Tribological And Dynamical Study Of An Automotive Transmission System

The transmission system is critical for automotive and heavy duty equipment due to its prominent role in the powertrain system, which is often challenged with degraded torque capacity and harsh dynamic response. Simulation-guided design can provide appropriate guidelines to resolve these problems with virtual analyses. In current study, the tribological and dynamical study of an automatic transmission is performed at two levels: a wet clutch and powertrain. In this dissertation, tribological study is performed for a wet clutch based on the thermohydrodynamic (THD) analysis that takes the following factors into account. • The groove effect (depth, area, and pattern) is investigated for lubrication analysis; • The elastic-plastic asperity contact model is used to predict the contact pressure; • The heat transfer during the entire cycle of engagement from slip to lock to detachment is covered; • The engagement time and the temperature profile are predicted for torque and thermal analysis. With large engagement cycles, the friction lining of a wet clutch is worn off due to the material degradation at high load/temperature condition. By relating the wear behavior with the mechanism of thermal degradation and thermomechanical degradation, a physics-based wear model is proposed for the first time to analyze the wear process in a wet clutch. The predicted wear rate falls within nearly 95% confidence interval of the test results. Discrepancies of simulation are primarily due to limited availability of input data and model assumptions. Therefore, an uncertainty quantification analysis of the wear model is performed using the Monte Carlo simulations. In addition, a comprehensive parametric analysis of the clutch wear is considered with various factors, including groove design (waffle pattern shows the minimum wear), material properties and operational configurations (rotational speed plays the most influential role). The dynamics of transmission directly affects the performance of the powertrain. The coupling effects of the key transmission components are examined. Of particular interests are the stick-slip behavior of the wet clutch and backlash of the gear train. Through simulation of the powertrain, the main source and the pattern of vibration propagation in the driveline are examined. Major vibration is observed during inappropriate clutch engagement

Structural dynamics branch research and accomplishments to FY 1992

This publication contains a collection of fiscal year 1992 research highlights from the Structural Dynamics Branch at NASA LeRC. Highlights from the branch's major work areas--Aeroelasticity, Vibration Control, Dynamic Systems, and Computational Structural Methods are included in the report as well as a listing of the fiscal year 1992 branch publications

MultiBody Dynamic Analysis of a 3D Synchronizer Model

L'abstract è presente nell'allegato / the abstract is in the attachmen

Elastohydrodynamic Analysis of Spur Gears Using Load-Sharing Concept: Running-In and Steady-State

Gears are widely used in industry and hence their performance is of vital importance. Under the typical operating conditions of gears, the lubricant layer formed between the teeth of the pinion and the gear cannot completely separate the surfaces and contact of asperities of the pinion and gear occurs. This case is usually referred to as mixed lubrication problem. In this research the load-sharing concept has been employed to predict the performance of the pinion-gear system. The load-sharing concept is an efficient method to solve the mixed lubrication problem and is capable to predict the thickness of the lubricant film, contribution of the fluid film and asperities in carrying the load, friction coefficient, lubricant temperature, and wear with fairly good accuracy. During the initial stage of contact, a considerable number of plastic contact occurs between asperities resulting in permanent change of surface roughness profile. This period which is called running-in has a significant effect on the steady-state performance of the pinion-gear system. The developed model has the capability to predict the variation of surface roughness and contribution of fluid film as well as asperities in carrying the load during running-in. The steady-state wear of gears is predicted using the thermal desorption model. A test rig is designed and built which is capable to mimic the operating condition of any point on the involute profile of gear. Two motors are used to rotate the rollers to generate the same rolling and sliding speed as the corresponding point of the involute profile of pinion-gear system. A hydraulic system is used to exert the desired load on the rollers and keep them in contact under the applied load. The sensors that are mounted on this test rig monitor the speed of each shaft, applied load, surface temperature, and wear depth. The results of the experiments that are conducted on the fresh rollers as well as broken-in roller are shown to be in good agreement with the predicted running-in behavior and steady-state behavior, respectively

Tribology: The Story of Lubrication and Wear

Topics addressed include: lubrication and design of high speed rolling element bearings, high speed gears, and traction drives

Helical gear wear monitoring: Modelling and experimental validation

Gear tooth surface wear is a common failure mode. It occurs over relatively long periods of service nonetheless, it degrades operating efficiency and leads to other major failures such as excessive tooth removal and catastrophic breakage. To develop accurate wear detection and diagnosis approaches at the early phase of the wear, this paper examines the gear dynamic responses from both experimental and numerical studies with increasing extents of wear on tooth contact surfaces. An experimental test facility comprising of a back-to-back two-stage helical gearbox arrangement was used in a run-to-failure test, in which variable sinusoidal and step increment loads along with variable speeds were applied and gear wear was allowed to progress naturally. A comprehensive dynamic model was also developed to study the influence of surface wear on gear dynamic response, with the inclusion of time-varying stiffness and tooth friction based on elasto-hydrodynamic lubrication (EHL) principles. The model consists of an 18 degree of freedom (DOF) vibration system, which includes the effects of the supporting bearings, driving motor and loading system. It also couples the transverse and torsional motions resulting from time-varying friction forces, time varying mesh stiffness and the excitation of different wear severities. Vibration signatures due to tooth wear severity and frictional excitations were acquired for the parameter determination and the validation of the model with the experimental results. The experimental test and numerical model results show clearly correlated behaviour, over different gear sizes and geometries. The spectral peaks at the meshing frequency components along with their sidebands were used to examine the response patterns due to wear. The paper concludes that the mesh vibration amplitudes of the second and third harmonics as well as the sideband components increase considerably with the extent of wear and hence these can be used as effective features for fault detection and diagnosis

Thermo-elastohydrodynamics of hypoid gears with formulated lubricants

One of the main design criteria currently used by the automotive industry us that of designing fuel efficient vehicles. Strict regulations imposed within the European Union and the United States, dictate progressively lower limits of greenhouse gases emissions, either via imposed taxation or, in extreme cases via refraining the distribution of certain vehicle models. Friction itself is one of the sources responsible for increased fuel consumption. Consequently, its understanding on a full scale system level is of essential importance in employing improved design methodologies and fuel efficient lubricants. The present study focuses its attention on the theoretical prediction of the power losses and the conjunctional efficiency of hypoid gear pairs which are located in the differential units of modern cars. Particular attention is paid on the effect of the lubricant formulation on the efficiency performance of the system. This is realised through the rheological characterisation of the lubricating oil under well controlled laboratory conditions, such as those appearing in viscometers. A total of 6 gear lubricants of the same viscosity grade (SAE 75W-90), blended with the same additive pack are examined. The key difference between each lubricant is on the type and the concentration of the Viscosity Modifier (VM). The viscosity of each fluid is characterised for high temperature, high pressure and high shear rate, conditions usually encountered in the Elastohydrodynamic (EHD) conjunctions of highly loaded hypoid gears. The conjunctional efficiency of three different hypoid gear pair geometries is examined under the influence of different lubricant formulation. The actual contact geometry of each gear-set is captured through a quasi-static Finite Element (FE) procedure known as Tooth Contact Analysis (TCA). The torsional gear dynamics of the gear pair are also captured through a 4 Degree of Freedom (DoF) lumped parameter model, highlighting the impact of the inertial properties of the system on its efficiency performance.</div

Tribology of power train systems

Tribology of power train system

Condition Monitoring of Helical Gear Transmissions Based on Vibration Modelling and Signal Processing

Condition monitoring (CM) of gear transmission has attracted extensive research in recent years. In particular, the detection and diagnosis of its faults in their early stages to minimise cost by maximising time available for planned maintenance and giving greater opportunity for avoiding a system breakdown. However, the diagnostic results obtained from monitored signals are often unsatisfactory because mainstream technologies using vibration response do not sufficiently account for the effect of friction and lubrication. To develop a more advanced and accurate diagnosis, this research has focused on investigating the nonlinearities of vibration generation and transmission with the viscoelastic properties of lubrication, to provide an in-depth understanding of vibration generating mechanisms and hence develop more effective signal processing methods for early detection and accurate diagnosis of gear incipient faults. A comprehensive dynamic model has been developed to study the dynamic responses of a multistage helical gear transmission system. It includes not only time-varying stiffness but also tooth friction forces based on an elastohydrodynamic lubrication (EHL) model. In addition, the progression of a light wear process is modelled by reducing stiffness function profile, in which the 2nd and 3rd harmonics of the meshing frequency (and their sidebands) show significant alteration that support fault diagnostic at early stages. Numerical and experimental results show that the friction and progressive wear induced vibration excitations will change slightly the amplitudes of the spectral peaks at both the mesh frequency and its sideband components at different orders, which provides theoretical supports for extracting reliable diagnostic signatures. As such changes in vibrations are extremely small and submerged in noise, it is clear that effective techniques for enhancing the signal-to-noise ratio, such as time synchronous averaging (TSA) and modulation signal bispectrum (MSB) are required to reveal such changes. MSB is preferred as it allows small amplitude sidebands to be accurately characterised in a nonlinear way without information loss and does not impose any addition demands regarding angular displacement measurement as does TSA. With the successful diagnosis of slight wear in helical gears, the research progressed to validate the capability of MSB based methods to diagnose four common gear faults relating to gear tribological conditions; lubrication shortfall, changes in lubrication viscosity, water in oil, and increased bearing clearances. The results show that MSB signatures allows accurate differentiation between these small changes, confirming the model and signal processing proposed in this thesi