high speed rotation, The inner ring 4a expands and becomes an interference fit with the protruding annular part 11b of the inner ring spacer divided body 11, and the play (backlash) in the radial direction of this part is eliminated. Further, the inner ring spacer divided body 12 having the tapered surface 12a on the inner diameter side is guided in the radial direction by the tapered surfaces 11a and 12a with respect to the inner ring spacer divided body 11 having the tapered surface 11a on the outer diameter side. Therefore, if the inner ring spacer divided body 11 having the tapered surface 11a on the outer diameter side and the main shaft 1 are tightly fitted, play in the radial direction between the inner ring 4a and the main shaft 1 can be eliminated.

  In the embodiment shown in FIG. 8, in the embodiment shown in FIGS. 1 to 4, an annular portion 7 a that protrudes in the axial direction from the outer diameter portion of the inner ring spacer 7 between the angular ball bearings 3 and 4 is provided. The inner diameter of the annular portion 7a is configured to be an interference fit only under the outer diameter of the inner ring 4a and under high speed rotation. Under high-speed rotation, it is necessary to make an interference with the inner ring 4a so that the inner ring 4a does not hinder the axial movement of the inner ring 4a. When the main shaft 1 is stationary, the annular portion 7a protruding in the axial direction from the outer diameter portion of the inner ring spacer 7 and the inner ring 4a need to be fitted with a clearance. Further, as the material of the inner ring spacer 7, it is necessary to select a material that is less expanded by centrifugal force than the inner ring 4a. Further, the main shaft 1 and the inner ring spacer 7 need to have an interference fit in a rotational speed region where the inner ring 4a is a clearance fit with the main shaft 1. In the same speed range, the ring portion 7a of the inner ring spacer 7 and the inner ring 4a need to have a slight interference fit. At that time, the lower the frictional force, the more freely the inner ring 4a can move. Therefore, it is preferable to install the angular ball bearing 4 having a small surface treatment such as a solid lubricant and a smaller outer diameter shoulder of the inner ring.

  The embodiment shown in FIG. 9 has a structure similar to that of the embodiment shown in FIG. 8, but the inner ring spacer 7 with an annular portion in the embodiment of FIG. 8 has a structure divided into two bodies. Other configurations are the same as those in the embodiment of FIG. In the inner ring spacer 7, only the ring part 7 a which is a separate member contacts the inner ring 4 a under high speed rotation in the radial direction. In this case, only the separate annular portion 7a is desired to suppress expansion against centrifugal force, and only this part may be manufactured by selecting a light and high rigidity material such as ceramics. Further, the spacer main body 7A and the annular portion 7a of the inner ring spacer 7 are both simple annular shapes, and it is easy to improve the processing accuracy. In this case, the inner ring spacer 7 with an annular portion selects a tightening allowance that is always an interference fit with the main shaft 1.

DESCRIPTION OF SYMBOLS 1 ... Main shaft 1a ... Shoulder part 2 ... Housing 3 ... Front side angular contact ball bearing 3a ... Inner ring 3b ... Outer ring 4 ... Back side angular contact ball bearing 4a ... Inner ring 4b ... Outer ring 7 ... Inner ring spacer 7a ... Ring part 7A ... Spacer body DESCRIPTION OF SYMBOLS 10 ... Variable-width inner ring | wheel spacer 11, 12 ... Inner ring spacer division body 11a, 12a ... Tapered surface 11b ... Ring part 20 ... Spring

Claims (6)

A plurality of rolling bearing type bearings that support a common shaft with respect to the housing are provided, and some or all of the plurality of bearings are angular ball bearings or tapered roller bearings. In the bearing device preloaded in the preload type,
At least one bearing is fixed to the shaft such that the inner ring is always in an interference fit with the shaft within the maximum rotational speed of the bearing, and the remaining bearings are in an interference fit when the rotation is stopped, The initial tightening allowance for the shaft of the inner ring of each bearing is set so that it can move with respect to the shaft by high-speed rotation that is higher than the transition rotational speed less than the maximum rotational speed, and the inner ring of the bearing is An annular variable width inner ring spacer that is positioned and fixed to the inner ring spacer is provided. The variable width inner ring spacer is composed of two annular inner ring spacer divided bodies having different radial expansion amounts during operation, and has a small expansion amount. The inner ring spacer divided body on the side has a tapered surface on the outer diameter side, and the inner ring spacer divided body on the large expansion side has a tapered surface on the inner diameter side, and the shaft of the inner ring is fitted by fitting these tapered surfaces. Bearing preload, characterized in that the positioning is carried out in a direction Integer structure. And have you the preload adjusting structure of the bearing device according to claim 1, among a plurality of bearings that are preloaded in position preloading, fitting between the inner race of the axial side of the bearing in contact with the inner ring divided spacer segment is A preload adjustment structure for a bearing device in which an initial tightening allowance is set so that an interference fit is achieved at a low speed rotation less than the transition rotational speed and a clearance fit is achieved at a high speed rotation greater than the transition rotational speed. And have you the preload adjusting structure of the bearing device according to claim 1 or claim 2, of the inner ring divided spacer segment of the two bodies, the inner ring divided spacer segment on the side in contact with the bearing, taper of the outer diameter side The inner ring spacer divided body on the side in contact with the shaft shoulder portion has a tapered surface on the inner diameter side. A preload adjustment structure for a bearing device that is made of a material that has a temperature increase during operation and a radial expansion amount due to centrifugal force. And have you the preload adjusting structure of the bearing device according to any one of claims 1 to 3, the inner ring divided spacer segment having a tapered surface of the outer diameter side is made of ceramics, the taper of the inner diameter side The inner ring spacer divided body having a surface is a preload adjusting structure of a bearing device made of steel. And have you the preload adjusting structure of the bearing device according to any one of claims 1 to 4, the outer diameter of the inner ring divided spacer segment of the side in contact with the bearing, and projects toward the inner ring of the bearing An annular part whose inner diameter fits with the outer diameter of the inner ring is provided, and the initial tightening allowance of the annular part is a clearance fit when the rotation is stopped, and an interference fit when the rotational speed is lower than the transition rotational speed. Preload adjustment structure for the set bearing device.   A machine tool comprising a bearing spindle having the preload adjusting structure for a bearing device according to any one of claims 1 to 5.

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