Gear Noise and Vibration Episode 1 Part 5 docx

[...]... at mesh facew=0 10 5; bpitch=0. 017 7; % specify tooth geometry 6mm mod ++++ misalig=40e-6;bprlf=25e-6; % relief at 0 .5 base pitch from pitch point strelief = 0.2; % start linear relief as fraction of bp from pitch pt slicew=facew/ 21 ;tanbhelx=0 .18 ;tthst = 1, 4e 10 ; % standard value relst=strelief*bpitch;tthdamp = Ie5; % eff.value at 10 000 rad/s Q = 14 ++ ss = (1: 21 );hor = ones( 1, 21) ; % 21 slices across... with a coefficient tthdamp which is derived by taking the standard tooth stiflhess coefficient 1. 4 *10 10 and dividing it by a Q of 14 to give 10 9 N/m/m Then since peak velocity is ox if peak displacement is x, assuming a resonant frequency in contact of 16 00 Hz or 10 ,000 rad/s, we get a damping coefficient of 10 9 N/m/m divided by 10 ,000 to give 10 5 N per unit velocity per unit facewidth (N s/m2) This damping... design References 1 2 Lim, T.C., and Singh, R., 'A review of gear housing dynamics and acoustics literature.' NASA Contractor Report 18 51 4 8 Oct 19 89 Fahy, F.J Sound and structural vibration Academic Press, London, 19 93 Measurements 6 .1 What to measure As it is gearbox noise that is the problem, the obvious thing to measure is noise, with a microphone placed in typical listening positions around the installation... ; qpr =1. 5e2 ; qwr = 3e3 ; % eff damping coeffts tr=3000; % fixed tooth load for ddd = 1: 40; % start of frequency loop freq = 50 * ddd ; kk = round(20000/freq); % steps for 1 tooth mesh timint = 5e -5 ; % time for single step 1/ 20000 sec predefl = tr * (1 /Kpr + 1 /sp +1 /sw + 1 /Kwr); % elastic defi.of shafts % and torsions under steady torque referred to contact, then zero of % input torsion is predefl... us the original vibration generation information and the accelerometers give the casing and system response information 6.2 Practical measurements As far as noise measurements and deductions are concerned there are few restrictions on measurements Measurement of sound pressure levels is easy since a basic (digital) noise meter with analog output jack [1] can cost less than 10 0 ( $ 15 0) and the output... stiffness and the effective masses of the gears Chapter 5 72 20 10 10 00 2000 frequency of excitation Fig 5. 5 Prediction of variation of maximum contact force with tooth frequency In the example given, the highest natural frequency (when in full contact) is of the order of 16 00Hz so with a periodic time of 600us, a time interval of 50 u,s was taken A test run with half the time interval (25us) quickly... up combined noise from all the panels of a gearcase and the relatively low speed of sound in air (300 m/s compared with 50 00 m/s in steel) means that at a typical tooth meshing frequency of 600 Hz the wavelength is 0 .5 m Two panels vibrating in phase 0. 25 m apart will produce sound waves exactly 18 0° out of phase The interference between the waves will have a major effect on the sound and small variations... investigating noise source problems Using accelerometers to roam around the casing or installation allows us to deduce where the large noise- producing vibrations are occurring Measurement of transmission error at the gear mesh, discussed in Chapter 7, is essential and is powerful and informative, but more difficult and requires more expensive equipment It gives us the information about the excitation from the gears... short shafts and the bearing stiffnesses are susceptible to small changes in alignments and casing design It is possible to measure stiffnesses in situ but bearing lateral stiffnesses and their restraining stiffness against misalignment vary with 74 Chapter 5 speed, load, and frequency for plain bearings and with load for rolling bearings We conventionally make the assumption that the gearcase is rigid... assumption Some gearcases may deflect rather easily, reducing effective stiffness at low frequency When above a natural frequency, the gearcase bearing housings may respond 18 0° out of phase This gives motion of the housing opposing the bearing and shaft deflections and so there appears to be an increase in the support stiffness and natural frequencies are higher than expected (iii) Gear support damping . pt slicew=facew/ 21 ;tanbhelx=0 .18 ;tthst = 1, 4e 10 ; % standard value relst=strelief*bpitch;tthdamp = Ie5; % eff.value at 10 000 rad/s Q = 14 ++ ss = (1: 21 );hor = ones( 1, 21) ; % 21 . 30). 20 10 0 10 20 time in milliseconds Fig 5. 3 Prediction of contact force variation with time with helical gear. Prediction of Dynamic Effects 69 -13 0 - 15 0 ex c " ;5, -17 0 10 time . pt slicew=facew/ 21 ;tanbhelx=0 .18 ;tthst = 1. 4el 0 ; % standard value Prediction of Dynamic Effects 67 relst=strelief*bpitch;tthdamp = Ie5; % eff.value at 10 000 rad/s Q = 14 +++ ss = (1: 21