Oblique contact double row ball bearing and method of imparting preload in the ball bearing

To provide a oblique contact double ball bearing and a pre-load adding method for the ball bearing capable of easily adding the pre-load by performing adjustment for adding the pre-load in a wide adjustment range. In this oblique contact double ball bearing, clearances between balls and raceways and on one row are made different from clearances between balls and raceways on the other row so as to apply a thrust load to inner and outer rings, and add the pre-load to the inner and outer rings.

FIELD OF THE INVENTION

The present invention relates to an oblique contact double row ball bearing for supporting a pinion shaft of a differential device additionally provided in a vehicle or the like under a free rotation, more specifically to an oblique contact double row ball bearing in which pitch circle diameters of double rows are different to each other, in other words, raceway diameters of the double rows are different to each other, and a method of imparting a preload to the ball bearing.

BACKGROUND OF THE INVENTION

A tapered roller bearing is used as a roller bearing for supporting a pinion shaft of a differential device additionally provided in a vehicle, or the like under a free rotation. The tapered roller bearing has a large load capacity, however, its rotation torque is large. Therefore, an oblique contact ball bearing (angular contact ball bearing) may be incorporated into the differential device or the like in place of the tapered roller bearing (for example, see the Patent Document 1), or an oblique contact double row ball bearing called a tandem double row ball bearing in which pitch circle diameters of double rows are different to each other, in other words, raceway diameters of the double rows are different to each other, may occasionally be incorporated into the differential device or the like.

The oblique contact double row ball bearing having the pitch circle diameters different to each other is effectively used particularly for the opinion shaft of the differential device or the like because the rotation torque thereof is smaller than that of the tapered roller bearing and the load capacity is sufficiently large.

In the case of incorporating these bearings into the differential device, the bearings are managed and stored in a state where a preload as prescribed is applied thereto.Patent Document 1: No. 2003-156128 of the Japanese Patent Application Laid-Open

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

The preload is controlled (adjusted) in the bearing through the measurement of the rotation torque of the bearing. Therefore, a range where the preload is set is increased as the rotation torque is larger, which facilitates the adjustment. As described earlier, the tapered roller bearing is advantageous in its large load capacity and at the same time the rotation torque thereof is large. As a result, the adjustment range of the preload to be set with respect to the bearing is large, which makes it easy to control the preload. However, in the oblique contact ball bearing, which has the structure of the ball bearing, the rotation torque is small and the adjustment range of the preload to be set with respect to the bearing is thereby reduced. As a result, it is difficult for the preload to be set with a high accuracy.

A main object of the present invention is to facilitate the control of the preload in the oblique contact ball bearing.

Means for Solving the Problem

In order to achieve the foregoing object, an oblique contact double row ball bearing according to the present invention comprises double rows of balls axially interposed in raceways of inner and outer rings, wherein an inner clearance between the balls in one of the rows and the raceway in which the balls are rolled, and an inner clearance between the balls in the other row and the raceway in which the balls are rolled are different to each other.

In a method of imparting a preload to the oblique contact double row ball bearing according to the present invention, the inner clearance between the balls in one of the rows and the raceway of the inner and outer rings corresponding to the one of the rows in which the balls are rolled, and the inner clearance between the balls in the other row and the raceway of the inner and outer rings corresponding to the other row in which the balls are rolled, are set to be different to each other, and then a load is given to the inner and outer rings so that the inner clearances are sequentially reduced in order to provide the preload to the inner and outer rings.

In the oblique contact double row ball bearing according to the present invention, any one of the clearances may be reduced earlier than the other.

The preload to be imparted to the bearing is generally obtained through measurement of a rotation torque. The case of imparting the preload to the oblique contact double row ball bearing is considered here. In this case, when a thrust load S to be imparted to the inner and outer rings is hypothetically a “S2” value, comparison of an adjustment range “T1” of a rotation torque T in a conventional oblique contact double row ball bearing to an adjustment range “T2” of the rotation torque T in the oblique contact double row ball bearing according to the present invention, which correspond to the “S2” value, it becomes T2>T1. Therefore, when it is tried to obtain the same preload, the preload can be adjusted in the range wider in the oblique contact ball bearing according to the present invention than that of the conventional oblique contact ball bearing, which consequently makes it easy to impart the preload with a high accuracy.

In addition, the preload may be set while the thrust load “S2” is being adjusted in the range of [S1]-[S3] in view of its tolerance in setting the preload. Such a case is considered. Comparing an adjustment range [T3] of the rotation torque T in the conventional bearing to an adjustment range [T4] of the rotation torque T in the bearing according to the present invention, T4>T3is obtained. When it is tried to obtain the same preload, the adjustment range of the rotation torque T (in other words, adjustment range of the preload) is increased in the bearing according to the present invention in comparison to that of the conventional bearing. As a result, the preload can be easily and accurately imparted.

Effect of the Invention

According to the present invention, the preload can be adjusted in the adjustment range wider than that of the conventional oblique contact bearing by making the rotation torque large, and the preload can be thereby accurately and easily imparted.

DESCRIPTION OF REFERENCE SYMBOLS

PREFERRED EMBODIMENT OF THE PRESENT INVENTION

A preferred embodiment of the present invention is described referring to the drawings.FIG. 1is a sectional view illustrating a schematic constitution of a differential device.FIG. 2is a sectional view in which double row ball bearings are enlarged.

As shown inFIG. 1, a differential device1comprises a differential case2. The differential case2comprises a front case3and a rear case4. These cases3and4are coupled to each other by a bolt/nut2aso as to thereby be integrated. Annular walls27A and27B in which ball bearings are applied are formed in the front case3.

The differential case2comprises internally a differential speed-change mechanism5for differentially gearing right and left wheels, and a pinion shaft (drive pinion)7having a pinion gear6on one side thereof. The pinion gear6is meshed with a ring gear8of the differential speed-change mechanism5. A shaft part9of the pinion shaft7is formed in a stepwise shape so that a diameter thereof is gradually reduced on the other side than one side thereof.

The one side of the shaft part9of the pinion shaft7is supported by the annular wall27A of the front case3so as to freely rotate around an axial center via a first double row ball bearing10. The other side of the shaft part9of the pinion shaft7is supported by the annular wall27B of the front case3so as to freely rotate around the axial center via a second double row ball bearing25.

As shown inFIG. 2, the first double row ball bearing10is an oblique contact double row ball bearing, and comprises a single first outer ring11fitted to an inner peripheral surface of the annular wall27A and a first assembly component21. The first assembly component21is assembled into the first outer ring11from the pinion-gear side toward the opposite side of the pinion gear6(hereinafter, referred to as counter-pinion-gear side) along an axial direction so as to thereby constitute the first double row ball bearing10.

The first outer ring11has a structure of a counterbored outer ring. More specifically, the first outer ring11comprises a large diameter outer ring raceway11aon the pinion-gear side and a small diameter outer ring raceway11bon the counter-pinion-gear side. A planar part11cis formed between the large diameter outer ring raceway11aand the small diameter outer ring raceway11b. The planar part11chas a diameter larger than that of the small diameter outer ring raceway11band continuous to the large diameter outer ring raceway11a. An inner peripheral surface of the first outer ring11is thus formed in the stepwise shape.

The first assembly component21comprises a single first inner ring13, a large-diameter-side row of balls15, a small-diameter-side row of balls16, and retainers19and20. The first inner ring13has a structure of a counterbored inner ring. More specifically, the first inner ring13comprises a large diameter inner ring raceway13aand a small diameter inner ring raceway13b. The large diameter inner ring raceway13afaces the large diameter outer ring raceway11ain a radial direction. The small diameter inner ring raceway13bfaces the small diameter outer ring raceway11bin a radial direction. A planar part13cis formed between the large diameter inner ring raceway13aand the small diameter inner ring raceway13b. The planar part13chas a diameter larger than that of the small diameter inner ring raceway13band continuous to the large diameter inner ring raceway13a. An outer peripheral surface of the first inner ring13is thus formed in the stepwise shape.

The large-diameter-side row of balls15are fitted to place on the pinion-gear side, in other words, between the large diameter outer ring raceway11aand the large diameter inner ring raceway13a. The small-diameter-side row of balls16are fitted to place on the counter-pinion-gear side, in other words, between the small diameter outer ring raceway11band the small diameter inner ring raceway13b.

In the first double row ball bearing10, a contact angle of the row of balls15and a contact angle of the row of balls16have a same direction. In other words, a line of action γ1in accordance with the contact angle of the row of balls15and a line of action γ2in accordance with the contact angle of the row of balls16face each other in a such a direction that an angle θ1(not shown) made by the lines of action γ1and γ2is 0° or an acute angle (0°≦θ1≦90°). Such a constitution is adopted so that a preload is imparted to the both rows of balls15and16in a same direction (in the present case, direction from the pinion-gear side toward the counter-pinion-gear side). Further, the lines of action γ1and γ2are tilted in such a direction that outer-diameter sides thereof are on the counter-pinion-gear side and inner-diameter sides thereof are on the pinion-gear side with respect to a thrust surface. To be brief, the lines of action γ1and γ2are tilted in the upper-right direction inFIG. 2andFIG. 3. The retainers19and20retain balls17and18respectively constituting the rows of balls15and16at a position with circumferentially equal interval.

The pinion shaft17is inserted through the first inner ring13, and an end surface of the first inner ring13abuts an end surface of the pinion gear6from the axial-center direction. The first inner ring13is sandwiched from the axial-center direction between the end surface of the pinion gear6and a plastic spacer23externally mounted on the shaft part9of the pinion shaft7at an intermediate position thereof for setting the preload.

In the first double row ball bearing10, a diameter of the ball17in the large-diameter-side row of balls15and a diameter of the ball18in the small-diameter-side row of balls16are equal to each other, while pitch circle diameters D1and D2of the respective rows of balls15and16are different to each other. More specifically, the pitch circle diameter D1of the large-diameter-side row of balls15is set to a value larger than that of the pitch circle diameter D2of the small-diameter-side row of balls16. As described, the first double row ball bearing10has a double row structure (rows of balls15and16) in which the two rows of balls have the different pitch circle diameters D1and D2each other.

As shown in an enlarged view ofFIG. 3, the balls17of the large-diameter-side row of balls15are placed so as to space at a predetermined radial clearance1between the large diameter outer ring raceway11aand the large diameter inner ring raceway13ain an initial state before assembling into the differential device. The balls18of the small-diameter-side row of balls16are placed so as to space at a predetermined radial clearance β1smaller than the radial clearance α1(α1>β1) between the small diameter outer ring raceway11band the small diameter inner ring raceway13bin the initial state before assembling into the differential device.

The second double row ball bearing25is an oblique contact double row ball bearing, and comprises a single second outer ring12fitted to an inner peripheral surface of the annular wall27B and a second assembly component22. The second assembly component22is assembled into the second outer ring12from the counter-pinion-gear side toward the pinion-gear side along the axial-center direction.

The second outer ring12has a structure of a counterbored outer ring. More specifically, the second outer ring12comprises a small diameter outer ring raceway12aon the pinion-gear side and a large diameter outer ring raceway12bon the counter-pinion-gear side. A planar part12cis formed between the small diameter outer ring raceway12aand the large diameter outer ring raceway12b. The planar part12chas a diameter larger than that of the small diameter outer ring raceway12band continuous to the large diameter outer ring raceway12a. Accordingly, an inner peripheral surface of the second outer ring12is thus formed in the stepwise shape.

The second assembly component22comprises a single second inner ring14, a small-diameter-side row of balls28, a large-diameter-side row of balls29, and retainers32and33. The second inner ring14has a structure of a counterbored inner ring. More specifically, the second inner ring14comprises a small diameter inner ring raceway14aand a large diameter inner ring raceway14b. The small diameter inner ring raceway14afaces the small diameter outer ring raceway12ain a radial direction. The large diameter inner ring raceway14bfaces the large diameter outer ring raceway12bin a radial direction. A planar part14cis formed between the small diameter inner ring raceway14aand the large diameter inner ring raceway14b. The planar part14chas a diameter smaller than that of the large diameter inner ring raceway14band continuous to the small diameter inner ring raceway14a. An outer peripheral surface of the first inner ring14is thus formed in the stepwise shape.

The pinion shaft7is inserted through the second inner ring14. The second inner ring14is sandwiched from the axial-center direction between the plastic spacer23for setting the preload and a shield37.

The small-diameter-side row of balls28are placed to fit on the pinion-gear side, that is, between the small diameter outer ring raceway12aand the small diameter inner ring raceway14a. The large-diameter-side row of balls29are placed to fit on the counter-pinion-gear side, that is, between the large diameter outer ring raceway12band the large diameter inner ring raceway14b.

In the second double row ball bearing25, a contact angle of the row of balls28and a contact angle of the row of balls29have a same direction. In other words, a line of action γ3in accordance with the contact angle of the row of balls28and a line of action γ4in accordance with the contact angle of the row of balls29face each other in a such a direction that an angle θ2(not shown) made by the lines of action γ3and γ4is 0° or an acute angle (0°≦θ2<90°). Such a constitution is adopted so that the preload is imparted to the both rows of balls28and29in a same direction (in the present case, direction from the counter-pinion-gear side toward the pinion-gear side). Further, the lines of action γ3and γ4are tilted in such a direction that outer-diameter sides thereof are on the pinion-gear side and inner-diameter sides thereof are on the counter-pinion-gear side with respect to the thrust surface. To be brief, the lines of action are tilted on the downside inFIGS. 2 and 3. The retainers32and33retain balls30and31respectively constituting the rows of balls28and29at a position with circumferentially equal intervals.

Thus, the inner-diameter sides of the lines of action γ1and γ2of the first double row ball bearing10are on the pinion-gear side with respect to the thrust surface, while the outer-diameter sides of the lines of action γ3and γ4of the second double row ball bearing25are on the pinion-gear side with respect to the thrust surface, so that the gradients of the lines of action in accordance with the contact angles of the bearings10and25are thereby reverse to each other. Such a constitution is adopted in order to reverse the directions where the preload is imparted in the bearings10and25.

In the second double row ball bearing25, a diameter of the ball30in the small-diameter-side row of balls28and a diameter of the ball31in the large-diameter-side row of balls29are equal to each other, while pitch circle diameters D3and D4of the respective rows of balls28and29are different to each other. More specifically, the pitch circle diameter D3of the small-diameter-side row of balls28is set to a value smaller than that of the pitch circle diameter D4of the large-diameter-side row of balls29. As described, the second double row ball bearing25has a double row structure (rows of balls28and29) in which the two rows of balls have the different pitch circle diameters D3and D4to each other.

As shown in an enlarged view ofFIG. 3, the balls30of the small-diameter-side row of balls28are placed to space at a predetermined radial clearance α2between the small diameter outer ring raceway12aand the small diameter inner ring raceway14ain the initial state before assembling into the differential device. The balls31of the large-diameter-side row of balls29are placed to space at a predetermined radial clearance β2smaller than the radial clearance α2(α2>β2) between the large diameter outer ring raceway12band the large diameter inner ring raceway14bin the initial state before assembling into the differential device.

An oil-circulating path40is formed between an outer wall of the front case3and one side of the annular wall27A. An oil inlet41of the oil circulating path40is opened toward a ring-gear-8side of the oil circulating path40, while an oil outlet42of the oil circulating path40is opened toward between the annular walls27A and27B.

The differential device1comprises a companion flange43. The companion flange43comprises a barrel part44and a flange part45formed as united with the barrel part44.

The barrel part44is externally mounted on the shaft part9of the pinion shaft7on the other side thereof, namely, on a drive-shaft side (not shown) thereof. The shield37is interposed between an end surface of the barrel part44and an end surface of the second inner ring14of the second double row ball bearing25.

An oil seal46is arranged between an outer peripheral surface of the barrel part44and an inner peripheral surface of an opening of the front case3on the other side thereof. A seal protective cap47is attached to the other-side opening of the front case3. The oil seal46is covered with the seal protective cap47. A screw part48is formed at an end part of the shaft part9on the other side thereof. The screw part48is protruded into a central recess part43aof the flange part45. A nut49is screwed into the screw part48so that the first inner ring13of the first double row ball bearing10and the second inner ring14of the second double row ball bearing25are sandwiched between the end surface of the pinion gear6and an end surface of the companion flange43in the axial-center direction. A predetermined preload is imparted to the first double row ball bearing10and the second double row ball bearing25via the shield37and the plastic spacer23.

In the differential device1thus constituted, a lubricating oil50is reserved in the differential case2at a predetermined level L in a state where the operation is halted. The lubricating oil50is raised upward by the rotation of the ring gear8when the operation starts, travels through the oil circulating path40in the front case3, and is introduced and supplied to upper parts of the first double row ball bearing10and the second double row ball bearing25. Thereby, the lubricating oil50circulates in the differential case2so as to lubricate the first double row ball bearing10and the second double row ball bearing25.

Next, a method of assembling the differential device1is described referring to a partial sectional view ofFIG. 4. In order to assemble the differential device1, the first double row ball bearing10and the second double row ball bearing25are assembled in advance. Before the first double row ball bearing10is assembled, the radial clearance β1is adjusted to be smaller than the radial clearance β1as described earlier. More specifically, the respective parts of the first double row ball bearing10are formed so as to obtain the foregoing relationship between the clearances, and further, shapes of the respective parts are adjusted so that the clearances in the predetermined state can be obtained in the assembly.

Before the second double row ball bearing25is assembled, an clearance between the small-diameter-side row of balls28, and the small diameter outer ring raceway12aand the small diameter inner ring raceway14ais adjusted so that the radial clearance β2is smaller than the radial clearance α2as described earlier. More specifically, the respective parts of the second double row ball bearing25are formed so as to obtain the foregoing relationship between the clearances, and further, shapes of the respective parts are adjusted so that the clearance in the predetermined state can be obtained in the assembly.

After the foregoing adjustments and preparations are made, the first double row ball bearing10is disassembled into the first outer ring11and the first assembly component21, and the second double row ball bearing25is disassembled into the second outer ring12and the second assembly component22. Then, the first double row ball bearing10and the second double row ball bearing25are incorporated into the differential device1. More specifically, the first outer ring11and the second outer ring12are respectively pressed into the annular walls27A and27B. More specifically, in a state where the front case3and the rear case4are still separated, the first outer ring11is incorporated into the front case3and further pressed in the axial-center direction from the one-side opening of the front case3until it abuts a step part formed on the annular wall27A. Then, the second outer ring12is pressed in the axial-center direction from the other-side opening of the front case3until it abuts a step part formed on the annular wall28B.

The first assembly component21(specifically, first inner ring13) is inserted through the pinion shaft7. Then, the first assembly component21is incorporated into the pinion shaft7so as to locate on the pinion-gear-6side of the shaft part9of the pinion shaft7.

The pinion shaft7into which the first assembly component21is incorporated is inserted through the one-side opening of the front case3from the small-diameter side thereof. At the time, the pinion shaft7is inserted so that the balls18of the small-diameter-side row of balls16of the first assembly component21are fitted into the small-diameter outer ring raceway11bof the first outer ring11. Further, the pinion shaft7is inserted so that the balls17of the large-diameter-side row of balls15are fitted into the large-diameter outer ring raceway11aof the first outer ring11. In order to realize the assembly process described above, the small-diameter-side row of balls16is arranged to be closer to a rear side in the direction where the pinion shaft7is inserted (the counter-pinion-gear side) than the large-diameter-side row of balls15.

Next, the plastic spacer23is inserted by externally fitting to the shaft part9of the pinion shaft7from the other-side opening of the front case3. Subsequently, the second assembly component22(specifically, second inner ring14) is inserted by externally fitting to the shaft part9of the pinion shaft7from the other-side opening of the front case3. In order to realize the foregoing insertion by externally fitting, the small-diameter-side row of balls28is arranged to be closer to a rear side in the direction where the pinion shaft7is inserted (pinion-gear side) than the large-diameter-side row of balls29.

Thereafter, the shield37is inserted through the shaft part9of the pinion shaft7from the other-side opening of the front case3. Further, the oil seal46is fixed on the shaft part9of the pinion shaft7from the other-side opening of the front case3. The seal protective cap47is mounted on the other-side opening of the front case3. The barrel part44of the companion flange43is inserted through the seal protective cap47so that the end surface of the barrel part44abuts the shield37. Then, the nut49is screwed into the screw part48. Thereby, a thrust load is imparted to the first double row ball bearing10and the second double row ball bearing25, and a predetermined preload is imparted thereto. The direction to impart the preload id done as below. The preload is imparted to the first double row ball bearing10along the direction from the pinion-gear side toward the counter-pinion-gear side, while the preload is imparted to the second double row ball bearing25along the direction from the counter-pinion-gear side toward the pinion-gear side. Thus, the preload is imparted to the first and second double row ball bearings10and25in the reverse directions.

In the differential device1, the radial clearance β1is set to a value smaller than that of the radial clearance α1. Therefore, when the thrust load for imparting the preload is applied to the first double row ball bearing10, the balls18of the small-diameter-side row of balls16are fitted into the raceways11band13bat the predetermined contact angle before the balls17of the large-diameter-side row of balls15are fitted into the raceways11band13b, and thereby the rotation torque is generated.

In the same way, in the differential device1, the radial clearance β2is set to a value smaller than that of the radial clearance α2in a similar manner. Therefore, when the thrust load for imparting the preload is applied to the second double row ball bearing25, the balls31of the large-diameter-side row of balls29are fitted into the raceways12band14bat the predetermined contact angle before the balls30of the small-diameter-side row of balls28are fitted into the raceways12aand14a, and thereby the rotation torque is generated.

In the first double row ball bearing10and the second double row ball bearing25, the initial rotation torques are obtained as described, and the larger thrust load which is further applied so that the preload at a necessary level is applied. Explanation is given below.

In the state where the initial rotation torques are generated, as described, the radial clearance β1, that is on the side of the smaller clearance, is reduced, and the balls18of the small-diameter-side row of balls16, the small diameter outer ring raceway11band the small diameter inner ring raceway13bare thereby already fitted with respect to one another at the predetermined contact angle in the first double row ball bearing10, while the radial clearance β2, that is on the side of the smaller clearance, is reduced so that the balls31of the large-diameter-side row of balls29and the raceways12band14bare fitted with respect to one another at the predetermined contact angle in the second double row ball bearing25.

When the thrust load is further imparted to the first double row ball bearing10and the second double row ball bearing25in the described state, the radial clearance α1, that is on the side of the larger clearance, is reduced so that the balls17of the large-diameter-side row of balls15and the raceways11aand13aare fitted with respect to one another at the predetermined contact angle in the first double row ball bearing10, and thereby the rotation torque is generated. In a similar manner, the radial clearance α2, that is on the side of the larger clearance, is reduced so that the balls30of the small-diameter-side row of balls28and the raceways12aand14aare fitted with respect to one another at the predetermined contact angle in the second double row ball bearing25, and thereby the rotation torque is generated.

By slightly shifting the fitting timing in the respective rows of balls as described, the rotation torque is selectively obtained in the row of balls16alone in the first double row ball bearing10, and thereafter the rotation torque resulting from the synthesized rotation torques of the rows of balls15and16is obtained with a time lag. In a similar manner, in the second double row ball bearing25, the rotation torque is selectively obtained in the row of balls29alone, and thereafter the rotation torque resulting from the synthesized rotation torques of the rows of balls28and29is obtained with a time lag. Accordingly, a maximum rotation torque thereby obtained is increased, which expands the range of the adjustable torque. The adjustment range of the preload to be set is thereby increased, and the preload control is consequently facilitated.

A graph ofFIG. 4shows a relationship between the thrust load S (preload) imparted to the oblique contact double row ball bearing and the rotation torque T corresponding to the thrust load S. The thrust load applied to the oblique contact double row ball bearing can be known through the measurement of the rotation torque T.

In the drawing, a broken line60shows a result of the conventional oblique contact double row ball bearing (double row ball bearing in which the pitch circle diameters of the respective rows are different to each other), while a solid line61shows a result of the first and second oblique contact double row ball bearings10and25according to the present invention (oblique contact double row ball bearings in which the pitch circle diameters of the respective rows are different to each other). Comparing a tilt of the broken line60to that of the solid line61to each other, the tilt of the solid line61is larger than that of the broken line60. A reason is described below.

As described, in the first double row ball bearing10, the balls18of the small-diameter-side row of balls16and the raceways11band13bare first fitted with respect to one another so that the initial rotation torque is generated, and thereafter, the balls17of the large-diameter-side row of balls15and the raceways11aand13aare fitted with respect to one another so that the rotation torque is further generated.

In a similar manner, in the second double row ball bearing25, the balls31of the large-diameter-side row of balls29and the raceways12band14bare first fitted with respect to one another so that the initial rotation torque is generated, and thereafter, the balls30of the small-diameter-side row of balls28and the raceways12aand14aare fitted with respect to one another so that the rotation torque is further generated.

As a result, the rotation torque can be largely set and the range of the torque to be set can be increased in comparison to the conventional oblique contact double row ball bearing in which the balls of the both rows are simultaneously fitted into the raceways, and the gradient of the full line61is larger than that of the broken line60.

Description is given here, for example, to a case where it is tried to obtain the “S2” value as the thrust load S referring to a graph shown inFIG. 5. Because the tilt of the solid line61is larger than that of the broken line60, the adjustment range of the rotation torque T corresponding to the “S2” value is T1in the broken line60(conventional example), while the adjustment rage of the rotation torque T is T2in the first and second double row ball bearings10and25according to the present invention, that is, it is T2>T1. Therefore, when the thrust load S2is applied so that the same preload is obtained, the range for the adjustment is larger in the first and second double row ball bearings10and25according to the present invention than in the conventional oblique contact double row ball bearing. As a result, the preload can be accurately and easily applied.

Consideration is done about a case where the thrust load “S2” to be imparted is in the range from “S1” through “S3” in terms of its tolerance. In this case, the adjustment range of the rotation torque T in the conventional oblique contact double row ball bearing is T3, while the adjustment range of the rotation torque T is T4in the first and second double row ball bearings10and25according to the present invention, that is, it is T4>T3as shown inFIG. 5. Thus, even in this case, the first and second double row ball bearings10and25according to the present invention can achieve the adjustment range wider than that of the conventional double row ball bearing when it is tried to obtain the same preload. As a result, the thrust load S (preload) can be accurately and easily applied.