Method of measuring preload clearance in double row rolling bearing and apparatus therefore

A method of measuring the preload clearance in a double row rolling bearing. The method includes the steps of fixing the outer end face of the first inner ring in position while subjecting the outer end face of the second inner ring to a first load in a direction which moves the second inner ring toward the first inner ring at a relatively smaller constant amount so as not to reduce the preload clearance to zero, and obtaining a value H.sub.1 corresponding to the position of the outer end face of the second inner ring. Fixing the outer end face of the first inner ring in position while subjecting the outer end face of the second inner ring to a second load in a direction which moves the second inner ring toward the first inner ring at a relatively larger, constant amount enough to reduce the preload clearance to zero and obtaining the value H.sub.2 corresponding to the position of the outer end face of the second inner ring. Then calculating the difference between the value H.sub.1 and the value H.sub.2 thereby providing a displacement amount, and obtaining the preload clearance from the displacement amount based on a predetermined relationship between the displacement amount and the preload clearance.

FIELD OF THE INVENTION 
The present invention is related to a process end apparatus to measure a 
preload clearance in a double row rolling bearing, which are utilized to 
measure the size of the preload clearance provided to preload the double 
row rolling bearing upon rotatably support a vehicle wheel. 
A double row rolling bearing used to support a vehicle wheel in a 
suspension apparatus comprises, as shown in FIG. 1, an outer ring or race 
1 having outer raceways 2 in double rows on its inner peripheral surface, 
a pair of inner ring or race 3a, 3b concentric with the outer ring or race 
1 on the inside of the outer ring or race 1 and having an inner raceway on 
their outer peripheral surfaces, respectively, and a plurality of rolling 
members 5 provided between the inner raceways 4 and the outer raceways 2, 
respectively. The outer race or ring 1 is supported by a suspension 
apparatus (not shown for installation in the vehicle. 
Generally, the prior art double row rolling bearing as shown above is 
adapted to provide the rolling members 5 with a slight preload or a slight 
clearance when installed in the vehicle. And, there is no mas-productive 
double row rolling bearing having the inner rings or races 3a, 3b between 
the inner end edges of which a preload clearance is provided to preload 
the rolling members 5 by a predetermined amount. 
Recently, the double row rolling bearings for installation into vehicles 
are developed to have a preload clearance in themselves before 
installation in order to increase rigidity in the wheel bearing portion 
and reduce the weight of the wheel bearing portion and to improve driving 
performance. It is noted that the double row rolling bearing having a 
preload provided in the rolling members 5 can be given more rigidity than 
the double row rolling bearing without such a preload. 
Accordingly, the bearing manufacturers are requested by the automobile 
manufacturers to provide the bearings themselves with a slight preload 
clearance in the stage of bearing production and to guarantee the 
precision of the preload clearance. 
In the double row rolling bearing of FIG. 1, the rolling members 5 are 
preloaded before installation into the vehicle by regulating the outer 
ring 1, inner rings 3a, 3b and rolling members 5 in size so that the inner 
end edges of the pair of inner rings 3a, 3b are abutted to each other so 
as to provide the rolling members 5 with a predetermined preload. It will 
be noted that the inner end edge of the inner ring 3a is faced to the 
inner end edge of-the inner ring 3b. 
Specifically, the pair of inner rings 3a, 3b are lightly pressed at their 
outer end faces so as to be moved toward each other so that a clearance is 
formed between the inner end edges of the inner rings 3a, 3b to have a 
width size h in the state where the rolling members 5 are lightly engaged 
with the outer raceways 2 and with the inner raceways 4. It will be noted 
that the outer end faces of the inner rings 3a, 3b are faced to the 
opposite directions. 
The inner end edges come into contact with each other when preloaded upon 
installation of the double row rolling bearing into the vehicle. In this 
state, the outer ring 1, inner rings 3a, 3b and rolling members 5 are 
elastically deformed to produce a preload. 
Accordingly, the width size h is referred to as a preload clearance for 
providing a predetermined preload. 
Incidentally, the rolling members 5 are formed in a ball shape, but can be 
formed in a tapered roll shape for use in a hub unit incorporated in a 
heavy vehicle. In this case, the raceways 2 and 4 have a linear cross 
sectional shape. 
Anyhow, it is important to provide a double row rolling bearing and the 
vehicle with such a double row rolling bearing with the best performance 
that the preload clearance is regulated to a proper value so as to provide 
the rolling members 5 with a preload. 
If the preload clearance or preload is too small, or if a force to press 
the rolling members 5 between the raceways 2 and 4 is too small, the 
bearing rigidity would be insufficient, and in a worst case, backlash 
would be caused in the inner rings 3a, 3b to support the axle inside the 
outer ring 1. Consequently, the traveling stability of vehicle would be 
damaged or in an extreme case, abnormal noises would be produced during 
traveling. 
On the contrary, if the preload clearance or preload is too large, or if a 
force to press the rolling members 5 between the raceways 2 and 4 is too 
large, the rotation resistance would be so increased that the power 
capacity and fuel consumption performance of the vehicle would be reduced, 
or the life of the hub unit would be shortened due to the excessive face 
pressure on the rolling face of the rolling members or on the raceways. In 
the worst cases, normal operation would be impossible due to abnormal heat 
generation. 
In order to avoid any poor preload to cause various troubles as mentioned 
above, the width size h of the clearance 6 must be obtained corresponding 
to the preload clearance. If the width size obtained is displaced out of 
the proper range, the double row rolling bearing having such an improper 
width size must be thrown away, and the data are fed back to the 
processing steps of bearing parts to adjust the width size in the proper 
range. 
Such a method to measure the preload or preload clearance in the double row 
rolling bearing is disclosed in Japanese Patent First Publication KOKAI 
No. H5-256635 as follows; 
(1) In the state where the inner rings 3a, 3b are abutted at their inner 
end edges to each other under a preload, the outer ring 1 is rotated with 
reference to the inner rings 3a, 3b to obtain the rotating torque, from 
which the preload is obtained. 
(2) A spacer having a thickness T (known) in size is sandwiched between the 
inner rings 3a, 3b to obtain the axial displacement ha due to the spacer 
of the inner ring 3a, 3b with reference to the outer ring 1, from which 
the preload clearance h is obtained to be equal to T-ha. 
(3) A constant pressure fluid such as a compressed air is sent to the 
inside of the inner ring 3a, 3b assembled as shown in FIG. 1 and flowed 
out through the clearance 6 to outside, and the flow amount and back 
pressure at this moment are measured to know the width size h of the 
clearance 6, 
In the measurement of bearing preload as in Measurements (1) to (3) 
mentioned above, however, there are some problems as follows; 
In the case of Measurement (1), because the preload is not directly 
measured, the preload is not precisely obtained, 
Since the .quality precision required in the double row rolling bearing for 
use in the recent automobile industry is very severe, so that sufficient 
precision is hardly obtained in the Measurement (1). 
In Measurement (2), precise values for the preload clearance is obtained, 
but it is inconvenient and takes a long time to sandwich the spacer 
between the inner rings 3a, 3b. In addition, automation is so difficult, 
that it is impossible to measure large number of double row rolling 
bearings for the preload clearance, e.g. in the case where the whole 
number of the products are examined in situ in the manufacturing plants. 
Measurement (3) is worse in measurement precision to Measurement (2). 
Specifically, the flow amount and back pressure when the constant pressure 
fluid flows out of the clearance 6 is varied due to various causes even if 
the clearance 6 has a constant; width size h. For example, the 
temperature, humidity (water content), or cleanness, of the constant 
pressure fluid, or the width size, surface roughness, chamfering degree, 
etc. of the inner end edges of the inner rings 3a, 3b, variances of the 
clearance components etc. would cause the flow amount or back pressure to 
change in a not-negligible degree. Accordingly, sufficient precision would 
hardly be obtained. 
In addition, foreign materials such as duet can exist in the outlet port of 
the constant pressure fluid, or in the inner end edge portions of the 
inner rings 3a, 3b, and be blown by the constant pressure fluid to enter 
the interior of the bearing where the rolling members 5, outer raceways 2 
and inner raceways 4 are located. Such foreign materials entering the 
interior of the bearing would undesirably affect the bearing performance. 
SUMMARY OF THE INVENTION 
An objective of the present invention is to provide a method and apparatus 
to measure the preload clearance of the double row rolling bearing to 
overcome the problems as mentioned above. 
Another objective of the present invention is to provide a method of 
measuring the preload clearance in a double row rolling bearing which 
comprises an outer ring having outer raceways in double rows on its inner 
peripheral surface, first and second inner rings each having an inner 
raceway on its outer peripheral surface and each provided concentric with 
the outer ring, and a plurality of rolling members provided between the 
inner raceways and the outer raceways in double rows, respectively, and 
the rolling members being preloaded in the state where the first and 
second inner rings are abutted to each other at their inner end edges, and 
the method comprising the following steps (a) to (c). 
(a) The outer end face of the first inner ring is fixed in position while 
the outer end face of the second inner ring is subjected to a first load 
in a direction to move the second inner ring toward the first inner ring 
at a relatively smaller constant amount so as not to reduce the preload 
clearance to zero, and to obtain the value H.sub.1 corresponding to the 
position of the outer end face of the second inner ring. 
(b) The outer end face of the first inner ring is fixed in position while 
the outer end face of the second inner ring is subjected to a second load 
in a direction to move the second inner ring toward the first inner ring 
at a relatively larger, constant amount enough to reduce the preload 
clearance to zero, and to obtain the value H.sub.2 corresponding to the 
position of the outer end face of the second inner ring. 
(c) The difference between the value H.sub.1 in the step (a) and the value 
H.sub.2 in the step (b), that is (H.sub.2 -H.sub.1), is calculated to 
provide a displacement amount, and the preload clearance is obtained from 
the displacement amount based on a predetermined relationship between the 
displacement amount and the preload clearance. 
Another objective of-the present invention is to provide an apparatus for 
measuring the reload clearance in the double row rolling bearing which 
comprises a receiving block having a face to which the outer end face of 
the first inner ring is abutted, a retaining block having a face provided 
with a retaining face to which the outer end face of the second inner ring 
is abutted, so that a relatively smaller first load is applied to the 
second inner ring such that the first load does not reduce the preload 
clearance to zero, a pressing device for applying a predetermined load to 
the retaining block so that a relatively larger second load which is 
sufficient to reduce the preload clearance to zero is applied to the 
second inner ring, and a measuring device for measuring the axial position 
of the retaining block. 
In the method and apparatus for measuring the preload in the double row 
rolling bearing in the present invention, the preload clearance is easily 
and precisely obtained, and automation for measurement is possible.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is realized through experiments where a number of 
double row rolling bearings as shown in FIG. 1 are produced and a 
predetermined load is applied axially to the outer end face of the inner 
rings in each of the bearings so as obtain the relationship between the 
displacement amount of the inner ring and the preload clearance. As a 
result, it is found out that when the same amount of load is applied to 
the bearings in the same series, that is the bearings produced in the same 
model number and in the same dimensions in design, the displacement amount 
and the preload clearance are substantially placed in a proportional 
relationship to each other above. 
While a preload clearance exists between the inner end edges of the pair of 
inner rings, the load applied axially to the inner rings deforms 
elastically the outer rings and the rolling members. Consequently, the 
displacement amount is relatively larger with respect to the load. 
On the contrary, when a further load is applied in the state where the 
preload clearance has disappeared (to zero), the pair of the inner rings 
are also plastically deformed, so that the displacement amount is 
relatively smaller with respect to the load. In principle, the line 
depicting the relationship between the load and the displacement amount 
bends at the point where the preload clearance disappears, so that this 
point of bending indicates the preload clearance. 
However, it is impossible to detect the point of bending due to complicated 
states of deformation in the contact area between the rolling surfaces of 
rolling members, outer raceways and inner raceways. 
What is assured through experiments is the proportional relationship 
between the displacement amount and the preload clearance due to the fact 
that the point where the displacement amount is made smaller with respect 
to the load is changed due to the sizes of the preload clearances. 
Consequently, provided that the relationship between the displacement 
amount arid the preload clearance is previously obtained for the double 
row rolling bearing concerned, the preload clearance is obtained by 
measuring the displacement amount caused by the load. 
Now, an embodiment of the apparatus for measuring the preload clearance in 
the double row rolling bearing according to the present invention is 
explained referring to FIG. 1. 
The apparatus comprises a base plate 7 and a receiving block 8 fixed on the 
upper face of the base plate 7. The receiving block is made of such as a 
metal material which has a sufficient rigidity and is hard to be 
elastically deformed. 
Formed in the upper center portion of the receiving block 8 is a short, 
cylindrical protrusion 9 which is sized to be inserted in the first or 
lower inner ring 3a without play. 
Formed around the protrusion 9 on the end face of the receiving block 8 is 
an annular flat bearing surface 10 to which the outer end face (lower end 
face in FIG. 1) of the first or lower inner ring 3a is to be abutted. 
Formed in the central portion of the receiving block 8 is a through hole 11 
which is axially extended in the receiving block 8 and connected to a hole 
17 formed in the base plate 7. The opening of the through hole 11 is 
placed in alignment with the opening of the hole 17. 
Provided on the second or upper inner ring 3b is a retaining block 12 which 
is made of such as a metal material which is hard to be elastically 
deformed. 
Formed in the lower central portion of the retaining block 12 is a 
protrusion 13 which is sized to be inserted in the pair of inner rings 3a, 
3b. 
Formed around the protrusion 13 on the lower surface of the retaining block 
12 is an annular flat retaining face 14 to which the outer end face (upper 
end face in FIG. 1) of the second or upper inner ring 3b is abutted. 
The retaining block 12 has a sufficient weight to apply to the second inner 
ring 3b a light first toad downwards. 
Specifically, the first inner ring 3a is placed on the bearing face 10 of 
the receiving block 8 while the retaining block 12 is placed on the second 
inner ring 3b. In this state, the rolling faces of the rolling members 5, 
the outer raceways 2 and inner raceways are come into light contact with 
each other under substantially no preload. And, there is a clearance 6 
between the inner rings 3a and 3b at their inner end edges. The width size 
h of this clearance 6 is the preload clearance to be measured. 
Connected to the lower central portion of the protrusion 13 is the upper 
end portion of the transmission rod 15 which extends through the 
through-hole 11 in the central portion of the receiving block 8 and has a 
lower end which reaches the interior of the hole 17 formed in the base 
plate 7. 
Provided below the transmission rod 15 is a measuring device 16 to measure 
the vertical position of the lower end face 15a of the transmission rod 
15. The measuring device 16 has a probe 16a the upper end of which is 
abutted to the lower end face 15a of the transmission rod 15. 
Various conventional comparators can be used for the measuring device 16 
and many guide books are available on the comparators, Therefore, no 
explanation is made on the comparators in this specification. 
It is desirable to use the measuring device 16 from which the measured 
value is taken out as an electric signal in the case of automatic 
measurement. Such an electric signal is processed in a microcomputer and 
other processors. 
Disposed above the retaining block 12 is a pressing device (not shown) for 
applying a predetermined load to the upper face of the retaining block 12. 
For the pressing device, any hydraulic cylinder, air cylinder, feed screw 
mechanism etc. be used so long as a predetermined load can be applied to 
the upper face of the retaining block 12. 
In operation, the width size h of the clearance 6 between the inner end 
edge of the inner ring 3a and the inner end edge of the inner ring 3b is 
measured by the apparatus according to the present invention as follows; 
In the state where the first inner ring 3a is supported at its outer end 
face by the bearing face 10 of the receiving block 8, the retaining face 
14 of the retaining block 12 is abutted to the outer end face of the 
second inner ring 3b. 
As a result, the weight of the retaining block 12, that is a relatively 
smaller, constant first weight is applied to the outer end face of the 
second inner ring 3b. In this state, the level H.sub.1 of the lower end 
face 15a of the transmission rod 15 is detected by the measuring device 
16. The level H.sub.1 of the lower end face 15a corresponds to the 
position of the outer end face of the second inner ring 3b. 
The upper face of the retaining block 12 is pressed by the pressing device 
shown by an arrow in FIG. 1, so that a relatively larger, constant second 
load is applied to the outer end face of the second inner ring 3b. The 
second load is the sum of the force of the pressing device and the weight 
of the retaining block 12. In this state, the pair of inner rings 3a and 
3b are abutted to each other at their inner end edges, so that the 
clearance 6 disappears. 
Then, the level H.sub.2 of the lower end face 15a of the transmission rod 
15 is detected by the measuring device 16. The level H.sub.2 corresponds 
to the position of the outer end face of the second inner ring. 
The second load is desirably sufficiently large to reduce the preload 
clearance to zero and, in addition, to elastically deform the pair of 
inner rings 3a, 3b to a degree. This is to remove as much as possible the 
affects of complicated deformation caused at the contact areas between the 
rolling faces of the rolling members 5, outer raceways 2 and inner 
raceways 4. 
Then, based on the previously obtained relationship between the 
displacement amount and the preload clearance, the preload clearance h is 
obtained corresponding to the displacement amount of H.sub.2 -H.sub.1, 
that is the difference between the levels H.sub.1 and H.sub.2. 
The relationship between the displacement amount and the preload clearance 
is further explained as follows; 
A number of double row rolling bearings in the same model number as shown 
in FIG. 1 were prepared, and the displacement amount was measured for 
these bearings by changing the amount of the load axially applied to the 
outer end faces of the pair of inner rings 3a and 3b. The results are 
shown in FIG. 2, where the measurement results on six examples are 
illustrated. It is clear in FIG. 2 that the displacement amount is varied 
depending on the examples even with the same load applied. 
Then, the relationship between the actual preload clearance h and the 
displacement amount was measured when a predetermined load (700 kgf) was 
axially applied to the outer end faces of the bearings 3a, 3b. The results 
are shown on FIG. 3, where the measurement results are illustrated from 20 
kinds of examples. It is clear in FIG. 3 that there is a substantially 
proportional relationship between the displacement amount and the actual 
preload clearance h when a predetermined load is applied provided that the 
bearings are produced in the same model number and in the same dimensions 
on design. 
Therefore, once the relationship (straight line .alpha. in FIG. 3) between 
the displacement amount and the preload clearance h is previously obtained 
for the double row rolling bearings in the model number concerned, the 
preload clearance can be obtained from the displacement amount due to the 
load. 
Incidentally, the measurement of the preload clearance h can be precisely 
achieved by the methods previously known in the art e.g. referred to in 
(2) in the related art in this specification, 
In the case where the retaining face of the retaining block 12 is pressed 
against the outer face of the inner ring 3b through the elastic member 
such as a spring or a pressing device using a relatively low pressure 
fluid so as to provide the first load, the retaining block 12 and the 
receiving block 8 can be arranged in a lateral direction. 
In the present invention, the following effects are obtained; 
(1) The preload clearance is precisely measured before the actual preload 
is applied. 
(2) The automatic measurement is possible, and the whole number of the 
double row rolling bearings can be examined in situ at the bearing 
manufacturers. 
The creditability of such bearings and automobiles etc. with such bearings 
incorporated is increased. 
(3) The defective products can be instantly checked as they occur, and the 
defect condition, that is insufficient preload or excessive preload is 
simultaneously informed. 
Accordingly, such information is instantly fed back for eliminating such 
defective products. Thus, the number of defective products is minimized. 
(4) Measurement errors due to oil mist etc. deposited on the bearings are 
prevented.