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Generally within engineering design, the current emphasis is on biasing the development process towards increased virtual prototyping and reduced “real” prototyping. Therefore there is a requirement for more CAE based automated optimisation, Design of Experiments and Design for Six Sigma. The main requirements for these processes are that the model being analysed is parametric and that the solution time is short. Prediction of gear whine behaviour in automatic transmissions is a particularly complex problem where the conventional FEA approach precludes the rapid assessment of “what if?” scenarios due to the slow model building and solution times. This paper will present an alternative approach, which is a fully parametric functionality-based model, including the effects of and interactions between all components in the transmission. In particular the time-varying load sharing and misalignment in the planetary gears will be analysed in detail.

An application involving noise source reconstruction on a full automotive powerplant including the engine, manifolds and the transmission is considered herein, to demonstrate the versatility of modern generalized acoustical holography. The complex source geometry necessitates measurements on non-conforming surfaces. The acoustic pressures were experimentally acquired at three different engine excitations. Accelerometers were mounted at select locations on the powerplant in order to study the accuracy of the reconstructed vibrations from acoustical holography. Through a series of synthetically generated holograms with added random noise, it is conclusively demonstrated that the error margins in the reconstructed vibrations on the powerplant are consistent with errors in reconstructed vibrations from numerically synthesized holograms of a similar Signal to Noise Ratio (SNR).

The Ford Spin Torsional NVH TEST Facility developed and completed in 1999 as a state-of-the-art powertrain NVH development facility(1). Since then, various designed capabilities have been verified with test vehicles for multiple applications to facilitate powertrain NVH development. This paper describes fundamental capabilities of the test facility, including input module to simulate engine torque signatures of arbitrary engines (“virtual engine” capability) and absorbing dynamometer systems, functioning as a precision 4WD/AWD chassis dynamometer. The correlation between road test/chassis dynamometer test and Spin-Torsional test is then illustrated, verifying high correlation of vehicle/sub-system responses between conventional vehicle testing and Spin-Torsional test results.

Generation mechanism of transmission gear whine varies significantly by gear position, frequency and path/amplifier of the total system. Although controlling the source, namely transmission error/dynamic meshing force of the gears is desirable; it is not always feasible as well as most effective. This paper describes the root cause analyses of high frequency gear whine (overdrive position) of commercial vehicle, which combined in-depth experimental and CAE analyses. The generation mechanism of the gear whine is clarified efficiently utilizing Ford Spin-Torsional AWD NVH Test Facility, state-of-the-art Powertrain NVH development test cell, combining vehicle and sub-system NVH measurement. The analyses results showed the O/D gear whine is driveshaft airborne, due to alignment of driveshaft higher bending resonance to air-borne mode (“breathing mode”).

As the quietness of vehicles has been continually improved in recent years, there have been stronger requirements to reduce transmission gear noise and thereby improve transmission quality. So far efforts to achieve quieter gears have generally focused on ways of reducing the excitation forces of individual gears. In addition to these traditional methods, there is a greater need today to adopt a new approach to gear noise reduction in which improvements are made to the gear train itself as the transmitter of vibration in the transmission. This paper describes the systematic approach taken to reduce the overall gear noise of the new RE4F04A four-speed automatic transaxle.The cross-sectional view is shown in Fig. 1. The vibration characteristics of this automatic transaxle were first identified by finite element analysis, and an investigation was made of a gear train structure that would be effective in reducing gear noise.

In order to effectively evaluate automatic transmission gear noise and vibration performance using a hemi-anechoic test facility, it is essential to understand the coupling mechanism between the transmission internals and the dynamometers and associated shafting. Once this coupling mechanism is well understood, each major frequency response of the resulting torsional vibration operating data can be properly categorized according to the source: transmission-internal, facility, or driveshaft. This knowledge helps noise and vibration engineers properly manage vibration peaks in transmission operating data by ensuring that the issue of concern is not inadvertently influenced by the facility system. Analytical simulations and tests were performed on a transmission operated in a hemi-anechoic facility to evaluate gear vibration using various driveshafts, followed by a program of vehicle testing.

Gear whine can be reduced through a combination of gear parameter selection and manufacturing process design directed at reducing the effective transmission error. The process of gear selection and profile modification design is greatly facilitated through the use of simulation tools to evaluate the details of the tooth contact analysis through the roll angle, including the effect of gear tooth, gear blank and shaft deflections under load. The simulation of transmission error for a range of gear designs under consideration was shown to provide a 3-5 dB range in transmission error. Use of these tools enables the designer to achieve these lower noise limits. An equally important concern is the dynamic mesh stiffness and transmissibility of force from the mesh to the bearings. Design parameters which affect these issues will determine the sensitivity of a transmission to a given level of transmission error.

Effectively managing transmission noise, vibration and harshness (NVH) has become increasingly important for maximizing customer satisfaction and fostering the perception of quality in contemporary cars and trucks. As overall vehicle and engine masking levels have dramatically decreased in recent times, low level tonal noises generated by transmission internals have gained significance and therefore have a greater effect on the NVH performance of vehicles. Recognizing the importance of this trend, Ford Motor Company recently designed and built a state-of-the-art research and development facility to be used for reducing noise and vibration generated by automatic and manual vehicle transmissions. The significant design features and validation results of this facility are described in this paper.