Double row ball bearing

In the double row ball bearing, a plurality of balls are incorporated into a space between a first inner race raceway of an inner race and a first outer race raceway of an outer race, a plurality of balls are incorporated into a space between a second inner race raceway of the inner race and a second outer race raceway of the outer race, there is formed a counterbore portion at least in the outer race raceway of a pair of one-row side inner and outer race raceways, and the balls are incorporated in a maximum manner into a space between the pair of inner and outer race raceways which are so arranged as to include the outer race with the counterbore portion formed therein, to thereby make it possible to provide a double row ball bearing in which the rated load of one-row side raceway thereof can be selected up to its maximum with respect to the outside diameter dimension of an outer race thereof, and an excellent fatigue life can be attained.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a ball bearing and, in particular, to a
 double row ball bearing suitable for use in an engine cooling water pump
 in which raceways capable of holding balls are of a double row type and a
 counter bore is formed in one of two raceways of an outer race. Also, the
 present invention relates to an improvement in the endurance of the double
 row ball bearing.
 2. Description of the Related Prior Art
 FIG. 5 is a partially longitudinal section view of a conventional-type
 water pump double row ball bearing 30 suitable for use in a water pump
 which is used to circulate a coolant for an engine of a car. This type of
 double row ball bearing is disclosed in, for example, Japanese Patent
 Unexamined Publication No. Hei. 9-22212.
 In FIG. 5, in a rotary shaft 31 which corresponds to an inner race, there
 are formed a first inner race raceway 32 consisting of a groove and a
 second inner race raceway 33 also consisting of a groove in such a manner
 that they respectively extend over the whole circumferential direction of
 the outer peripheral portion of the rotary shaft 31.
 On the other hand, in the inner peripheral portion of a substantially
 cylindrical-shaped outer race 34, there are formed a first outer race
 raceway 37, which is composed of a groove 35 and a counterbore portion 36
 having a linear-shaped cross section, and a second outer race 38 composed
 of a groove 38 in such a manner that they respectively extend over the
 whole circumferential direction of the inner peripheral portion of the
 outer race 34.
 The outer race 34 is disposed in such a manner that the center line C
 thereof is identical with the center line C' of the rotary shaft 31, the
 first inner race raceway 32 is opposed to the first outer race raceway 37,
 and the second inner raceway 33 is opposed to the second outer race
 raceway 38. Also, the shapes and clearances of the first and second
 raceways are selected in such a manner that they substantially correspond
 to the shapes of balls 39 to be incorporated between the corresponding
 raceways and also the ball 39 incorporated between the corresponding
 raceways are allowed to roll freely there.
 The balls 39 are incorporated between the pair of first inner and outer
 race raceways in the following manner. That is, a plurality of balls 39
 are incorporated around the circumferential direction of the first inner
 and outer race raceways, in more detail, in a so called maximum manner in
 which as many balls 39 as possible can be incorporated. By the way, the
 balls 39 are uniformly distributed at a predetermined interval in the
 circumferential direction thereof and can be held by a tilt-type retainer
 40.
 On the other hand, between the second inner and outer raceways, there are
 incorporated balls 41 in the following manner. That is, a plurality of
 balls 41 are incorporated around the circumferential direction of the
 second inner and outer raceways, in more detail, the balls 41 are
 incorporated in a proper number which is smaller than the number of balls
 39 to be incorporated into and between the pair of first inner and outer
 raceways. By the way, the balls 41 can be uniformly distributed at a
 predetermined interval in the circumferential direction thereof and can be
 held by a retainer 42.
 On the two end portions of the outer race 34 in the center line direction
 thereof, there are disposed sealing devices 43 and 44 in order not only to
 prevent leakage of bearing lubricant but also to prevent invasion of
 liquid into the bearing from the outside. Thus, the portions of the ball
 bearing 30 where the balls 39 and 41 are incorporated are sealed against
 the outside by the sealing devices 43 and 44.
 The thus structured ball bearing has an advantage that, since the formation
 of the counterbore portion can increase the number of balls to be
 incorporated into one row of raceways thereof, the resistance of the
 present raceways to a radial load can be increased.
 By the way, as known well, generally, a rolling bearing is roughly
 classified into a ball bearing and a roller bearing according to the kinds
 of rolling elements used. And, normally, there is a tendency that the
 roller bearing has larger resistance to a rated radial load (which is
 hereinafter referred to as a rated load) in the axial direction than the
 ball bearing. Therefore, in the above-mentioned double row ball bearing
 for a water pump, use of rollers as the rolling elements thereof is
 preferable from the viewpoint of enhancement in the rated load.
 However, when the roller is used as the rolling element, if the rotary
 shaft is inclined relatively to the outer race, then there is applied an
 excessive load (which is referred to an edge load) onto and between the
 end edges of the rolling surfaces of the respective rollers and the outer
 and inner races, which lowers the fatigue life of the inner and outer
 races. And, the narrower the width of the outer race is, the easier the
 edge load is to occur. This deteriorates the ratio of the actual life of
 the outer race to the calculated life thereof. Therefore, it can be
 concluded that, especially when the outer race has a short pitch, it is
 not preferable to use the roller as the rolling element of the rolling
 bearing.
 Thus, it is necessary to employ a double row bearing which uses balls as
 rolling elements thereof. In this case, as in the water pump double row
 ball bearing shown in FIG. 5, there may be employed a structure in which a
 counterbore portion is formed in one of the two outer race raceways to
 thereby increase the number of balls to be incorporated into the present
 outer race raceway and thus increase the rated load of that portion.
 However, there is a limit to the size of the ball used as the rolling
 element. For example, even when the number of balls can be increased, if
 the diameter of each ball is not large to a certain degree, it is
 impossible to achieve a satisfactory rated load. On the other hand, when
 the ball diameter is excessively large, the number of balls that can be
 incorporated decreases, which also deteriorates the rated load of the
 bearing. Therefore, with employment of this structure, a condition for the
 replacement of the roller by the ball cannot be satisfied.
 SUMMARY OF THE INVENTION
 The present invention aims at eliminating the drawbacks found in the
 above-mentioned conventional double row ball bearings. Accordingly, it is
 an object of the invention to provide a double row ball bearing which can
 be used under a high-speed rotation condition and also in which the rated
 load of one row side raceways of the double row raceways thereof can be
 selected up to its maximum with respect to the outside diameter dimension
 of an outer race thereof or with respect to the raceway diameter dimension
 of the outer race and also an excellent fatigue life can be attained.
 The above object can be achieved by a double row ball bearing, according to
 the invention , comprising:
 an inner race having first and second inner race raceways on its outer
 peripheral surface; an outer race having first and second outer race
 raceways on its inner peripheral surface; and a plurality of freely
 rolling balls respectively incorporated into a space between the first
 inner race raceway of the inner race and the first outer race raceway of
 the outer race as well as into a space between the second inner race
 raceway of the inner race and the second outer race raceway of the outer
 race,
 wherein the number of balls to be incorporate into a space between the pair
 of first outer race raceway and first inner race raceway is different from
 the number of balls to be incorporated into a space between the pair of
 second outer race raceway and second inner race raceway; and,
 in one of the outer race raceways, which is located on one row side where a
 larger number of balls are incorporated, there is formed a counterbore
 portion, and, into a space between the pair of inner and outer race
 raceways so arranged as to include the outer race raceway with the
 counterbore portion formed therein, the balls are incorporated in a
 maximum manner,
 wherein the diameter of balls to be incorporated into a space between the
 pair of inner and outer race raceways including the outer race raceway
 with the counterbore portion formed therein is 22%-25% of the outside
 diameter dimension of the outer race.
 According to the invention as set forth in the present invention, since the
 diameter of balls is 22%-25% of the outside diameter dimension of the
 outer race, the rated load value can be selected up to its maximum with
 respect to the outside diameter of the outer race and thus an excellent
 fatigue life can be attained. And, because the balls are used as the
 rolling elements of the bearing, not only the lubrication life of the
 bearing is long but also, even if the outer race thereof is a short-pitch
 product, there is no fear for occurrence of an edge load.
 In addition, the above-mentioned object can also be achieved by a double
 row ball bearing, according to the present invention, comprising:
 an inner race having first and second inner race raceways on its outer
 peripheral surface, an outer race having first and second outer race
 raceways on its inner peripheral surface, and a plurality of freely
 rolling balls respectively incorporated into a space between the first
 inner race raceway of inner race and the first outer race raceway of the
 outer race as well as into a space between the second inner race raceway
 of the inner race and the second outer race raceway of the outer race,
 wherein the number of balls to be incorporate into a space between the pair
 of first outer race raceway and first inner race raceway is different from
 the number of balls to be incorporated into a space between the pair of
 second outer race raceway and second inner race raceway; and,
 in one of the outer race raceways, which is located on one row side where a
 larger number of balls are incorporated, there is formed a counterbore
 portion, and, into a space between the pair of inner and outer race
 raceways so arranged as to include the outer race raceway with the
 counterbore portion formed therein, the balls are incorporated in a
 maximum manner,
 wherein the diameter of balls to be incorporated into a space between the
 pair of inner and outer race raceways including the outer race raceway
 with the counterbore portion formed therein is 25%-28% of the outer race
 raceway diameter dimension of the outer race.
 According to the ball bearing according to the present invention, since the
 diameter of balls is 25%-28% of the raceway diameter of the outer race,
 the rated load value can be selected up to its maximum with respect to the
 raceway diameter dimension of the outer race and thus an excellent fatigue
 life can be attained. And, because the balls are used as the rolling
 elements of the bearing, not only the lubrication life of the bearing is
 long but also, even if the outer race thereof is a short-pitch product,
 there is no fear for occurrence of an edge load.
 The present disclosure relates to subject matter contained in Japanese
 Patent Applications Nos. Hei. 10-326946 filed on Nov. 17, 1998, Hei.
 11-197891 filed on Jul. 12, 1999 and Hei. 11-267545 filed on Sep. 21,
 1999, and which is expressly incorporated herein by reference in its
 entirety.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Now, description will be given below in detail of an embodiment of a double
 row ball bearing according to the invention with reference to the
 accompanying drawings. FIG. 1 is a partially longitudinal section view of
 an outer race 1 employed in the double row ball bearing according to the
 embodiment of the invention. However, to make a clear contrast with a
 conventional type bearing, the outer race 1 is assumed that it has a shape
 which can correspond to the outer race of the above-mentioned conventional
 bearing shown in FIG. 5. In the present embodiment, the remaining portions
 thereof that are not described herein are the same as those employed in
 the above-mentioned conventional bearing.
 Also, first and second outer race raceways 2 and 3, which are portions for
 forming raceways for the rolling elements of the bearing, are designed in
 such a manner that they correspond to the diameters of balls to be
 incorporated into the first and second outer race raceways 2 and 3. In the
 present embodiment, into the first outer race raceway 2, there are
 incorporated balls 4 each having a diameter of d. By the way, it is not
 always necessary that the diameter of a ball to be incorporated into the
 first outer race raceway 2 is equal to the diameter of a ball to be
 incorporated into the second outer race raceway 3. Also, in the present
 embodiment, as shown in FIG. 5, a contact angle .alpha. is given to each
 row. This increases a position of an operating point, which makes it
 possible to gain an ascendancy over a moment load to be applied to the
 bearing.
 Now, FIG. 2 is a partially longitudinal section view of a tester 10 for
 testing the fatigue life of a double row bearing 11. On account of testing
 convenience, it is necessary to use double row bearings which are
 different in the diameter of balls employed therein. Therefore, of course,
 the double row bearing 11 can be removed from the tester 10.
 As can be seen clearly from FIG. 2, an outer race 1 of the double row
 bearing 11 is fitted with a housing 14 mounted on a hold base 13, while a
 rotary shaft 12 corresponding to an inner race, in one end portion
 thereof, is fitted with the inner surface of an auxiliary rotary body 16
 supported on an auxiliary bearing 15 which is a split-type double row
 bearing. Thus, the rotary shaft 12 can be rotated together with the
 auxiliary rotary body 16. Also, the auxiliary rotary body 16 is formed in
 a substantially cylindrical shape which extends in the longitudinal
 direction thereof in FIG. 2: one end of the auxiliary rotary body 16, as
 described above, is combined with the inner race of the auxiliary bearing
 15 and rotary shaft 12; and, the other end thereof is connected to a drive
 pulley 17 which serves as a rotation drive source in the present tester
 10. Further, on the periphery of the housing 14, there are equipped
 heating apparatus 18 and a thermocouple 19 which are respectively used to
 control temperature conditions during testing.
 The auxiliary bearing 15, in particular, an outer race thereof is fitted
 with a support body 20. On the support body 22, there is disposed tracting
 mechanism 21 which is to be connected to a load transmission member 22.
 The loading position of a load Fr given by the tracting mechanism 21 in
 the longitudinal direction thereof is set in such a manner that its offset
 distance from the end portion of the outer race 1 provides 12 mm.
 The thus structured tester 10 is now started to conduct a test on the
 double row bearing as to the fatigue life thereof. That is, at first, a
 drive source (not shown) drives the drive pulley 17 to thereby rotate the
 rotary shaft 12. Referring here to the loading method of the load Fr,
 originally, a belt load due to the tensile force of a pulley belt 23 is to
 be applied to the rotary shaft of a double row rolling bearing for a water
 pump; however, in the present tester 10, to control the value of the belt
 load, the load Fr is applied by the tracting mechanism 21, load
 transmission member 22, and a load generator device 25. In other words,
 the load generator device 25 moves the vicinity of the force point end 26
 of the load generator device 25 in the downward direction in FIG. 2 to
 thereby rotate the load transmission member 22 about a fulcrum portion 24,
 whereby an operating point portion 27 is moved in the downward direction
 in FIG. 2 and thus the load Fr directed in the downward direction in FIG.
 2 can be applied to the tracting mechanism 21 mounted on the operating
 point portion 27. And, a load is applied through a support body 20 to the
 auxiliary bearing 15 and, in response to this, the load Fr is applied to
 the auxiliary rotary body 17, whereby loads are respectively applied to
 the rotary shaft 12, balls and raceways of the double row bearing 11.
 Now, FIGS. 3 and 4 respectively show results which are obtained when a test
 has been conducted on the double row bearing 11 using the tester 10 shown
 in FIG. 2. The test is conducted under the following condition: that is,
 the highest rotation number is 6000 rpm, the highest temperature of the
 tester is 100.degree. C., and the maximum value of the load Fr is 200 kgf.
 And, as described above, the offset distance of the loading position from
 the outer race is 12 mm, an unbalance amount is 40g, and the offset
 distance of an unbalance position is 60 mm.
 Also, referring to the double row bearing 11 to be set on the tester 10, in
 the case of a test shown in FIG. 3, the outside dimensions of the outer
 race 1 are such that outer race length x =38.89 mm and outer race outside
 diameter y =35.00 mm; and, for balls to be incorporated into the
 above-mentioned first outer race raceway 2, there are prepared balls which
 are different in the diameter d from one another in the number that
 corresponds to the number of balls to be measured or tested. And, in the
 case of a test shown in FIG. 4, the outside dimensions of the outer race 1
 are such that outer race length x =38.89 mm and outer race raceway
 diameter De =31.372 mm; and, for balls to be incorporated into the
 above-mentioned first outer race raceway 2, there are prepared balls which
 are different in the diameter d from one another in the number that
 corresponds to the number of balls to be measured or tested. By the way,
 in the test shown in FIG. 4, the thickness of the outer race (thickness
 =(outside diameter -outer race raceway diameter) /2 is set to the smallest
 thickness that can stand the load. Also, in common with the two tests, the
 highest value of the load Fr is set at 200 kgf. Also, in the tests
 respectively shown in FIGS. 3 and 4, the first outer race raceway 2 shown
 in FIG. 1 is arranged on the drive side (that is, on the pulley 17 side).
 At first, description will be given below of FIG. 3. In FIG. 3, its
 horizontal axis represents a ratio of the ball diameter dimension of balls
 to be incorporated into the first outer race raceway 2 to the outside
 diameter dimension of the outer race (which is hereinafter referred to as
 a ratio of ball diameter/outer race outside diameter), and its vertical
 axis represents the endurance time (unit hr) of the bearing. In FIG. 3,
 L.sup.10 =425 hr means the endurance times, that is, the so called rated
 lives with a reliability of 90% of rolling bearings respectively using
 balls and rollers in combination that are obtained when they are set in
 the tester 10 and tested or measured by the tester 10 under the same test
 conditions.
 Next, description will be given below of the results of the test conducted
 on these rolling bearings by the tester 10. The plotting of the measured
 values is given using at least two measured values with respect to the
 same test condition and the same ratio of ball diameter/outer race outside
 diameter. The reason for this is as follows: that is, even if bearings
 looking seemingly the same are rotated under the same external condition,
 the fatigue lives thereof vary to a considerable degree; and, therefore,
 several measured values must be compared with one another to obtain a
 reliable value.
 For the ratios of ball diameter/outer race outside diameter in the range of
 0.15-0.22, the endurance times corresponding to these ratios are approx.
 190-680 hrs. Referring to this results, in some cases, there is obtained a
 better result than a bearing using balls and rollers in combination, but
 the thus obtained value is not a stable value; and much less, even under
 the same ratio of ball diameter/outer race outside diameter condition, the
 results vary in the range of 300 hrs. and, in some cases, the obtained
 value falls below 425 hrs. That is, for the ratios of ball diameter/outer
 race outside diameter in the range of 0.15-0.22, there cannot be obtained
 such values that can be used practically. This also applies similarly to
 the ratios of ball diameter/outer race outside diameter that exceed 0.25.
 Accordingly, let us turn our attention to the ratios of ball diameter/outer
 race outside diameter in the range of 0.22 -0.25. It is true that, even in
 this range, the measured values obtained under the same condition vary,
 but the variation in this range is smaller than those in the other ranges,
 and, moreover, when compared with the endurance time, L.sup.10 =425 hrs.,
 of the bearing of a type using balls and rollers in combination, there can
 be attained a sufficiently long endurance time. Thus, it can be well said
 that the measured values in this range are sufficiently practicable
 values.
 Therefore, in designing a double row rolling bearing for a water pump, if
 the diameters of balls to be incorporated into the rolling element raceway
 on the drive side or on the side where a radial load or a moment load is
 applied more than the remaining sides, that is, the diameters of balls to
 be incorporated into the raceway side where the balls are incorporated in
 a maximum manner are in the range of ball diameter/outer race outside
 diameter ratios of 0.22-0.25 (22%-25%), it is possible to supply a bearing
 which provides not only sufficient load resistance but also a sufficient
 fatigue life. And, since the balls are used as the rolling elements of the
 bearing, the bearing can provide a long lubrication life and also, even if
 the outer race thereof is a short-pitch product, there is no fear for
 occurrence of the edge load.
 Next, description will be given below of FIG. 4. In FIG. 4, its horizontal
 axis represents a ratio of the ball diameter dimension of balls to be
 incorporated into the first outer race raceway 2 to the outer race raceway
 diameter dimension of the outer race (which is hereinafter referred to as
 a ratio of ball diameter/outer race raceway diameter), and its vertical
 axis represents the endurance time (unit hr) of the bearing.
 Then, description will be given below of the results of the test conducted
 on these rolling bearings by the tester 10. For the same reason as in the
 test in FIG. 3, the plotting of the measured values is given using at
 least two measured values with respect to the same test condition and the
 same ratio of ball diameter/outer race raceway diameter.
 For the ratios of ball diameter/outer race raceway diameter in the range of
 0.17-0.25, the endurance times corresponding to these ratios are approx.
 190-680 hrs. Referring to this results, in some cases, there is obtained a
 better result than a bearing using balls and rollers in combination, but
 the thus obtained value is not a stable value; and much less, even under
 the same ball diameter/outer race outside diameter condition, the results
 vary in the range of 300 hrs. and, in some cases, the obtained value falls
 below 425 hrs. That is, for the ratios of ball diameter/outer race outside
 diameter in the range of 0.17-0.25, it is not possible to obtain such
 values that can be used in practical cases. This also applies similarly to
 the ratios of ball diameter/outer race raceway diameter that exceed 0.28.
 Accordingly, let us turn our attention to the ratios of ball diameter/outer
 race raceway diameter in the range of 0.25 -0.28. Even in this range, the
 measured values obtained under the same condition truly vary, but the
 variation in this range is smaller than those in the other ranges, and,
 moreover, when compared with the endurance time, L.sup.10 =425 hrs., of
 the bearing of a type using balls and rollers in combination, there can be
 attained a sufficiently long endurance time. Thus, it can be well said
 that the measured values in this range can be used as sufficiently
 practicable values.
 Therefore, in designing a double row rolling bearing for a water pump, if
 the diameters of balls to be incorporated into the rolling element raceway
 on the drive side or on the side where a radial load or a moment load is
 applied more than the remaining sides, that is, the diameters of balls to
 be incorporated into the raceway side where the balls are incorporated in
 a maximum manner are in the range of ball diameter/outer race raceway
 diameter ratios of 0.25-0.28 (25%-28%), it is possible to supply a bearing
 which provides not only sufficient load resistance but also a sufficient
 fatigue life. And, since the balls are used as the rolling elements of the
 bearing, the bearing can provide a long lubrication life and also, even if
 the outer race thereof is a short-pitch product, there is no fear for
 occurrence of the edge load.
 By the way, the present invention is not limited to the above-mentioned
 embodiments but various changes and improvements are also possible. For
 example, the invention can also apply to other double row bearings which
 are requested to have equivalent performance to a bearing for a water pump
 with respect to high-speed rotation and/or high load. Also, the invention
 can further apply to a double row bearing using an outer race which is not
 a short-pitch product.
 As has been described heretofore, in a double row bearing according to the
 invention, since the diameter dimension of balls to be incorporated into a
 raceway including a counterbore portion is in the range of 22%-25% of
 outer race outside diameter dimension or in the range of 25%-28% of outer
 race raceway diameter dimension, the rated load of the bearing can be set
 at its maximum value with respect to the outer race dimension and also an
 excellent fatigue life can be provided. Further, since the balls are used
 as the rolling elements of the bearing, the bearing can enjoy a long
 lubrication life and, even if the outer race of the bearing is a
 short-pitch product, there is no fear for occurrence of an edge load.
 While there has been described in connection with the preferred embodiment
 of the invention, it will be obvious to those skilled in the art that
 various changes and modifications maybe made therein without departing
 from the invention, and it is aimed, therefore, to cover in the appended
 claim all such changes and modifications as fall within the true spirit
 and scope of the invention.