Gear­box mea­sure­ments

Prob­lem: Gear noise, trans­mis­sion error (TE)
Goal: Reli­able gear­box design, noise reduc­tion

Dis­turb­ing trans­mis­sion noise, vibra­tion and rough­ness (NVH, Noise Vibra­tion Harsh­ness) seri­ous­ly reduce dri­ving com­fort — espe­cial­ly in vehi­cles with low-noise elec­tric motors. Noise can be reduced with a reli­able trans­mis­sion design. There­fore, it is nec­es­sary to mea­sure and ana­lyze the trans­mis­sion error.

Gear noise
Gear whine is main­ly caused by the tooth pro­file and tooth vibra­tions. In the spec­trum of the trans­mis­sion error and the struc­ture or air­borne noise, the tooth mesh fre­quen­cies with their har­mon­ics and mod­u­la­tion side­bands (caused by the rota­tion­al har­mon­ics; e.g. runout) show up.
Gear whine can occur at high and low load, gear­box rat­tle only at very low or no load (e.g. idling in an com­bus­tion engine). Then, the speed fluc­tu­a­tion com­ing from the engine (non-con­tin­u­ous com­bus­tion) caus­es the unloaded tooth flanks of the gears to lift off. The back­lash is passed through with every accel­er­a­tion and decel­er­a­tion of the dri­ve shaft (sev­er­al times per rev­o­lu­tion), where­by the teeth of the two gears vio­lent­ly strike against each oth­er.
Oth­er caus­es of gear noise can be improp­er gear oil or air bub­bles in the oil.

Trans­mis­sion Error (TE)
The main rea­son for gear noise are trans­mis­sion errors (TE) caused by sta­t­ic and elas­tic defor­ma­tion under load, unin­ten­tion­al man­u­fac­tur­ing devi­a­tions and dynam­ic effects. The trans­mis­sion error is the dif­fer­ence between the actu­al posi­tion of the out­put gear and the posi­tion it would occu­py if the gear set trans­mit­ted the rotary motion of the input gear per­fect­ly with­out error.
In addi­tion to gear noise, the trans­mis­sion error can cause wear, low­er effi­cien­cy in the dri­ve train or imme­di­ate mal­func­tions (more about wind tur­bine gear­box, rolling ele­ment gears).

Gear­box mea­sure­ments
To deter­mine the trans­mis­sion error, the rota­tion­al speeds and angu­lar posi­tions are mea­sured using high-res­o­lu­tion rotary encoders on the input and out­put shafts. The trans­mis­sion error is cal­cu­lat­ed from the mea­sured data. The eval­u­a­tion is done in the time and order domain. At the same time, struc­ture-borne noise sig­nals are record­ed with an accelerom­e­ter. The com­mon time base of all mea­sur­ing chan­nels enables a cor­re­la­tion between trans­mis­sion error and sound sig­nals.

ROTEC ENGI­NEER­ING 
You need sup­port with vibra­tion analy­sis on engines, gear­box­es, and dri­ve trains? Our engi­neers con­sult you with exten­sive know-how in the areas of

• tim­ing gear val­i­da­tion
• valve train opti­miza­tion
• clutch design
• trans­mis­sion errors (TE)
• oil sup­ply opti­miza­tion
• pow­er­train mea­sure­ment and opti­miza­tion
• cur­rent and volt­age analy­sis
• appli­ca­tion of mea­sure­ment tech­nol­o­gy.