Double-Row Thrust Needle Roller Bearings for Automotive Air

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Double-Row Thrust Needle Roller Bearings for Automotive Air Powered By Docstoc
					                                       NTN TECHNICAL REVIEW No.73            2005

                                                    New Product


           Double-Row Thrust Needle Roller Bearings
  for Automotive Air Conditioners and Automatic Transmissions



                                                                                         Kosuke OBAYASHI




      In order to meet the customer's need for longer service life, lower torque and lower noise bearings,
    NTN has developed double-row thrust needle roller bearings.
       By using two rows of needle rollers in each retainer pocket and by optimizing the roller shape,
    NTN has successfully minimized roller slippage, achieved extended service lives and reduced torque
    and noise in thrust bearings.




 1 Introduction                                                    2. Features of double-row thrust needle
                                                                      roller bearings (for automotive air-
   In recent automotive bearing applications, smaller
                                                                      conditioner compressors)
amounts of lower viscosity lubricants are being used
to achieve better fuel consumption. As a result, the                 The thrust bearings for automotive air-conditioner
operating conditions for bearings have become                     compressors are run with limited amounts of low-
increasingly severe.                                              viscosity lubricant in order to improve the capability of
   In this context, a unique problem for thrust needle            the compressors. Lower viscosity lubrication will be
roller bearings have decreased bearing life because of            further needed to help realize better automobile fuel
roller slipping. Bearings with longer lifespans are               efficiency. Reduced bearing life poses a problem to be
needed.                                                           solved.
   We recently developed "double-row thrust needle                   In addition, as CFC refrigerant is replaced with CO2
roller bearings" to cope with this market need. These             refrigerant to help preserve the global environment, a
bearings have a double-row roller arrangement to                  higher refrigerant compression ratio is increasingly
inhibit the slipping of needle rollers and to achieve             needed, which in turn leads to decreased bearing life.
longer life through prevention of surface-start failure.             Our newly developed double-row thrust needle
They also have lower torque and, through roller shape             roller bearing (Photo 1) maintains load carrying
optimization, lower noise level.                                  capacity and suppresses roller slipping. The double-
   For automotive air-conditioner compressors, we                 row roller arrangement prevents surface-start failures
have developed a resin cage to achieve lighter weight             that result from disrupted oil film on bearing rolling
and lower noise. For automatic transmissions, we                  surfaces. Our new bearing adopts optimal roller
designed a new sheet steel cage with inner and outer              geometry (optimal end face shape, roller circularity
circumferences that are secured by a full enclosure               and crowning) and a lightweight resin cage (of high
technique to prevent cage loosening and to enhance                wear resistant material) to achieve longer bearing life,
cage mechanical strength. These cage types are                    lower torque and lower noise.
described below.

Automotive Sales Headquarters Needle Roller Bearings Engineering Dept.


                                                           -48-
                                                                                   Double-Row Thrust Needle Roller Bearings




   Photo 1 Double-row thrust needle roller bearings                                    Photo 2 Current bearings
              for car air conditioners




[Comparison with single-row bearing in terms                      2.1.1 Bearing specification
of performance]                                                     The bearings used for the performance evaluation
  (NTN's test results for automotive air-conditioner              have 60 mm inside diameters, 85 mm outside
  compressors)                                                    diameters and are 3 mm wide (roller diameter).
  1 Life (surface-starting failure) : 12 times as long              Table 1 lists the data for both our newly developed
  2 Rotation torque                 : 50% reduction               bearing and the standard bearing.
  3 Noise                           : 8 dBA lower
                                                                        Table 1 Comparison of bearing specifications
                                                                                       Newly developed bearing        Standard bearing
2.1 Performance evaluation                                                                (double-row type)           (single-row type)
  To evaluate performance of thrust needle roller                 Bearing size               60ID         85OD   3W (roller diameter)
bearings for automotive air-conditioner compressors,
                                                                  Cage type                  Resin cage            W-type sheet steel cage
we compared our newly developed bearing with a
                                                                  Number of rollers        96 (48     2 rows)                48
standard bearing that has a W-type sheet steel cage
                                                                  Roller length (mm)                3.8                      7.8
and a single-row roller arrangement (Photo 2). We
subjected both bearing types to rotation torque and
running noise measurements after a bearing life test.             2.1.2 Bearing life test
This section summarizes the performance evaluation                   For the bearing life test, we used the NTN vertical
tests of both bearing types.                                      thrust bearing test rig illustrated in Fig. 1 and the NTN
                                                                  horizontal thrust bearing test rig shown in Fig. 2.




                         Load
                                    Bearing being tested                      Bearing being tested




                                                                     Load




     Fig 1 NTN vertical type thrust bearing test rig                   Fig 2 NTN horizontal type thrust bearing test rig


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 NTN TECHNICAL REVIEW No.73                   2005


(1) Test conditions




                                                                              Accumulated failure probability, %
  Two sets of bearing life test conditions are given in                                                            95
                                                                                                                   90         Standard bearing
Tables 2 and 3.                                                                                                    80         Newly developed
                                                                                                                   70         bearing
                                                                                                                   60
                                                                                                                   50
                                                                                                                   40
                 Table 2 Life test condition 1                                                                     30
Test rig                    NTN vertical thrust load test rig                                                      20

Axial load                  P C = 0.4 with standard bearing                                                        10

Bearing speed               5000 min-1                                                                              5

Misalignment on race        2/1000
                                                                                                                        5 7     1     2   3   5 7 1          2   3   5 7 1         2       3   5   7
Lubrication                 Turbine #32, circulating lubrication                                                                101               102                    103
                                                                                                                                                    Life, h
Number of samples           n=8, each bearing type
 P C : load/basic dynamic rated load                                        Fig 3 Result of life test condition 1 with misalignment
                                                                                           for car air conditioners

                 Table 3 Life test condition 2
Test rig                 NTN horizontal type thrust load test rig
Axial load               P C = 0.4 with standard bearing                    Accumulated failure probability, %     95
                                                                                                                   90         Standard bearing
Bearing speed            5000 min-1                                                                                80         Newly developed
                                                                                                                   70         bearing
                                                                                                                   60
                         PAG (3%) + clean kerosene (97%),                                                          50
Lubrication              circulating lubrication                                                                   40
                                                                                                                   30
Number of samples        n=8, each bearing type                                                                    20

                                                                                                                   10

                                                                                                                    5


(2) Test results                                                                                                        1        2    3   5 7     1      2       3   5   7   1         2       3   5
                                                                                                                        101                       102                        103
   The life test result of test condition set 1 is                                                                                                  Life, h
summarized in Fig. 3, and that from test condition set
2 is given in Fig. 4.                                                      Fig 4 Result of life test condition 2 with lean lubrication
                                                                                            for car air conditioners
   Compared with the standard bearing, our newly
developed bearing exhibited a life more than 12 times
as long in terms of L10 under both test condition sets 1
and 2.                                                                                                                                        Rotation


2.1.3 Rotation torque measurement
   For measuring the rotation torque of the bearings
being tested, the NTN vertical thrust bearing rotation
torque test rig was used.                                                                                                                                                Bearing being
   The test rig is illustrated in Fig. 5                                                                                                                                    tested


(1) Measuring conditions
   The rotation torque measuring conditions are listed                                                                                                                    Rotation torque
                                                                                                                                                                         detection load cell
in Table 4.


   Table 4 Measurement condition of rotation torque
Test rig               NTN vertical-type thrust torque test rig                                                                                  Load
Axial load             P C = 0.1, 0.15, 0.2 with standard bearing          Fig 5 NTN vertical type thrust bearing rotation torque
Bearing speed          1000 min-1                                                                 test rig
Lubrication            Category 1 spindle oil, overall coating
Measuring duration 60 sec.
Number of samples n=10, each bearing type




                                                                    -50-
                                                                                                                                  Double-Row Thrust Needle Roller Bearings


(2) Measurement results                                                                              2.1.4 Sound measurement
   The measurement results of rotation torque are                                                     For sound measurement, the NTN sound level
plotted in Fig. 6.                                                                                   measuring system was used.
   These results verify that the newly developed
bearing has achieved 47 to 51% torque reduction                                                      (1) Measuring conditions
compared with the standard bearing.                                                                    The sound level measurement conditions are
   This torque reduction was achieved by both the                                                    summarized in Table 5.
double-row roller arrangement, which reduced spin
slippage, and the cage resin material.                                                               (2) Measurement results
   The measured rotation torques were dependent on                                                      The sound level measurement results are given in
loading, but rotation speed caused virtually no                                                      Fig. 7.
variation.                                                                                              Compared with the standard bearing, the newly
                                                                                                     developed bearing achieved a sound level reduction
                                                                                                     of approximately 8 dBA at 1800 min-1, and
                                                                                                     approximately 11 dBA at 3600 min-1.
                                Standard bearing: W-type cage + single-row rollers                      The contributing factors for these reductions are the
                                Newly developed bearing: resin cage + double-row rollers
                        80
                                                                                                     resin-made cage and the optimized roller shape.
 Rotation torque N cm




                        60
                                                                                                                        Table 5 Measurement condition of sound level
                        40                                                                           Test rig                                    NTN sound level measuring system
                                                                                                     Axial load                                  100N
                        20                                                                           Measurement distance                        45˚ angle, 100
                                                                                                     Bearing speed                               1800 min-1      3600 min-1
                         0                                                                                                                       Compressor oil,
                         0.05            0.10           0.15             0.20          0.25
                                                                                                     Lubrication                                 droplet lubrication before running
                                                        P/C                                          Measuring duration                          50 sec.
                                                                                                     Number of samples                           n=10, each bearing type
                        Fig 6 Measurement result of rotation torque




                                                                                                                               Standard bearing: W-type cage + single-row rollers
                                                                                                                               Newly developed bearing: resin cage + double-row rollers
                                                                                                                        90



                                                                                                                        85
                                                                                                      Sound level dBA




                                                                                                                        80



                                                                                                                        75


                                                                                                                        70


                                                                                                                        65
                                                                                                                                  1800 min-1                          3600 min-1

                                                                                                                             Fig 7 Measurement result of sound level




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 NTN TECHNICAL REVIEW No.73          2005


                                                                  [Comparison with single-row bearing]
 3. Feature of double-row thrust needle                             (NTN's test results assuming application in
    roller bearings                                                 automatic transmissions)
    (for automatic transmissions)                                   1 Life (surface-starting failure)
   Featuring a lower profile in assembled units and a                                         : Three times as long
greater load carrying capacity, thrust needle roller                2 Rotation torque         : 40% decrease
bearings are often used for automatic transmissions in              3 Cage strength           : 1.6 times as strong
automobiles. However, the use of lower viscosity                    4 Sound level             : Decrease of 3 dB
automatic transmission oils is increasing to alleviate
shift shock and improve fuel efficiently. For this                3.1 Performance evaluation
reason, the life of bearings used in this application                Under conditions that simulated automatic
may be shortened.                                                 transmissions, the newly developed double-row thrust
   Our newly developed double-row thrust needle                   needle roller bearing was compared with a standard
roller bearing (Photo 3) for automatic transmissions              bearing that has a W-type sheet steel cage and
has a double-row roller arrangement to inhibit roller             single-row rollers. Performance evaluations were
slipping while maintaining the necessary load carrying            conducted through FEM analysis, bearing life tests,
capacity. The newly developed bearing features                    eccentric rotation tests, rotation torque measurements
optimized roller geometry (with optimized roller end              and sound level measurements. The results are
face shape, roller roundness and crowning shape) to               summarized below.
achieve a longer bearing life, lower rotation torque and
quieter operation.                                                3.1.1 Bearing specifications
   In addition, because thrust bearings are used in                 The bearings used for performance specification
eccentric rotation conditions in automatic                        were 60 mm inside diameter, 85 mm outside diameter
transmissions, cages can be pinched and damaged by                and are 3 mm wide (roller diameter).
bearing rings and the cage halves themselves can                    The bearing specifications for the newly developed
split apart. Therefore, higher cage strength is needed.           bearing and the standard bearing are summarized in
To address this problem, we have invented and                     Table 6.
developed a new cage uniquely shaped with full
enclosure of inner and outer ring circumferences,
                                                                        Table 6 Comparison of bearing specifications
improving cage mechanical strength. This
                                                                                       Newly developed bearing         Standard bearing
arrangement prevents separation of cage halves or                                         (double-row type)            (single-row type)
displacement between the halves and allows                        Bearing size                 60ID        85OD   3W (roller diameter)
integration of the cage with the bearing ring to form a
                                                                  Cage type            Sheet steel cage of new shape W-type sheet steel cage
unified structure.
                                                                  Number of rollers         96 (48     2 rows)                48
                                                                  Roller length (mm)                 3.8                      7.8




                                                                                          Double-row rollers




                                                                                  Full circumference enclosure



                     Photo 3 Double-row thrust needle roller bearings for automatic transmissions


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                                                                                                                                 Double-Row Thrust Needle Roller Bearings


3.1.2 FEM analysis                                                               The maximum principle stress on the standard
  The results of FEM analysis for the newly                                    bearing was compared with that on the newly
developed bearing and the standard bearing are                                 developed bearing. As a result, the stress on the
summarized below.                                                              newly developed bearing was 0.62 relative to that of
(1) Analysis conditions                                                        the standard bearing rating of 1. The cage of the
  The analysis conditions are shown in Fig. 8.                                 newly developed bearing has increased strength.
(2) Analysis results                                                              Note: The weight of the newly developed bearing is
  The analysis results are given in Fig. 9.                                             5% lighter than the standard bearing.




                                                                                                                                               Fully constrained
           Load (50% load on the outer                                                                                                         (inner circumference surface)
           circumference surface and
           50% load on the bars and
           pockets)


                                                           Fig 8 Analytical condition

                                 Standard bearing                                                                                     Newly developed bearing




                                                    Location where maximum principle load occurs

                                                             Fig 9 Analytical result



3.1.3 Bearing life test
                                                                                 Accumulated failure probability, %




   For the bearing life test, the NTN vertical thrust test                                                            95
                                                                                                                      90       Standard bearing
rig illustrated in Fig. 1 was used.                                                                                   80       Newly developed
                                                                                                                      70       bearing
(1) Test conditions                                                                                                   60
                                                                                                                      50
  The test conditions are summarized in Table 7.                                                                      40
                                                                                                                      30
(2) Test results                                                                                                      20
  The results of bearing life tests are summarized in
                                                                                                                      10
Fig. 10.
                                                                                                                       5
  In L10 terms, the life of the newly developed bearing
was three times as long as that of the standard                                                                            5      7     1         2     3       5   7    1     2
bearing.                                                                                                                                101                             102
                                                                                                                                                      Life, h

                   Table 7 Life test condition                                   Fig 10 Result of life test for automatic transmissions
Test rig                        NTN vertical type thrust test rig
Axial load                      P   C=0.4 on standard bearing
Bearing speed                   8000 min-1
                                ATF, circulating lubrication
Lubrication
                                Oil temperature, 100˚C
Number of samples tested        n=8 each



                                                                        -53-
 NTN TECHNICAL REVIEW No.73                                     2005


3.1.4 Eccentric rotation test                                                               For the eccentric rotation test, the NTN eccentric
   If the inner ring and outer ring rotate on an offset                                  rotation vertical thrust test rig was used.
rotation center and the eccentricity is greater than the                                    The test rig used is illustrated in Fig. 11.
clearance of the bore, then the cage will be pinched                                     (1) Test conditions
between the races (inner ring and outer ring).                                             The test conditions for the eccentric rotation test are
Consequently, the cage is subjected to a compression                                     summarized in Table 8.
force in the radial direction and a shear force in the                                   (2) Test results
rotation direction resulting from the difference between                                    The results of the eccentric rotation test are given in
the rotation speed of the inner race and that of the                                     Table 9.
outer race, leading to eventual fracture.                                                   A ring-shaped fracture occurred on the bore side of
   The situation above exists particularly in the torque                                 the cage bar of the conventional bearing. In contrast,
converters of automatic transmissions. To address                                        no fracture was found in the newly developed cage.
this problem, we checked the mechanical strength of                                         Compared with the conventional cage, the new
the new cage shape.                                                                      cage, with a unique form created by full enclosure of
                                                                                         inner and outer circumferences, exhibited improved
                                                                                         strength that matches the results of FEM analysis.
                                              Load
                                                                       Bearing
                                                                        tested           3.1.5 Rotation torque measurement
                                                                                           The rotation torque of the bearings was measured
                                                                                         with the NTN vertical thrust torque test rig illustrated in
                                                                                         Fig. 5.
                                                                                         (1) Measuring conditions
                                                                                           The rotation torque measuring conditions are
                                                                                         summarized in Table 10.
                                                                                         (2) Measurement results
                                                                                             The rotation torque measurement results are
                                                                                         illustrated in Fig. 12.




                  Fig 11 NTN vertical type thrust bearing test rig                                       Table 10 Measurement condition of rotation torque
                            for eccentricity rotation
                                                                                          Test rig                                 NTN vertical thrust torque test rig
                                                                                          Axial load                               P C = 0.1, 0.15, 0.2 with standard bearing
                    Table 8 Eccentricity rotation test condition                          Bearing speed                            1000 min-1
                                              NTN eccentric rotation vertical             Lubrication                              Category 1 spindle oil, overall coating
Test rig
                                              thrust test rig
                                                                                          Measuring duration 60 sec.
Axial load                                    P   C=0.3 on standard bearing
                                                                                          Number of samples n=10, each bearing type
Bearing speed                                 3000 min-1
Eccentricity (rotation axis)                  0.5mm

Lubrication                                   ATF, circulating lubrication
                                                                                                                         Standard bearing: W-type cage + single-row rollers
                                              Oil temperature, 100˚C
                                                                                                                         Newly developed bearing: resin cage + double-row rollers
Number of samples tested                      n=3 each                                                           80
                                                                                          Rotation torque N cm




                    Table 9 Result of eccentricity rotation test                                                 60

                  Bearing
                              Running time, h                    Remarks
                    No.                                                                                          40
                                                        Ring-shaped fracture
Standard




                    1               53.4
 bearing




                                                      on the cage bar bore side
                    2               51.5                                                                         20

                    3               60.5
Newly developed




                    1       Suspended at 265.0 hrs.             No failure                                        0
  bearing




                                                                                                                  0.05           0.10            0.15            0.20           0.25
                    2       Suspended at 265.0 hrs.                                                                                              P/C
                    3       Suspended at 265.0 hrs.                                                              Fig 12 Measurement result of rotation torque


                                                                                  -54-
                                                                                                            Double-Row Thrust Needle Roller Bearings


   As a result of the measurement, we found that
compared with the standard bearing, the rotational                                                      Standard bearing: W-type cage + single-row rollers
                                                                                                        Newly developed bearing: resin cage + double-row rollers
torque of the newly developed bearing is 38-43%                                                  90
lower.
   The primary factor contributing to the torque                                                 85




                                                                               Sound level dBA
reduction is the reduction of spin slipping due to the
double-row roller design.                                                                        80

   When comparing the newly developed cage with the
conventional cage, other possible contributing factors                                           75

are a smaller contact area between the cage and shaft
and a smaller contact width between the cage and                                                 70

rollers.
                                                                                                 65
   We also learned that the rotation torque is                                                             1800 min-1                        3600 min-1
dependent on the load applied to the bearing tested
and is least affected by the bearing running speed.                                                   Fig 13 Measurement result of sound level


3.1.6 Sound level measurement
  For sound level measurement, the NTN sound level
test system was used.                                                            4. Conclusion
(1) Measuring conditions                                                         This report described our newly developed double-
  The sound level measuring conditions are                                    row thrust needle roller bearings.
summarized in Table 11.                                                          In this report, the scope of application for our newly
(2) Measurement results                                                       developed bearings were limited to automobile air-
    The sound level measurement results obtained are                          conditioner compressors and automatic transmissions
illustrated in Fig. 13.                                                       and we evaluated them only for these applications.
    At 1800 min-1, the sound level of the newly                               However, these new bearings are also capable of
developed bearing was approximately 3 dBA lower,                              applications in other types of machinery.
and at 3600 min-1, approximately 2 dBA lower.                                    The operating conditions for bearings will become
    The factor contributing to this sound suppression is                      increasingly severe. Therefore, we will remain
optimization of the roller geometry.                                          committed to the development and marketing of novel
                                                                              bearing products that only NTN can offer, always
       Table 11 Measurement condition of sound level                          aiming to increase customer satisfaction and satisfy
                                                                              market needs.
 Test rig                       NTN sound level measuring system
 Axial load                     100N
 Measurement distance           45˚ angle, 100
 Bearing speed                  1800 min-1   3600 min-1
                                ATF,
 Lubrication                    droplet lubrication before operation
 Measuring duration             50 sec.
 Number of samples              n=10, each bearing type



Photos of author




  Kosuke OBAYASHI
Automotive Sales Headquraters
    Needle Roller Bearings
      Engineering Dept.



                                                                       -55-

				
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