22nd DANUBIA-ADRIA Symposium
                                on Experimental Methods in Solid Mechanics

                                           September 28 - October 1, 2005
                                         MONTICELLI TERME / PARMA - ITALY

                Ass. Prof., Ing. Vojtěch Dynybyl, Ph.D., Ing. Pavel Mossóczy, Ing. Zdeněk Češpíro

                         FME CTU in Prague, Technická 4, 166 07, Praha 6, Czech Republic

Introduction                                                Theoretical base
An experimental evaluation of two bevel gearboxes has       To compare a couple of similar gearboxes an exact
been arranged to compare them. Two parameters               methodology of measuring has been designed.
efficiency and lost power have been determined to           Conditions of experiments has been determined exactly
discover damage of gears. Parameters of gearboxes are       too.
power – 2,5 kW, speed – 1200min-1 and ratio – 3.            To compute lost power using SW, two values has been
                                                            measured: input torque Mk1 (pos. 4) and speed n1
Arrangement of measuring station                            (pos. 6). The output torque transducer has been
Fig. 1 shows block diagram of measuring station             disassembled. Computing equation of lost power is:
arrangement.                                                                     M k10 .n1
                                                                        PZ 0 =             [kW] .              (1.1)
                                                            Oil temperature, surface temperature and ambient
                                                            temperature have been measured to complete energy
                                                            information of gearboxes.
                                                            Since both gearboxes are arranged with tapered roller
                                                            bearings preload of them was desirable. It causes high
                                                            temperature and high lost power. This preload has to be
                                                            realized to fix forces of bevel gears.
                                                            Preload of mechanisms influenced the transfer of
                                                            power. Efficiency of this transfer shows quality of both
                                                            machining and assembling of gearboxes. It is an
                                                            important parameter of all gearboxes.
                                                            Supposing constant ratio i12, efficiency can be
                                                            calculated using SW formula:
                                                                                     M k2
                                                                               η=             ,                (5.3)
                                                                                    M k1 .i12
                                                            where Mk2 is measured output torque.
                                                            Data acquisition and data processing is done with
Fig. 1 Block diagram of measuring station arrangement       graphical programmable software LabVIEW.

   Basic measuring station consists of these                Results of measurement
equipments and devices:                                     Table 1 shows result of measurement of two gearboxes
    1. Measured gearbox,                                    A and B left and right rotation. Gearbox B is two times
    2. driving asynchronous electric motor,                 higher preload than A one.
    3. braking asynchronous electric motor,
    4. input torque transducer (HBM T20WN),
                                                                                     Mk1 [Nm] Pzo[W]
    5. output torque transducer (Vibrometer 100Nm)
    6. angle encoder of driving motor,                                A-Pz-L              0,68          85
    7. angle encoder of braking motor,                                A-Pz-R              0,71        89,5
    8. sensor of oil temperature and surface                          B-Pz-L              1,26         167
        temperature,                                                  B-Pz-R              1,36         170
    9. ambient temperature sensor,                                                    Table 1
    10. electrical device of out put torque transducer,     Fig. 2 shows results of measurement of gearbox A
    11. frequency inventor of braking motor,                rotating left. Different preload of bearings corresponds
    12. frequency inventor of driving motor,                to higher difference of power lost.
    13. PC
      Fig. 2 An example of lost power measuring                 Fig. 3 An example of efficiency measuring

An example of measuring (gearbox A rotation left) is      Comparing this value with difference of lost power we
documented in fig. 3. Table 2 includes results of         can see that the preload influence efficiency is less, if
measured efficiency [%] of gearboxes A and B,             load of gearbox is the highest.
rotation left and right. Increasing load of gearbox the
efficiency increases.                                     Conclusions
     Load         A_L       A_R       B_L     B_R             The goal of research was to determine cause of
          50%        87,2     86,6     76,7      82       pitting of gear. Solution was surprising. However the
                                                          efficiency of gearbox A was higher, the gear of that
          60%          89     88,2     81,5      86
                                                          one was damaged earlier than gear B. It has been
          70%        90,2     89,5     84,5    87,5       probably caused by lower quality of machining of gear
          80%          91     90,4     86,3    88,7       and axial vibrations of input shaft. Preload of them did
          90%        91,7     91,2     87,9    89,6       not exist and the clearance in tapered roller bearings
         100%        92,6     92,8     89,3    91,5       has been detected.
                         Table 2
                                                          [1] Dynybyl, V. - Chysky - Mossóczy, P. – Novák, J. –
                                                          Žák, P.: Experimental Analyses of Bevel Gearbox
                                                          25, kW. Research report. CTU in Prague, Prague 2004.
                                                          [2] Dynybyl, V.: Evaluation of Machine Drives Using
                                                          Simulation and Experiment. In: 19th Danubia-Adria
                                                          Symposiumon Experimental Methods in Solid
                                                          Mechanics-Abstracts. Warsaw : Warsaw University of
                                                          Technology, 2002, p. 30-31.
                                                          [3] Dynybyl, V. - Chyský, J.: Equipment for Testing
              Fig. 4 Summary of results                   and Measurement of Elektromechanical Rotary Drives.
                                                          In: SEKEL 2002. Trenčín : FM TnUAD, 2002, p. 48-
Summary of results is graphically realized in fig. 4.     50. ISBN 80-88914-73-6. (in Czech).
Percentage difference of efficiency of both gearboxes     This research has been supported by MSM grant
is only 3,3, when load is 100%.                           No. J04/98:21200008.

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