Tribo-dynamic analysis of hypoid gears in automotive differentials

Torsional vibrations in differentials of Rear Wheel Drive vehicles are of major importance for the automotive industry. Hypoid transmissions, forming the motion transfer mechanism from the driveshaft to the wheels, suffer from severe vibration issues. The latter are attributed to improper mesh between the mating gear flanks due to misalignments, variation of contact load and shifting of the effective mesh position. For certain operating conditions, the gear pair exhibits high amplitude motions accompanied with separation of the mating surfaces. Ultimately, single or even double-sided vibro-impact phenomena evolve, which have been related to noise generation. This thesis attempts to address these issues by effectively analysing the dynamic behaviour of a hypoid gear pair under torsional motion. The case study considered is focused on a commercial light truck. The major difference of the employed mathematical model to prior formulations is the usage of an alternative expression for the dynamic transmission error so that the variation of contact radii and transmission error can be accounted for. This approach combined to a correlation of the resistive torque in terms of the angular velocity of the differential enables the achievement of steady state, stable periodic solutions. The dynamic complexity of systems with gears necessitates the identification of the various response regimes. A solution continuation method (software AUTO) is employed to determine the stable/unstable branches over the operating range of the differential. The ensuing parametric studies convey the importance of the main system parameters on the dynamic behaviour of the transmission yielding crucial design guidelines. A tribo-dynamic investigation aims at expanding the dynamic model from pure dry conditions to a more integrated elastohydrodynamic (EHL) approach. Analytical and extrapolated solutions are applied for the derivation of the film thickness magnitude based on the kinematic and loading characteristics of the dynamic model. The temperature rise is governed mainly by conduction due to the thin lubricant films. The generated friction is also computed as a function of the viscous shear and asperity interactions. The effective lubricant viscosity is greatly affected by the pressure increase due to the resonant behaviour of the contact load. The final part of this work is involved with a feasibility study concerning the application of Nonlinear Energy Sinks (NES) as vibration absorbers, exploiting their ability for broadband frequency interaction. Response regimes associated with effective energy absorption are identified and encouraging results are obtained, showing the potential of the method

An alternative formulation of the dynamic transmission error to study the oscillations of automotive hypoid gears

A new modelling approach on the torsional dynamics of hypoid gear pairs is presented in this work. The current formulation is characterised by an alternative expression of the Dynamic Transmission Error (DTE), accounting for the variation of the effective mesh position. Speed dependent resistive torque is introduced on the gear wheel, enabling the system to reach dynamic equilibrium based on realistic vehicle operating conditions. The above are supplementing past research studies, where simplifications were introduced in the calculation of DTE, while the operating angular velocity was defined a priori. The analysis is accompanied by numerical results, indicating the rich dynamic behavior captured by the new formulation. The dynamic complexity of the system necessitates the identification of the various response regimes. A solution continuation method (software AUTO) is employed to follow the stable/unstable periodic response branches over the operating range of the differential under examination

On the dynamics of lubricated hypoid gears

The torsional dynamics of a vehicle differential hypoid gear pair is investigated. The model comprises applied torque, representing transmitted engine power, including engine order vibration. A number of gear teeth pairs transmit the applied torque through their lubricated conjunctions. Tooth contact analysis (TCA) is used to obtain the appropriate geometrical, kinematic and meshing parameters. These enable the evaluation of contact loads, film thickness and friction for conjugate teeth pairs, which are subject to mixed thermo-elastohydrodynamic regime of lubrication. It is shown that the lubricant undergoes non-Newtonian shear in line with the Eyring regime of traction. The inclusion of combined thermal non-Newtonian shear and boundary interactions has not hitherto been reported for the tribo-dynamics of hypoid gear pairs. When rate of change of gear teeth contact radii is included in the analysis more complex system dynamics (loss of teeth contact) result, particularly at higher speeds. The stated features constitute the main contributions of the current work, which have not hitherto been reported in literature. It is also shown that teeth contact separation ensues when resonant conditions are noted. This is regarded as the main root cause of a noise and vibration phenomenon, known as axle whine

Vaccine effectiveness of live (LAIV) and inactivated vaccines (TIV) against laboratory-confirmed influenza of all subtypes, stratified by age groups; Multivariable logistic regression, Virological Surveillance, Saxony-Anhalt, Germany 2012/13 (n = 798).

<p>^a. VE (vaccine effectiveness) adjusted for month of illness, sex;</p><p>^b. VE adjusted for month of illness, sex, age group</p><p>Vaccine effectiveness of live (LAIV) and inactivated vaccines (TIV) against laboratory-confirmed influenza of all subtypes, stratified by age groups; Multivariable logistic regression, Virological Surveillance, Saxony-Anhalt, Germany 2012/13 (n = 798).</p

Laboratory results from specimens of patients swabbed during the study period from week 40/2012 to 19/2013, Virological Surveillance, Saxony-Anhalt.

<p>*RSV (respiratory syncytial virus), HMPV (human metapneumovirus)</p><p>Laboratory results from specimens of patients swabbed during the study period from week 40/2012 to 19/2013, Virological Surveillance, Saxony-Anhalt.</p

Vaccine effectiveness of live (LAIV) and inactivated vaccines (TIV) against laboratory-confirmed influenza A(H3N2), A(H1N1)pdm09 and B; Multivariable logistic regression, Virological Surveillance, Saxony-Anhalt, Germany 2012/13, age group 2–17 years, (n = 798).

<p>^a. VE (vaccine effectiveness) adjusted for month of illness, sex, age group</p><p>Vaccine effectiveness of live (LAIV) and inactivated vaccines (TIV) against laboratory-confirmed influenza A(H3N2), A(H1N1)pdm09 and B; Multivariable logistic regression, Virological Surveillance, Saxony-Anhalt, Germany 2012/13, age group 2–17 years, (n = 798).</p

Outbreak of Uncommon O4 Non-Agglutinating <i>Salmonella</i> Typhimurium Linked to Minced Pork, Saxony-Anhalt, Germany, January to April 2013

<div><p>Introduction</p><p>In January 2013, the National Reference Centre for <i>Salmonella</i> (NRC) detected a salmonellosis cluster in Saxony-Anhalt, Germany, caused by uncommon O4 non-agglutinating, monophasic <i>Salmonella</i> (<i>S</i>.) Typhimurium DT193. Circulating predominant monophasic <i>S</i>. Typhimurium DT193 clones typically display resistance phenotype ASSuT. We investigated common exposures to control the outbreak, and conducted microbiological investigations to assess the strains’ phenotype.</p><p>Methods</p><p>We conducted a case-control study defining cases as persons living or working in Saxony-Anhalt diagnosed with the O4 non-agglutinating strain between January and March 2013. We selected two controls contemporarily reported with norovirus infection, frequency-matched on residence and age group, per case. We interviewed regarding food consumption, especially pork and its place of purchase. We calculated odds ratios (ORs) with 95% confidence intervals (95% CI) using logistic regression. The NRC investigated human and food isolates by PCR, SDS-PAGE, MLST, PFGE, MLVA and susceptibility testing.</p><p>Results</p><p>Altogether, 68 O4 non-agglutinating human isolates were confirmed between January and April 2013. Of those, 61 were assigned to the outbreak (median age 57 years, 44% female); 83% cases ≥ 60 years were hospitalized. Eating raw minced pork from butcheries within 3 days was associated with disease (31 cases, 28 controls; OR adjusted for sex: 3.6; 95% CI: 1.0-13). Phage type DT193 and MLST ST34 were assigned, and isolates’ lipopolysaccharide (LPS) matched control strains. Isolates linked to Saxony-Anhalt exhibited PFGE type 5. ASSuT- and ACSSuT phenotype proportions were 34 and 39% respectively; 54% were resistant to chloramphenicol. Three pork isolates matched the outbreak strain.</p><p>Discussion</p><p>Raw minced pork was the most likely infection vehicle in this first reported outbreak caused by O4 non-agglutinating, mostly chloramphenicol-resistant <i>S</i>. Typhimurium DT193. High hospitalization proportions demand awareness on the risk of consumption of raw pork among elderly. LPS analysis indicated O4 expression; therefore, testing with antisera from different lots is recommendable in unexpected agglutination reactions.</p></div

Silver-stained SDS-gel of LPS.

<p>Lanes: 1) protein ladder, 2)– 5) smooth isolates of outbreak strain, 6) rough isolate of outbreak strain, 7) biphasic <i>S</i>. Typhimurium control strain NTCC12023, 8) monophasic <i>S</i>. Typhimurium control strain 06–01900.</p