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This paper describes the process used to develop an experimental model with forward prediction capabilities for passenger vehicle axle whine performance, focusing initially on beam axle design modifications. This process explains how experimental Transfer Path Analysis (TPA), Running Modes Analysis (RMA) and Modal Analysis were used along with an experimental FRF-Based Substructuring (FBS) model. The objective of FBS techniques is to predict the dynamic behavior of complex structures based on the dynamic properties of each component of the structure. The FBS model was created with two substructures, the body/suspension and the empty rear beam axle housing. Each step in the creation of the baseline FBS model was correlated, and the forward predictive capability was verified utilizing an experimental modification to the beam axle structure.

This paper summarizes a study on axle balance measurement and balancing strategies. Seven types of axles were investigated. Test samples were randomly selected from products. Two significant development questions were set out to be answered: 1) What is the minimum rotational speed possible in order to yield measured imbalance readings which correlated to in-vehicle imbalance-related vibration. What is the relationship between the measured imbalance and rotational speed. To this end, the imbalance level of each axle was measured using a test rig with different speeds from 800 to 4000 rpm with 200 rpm increments. 2) Is it feasible to balance axle sub-assemblies only and still result in a full-assembly that satisfies the assembled axle specification? To this end, the sub-assemblies were balanced on a balance machine to a specified level. Then with these balanced sub-assemblies, the full assemblies were completed and audited on the same balance test rig in the same way.

In automotive testing, a chassis dynamometer is typically used, during cell testing, to evaluate vehicle performance by simulating actual driving conditions. The use of indoor cell testing has the advantage of running controlled tests where the cell temperature and humidity and solar loads can be well controlled. Driving conditions such as vehicle speed, wind speed and grade can be also controlled. Thus, repeated tests can be conducted with minimum test variations. The tractive effort required at the wheels of a vehicle for a given set of operating parameters is determined by taking into account a set of variables which affect vehicle performance. The forces considered in determination of the tractive effort include the constant friction force, variable friction force due to mechanical and tire friction, forces due to inertia and forces due to aerodynamic and wind effects. In addition, forces due to gravity are considered when road grades are simulated.

One of the major NVH concerns for automobile manufacturers is the response of a vehicle to the impact of the tire as it encounters a road discontinuity or bump. This paper describes methods for analyzing the impact response of a vehicle to such events. The test vehicle is driven on a dynamometer, on which a bump simulating cleat is mounted. The time histories of the cleat impact response of the vehicle can be classified as a transient and a repeated signal, which should be processed in a special way. This paper describes the related signal processing issues, which include converting the time data into a continous spectrum, determination of the correct scaling factor for the analyzed spectrum, and smoothing out harmonics and fluctuations in the signal. This procedure yields a smooth frequency spectrum with a correctly scaled amplitude, in which the frequency contents can be easily identified.

Over 250 million tires are scrapped in the United States each year. Tires have been a problematic scrap because they have been designed to resist destruction, and have a tendency to float upwards in landfills. Improper storage has resulted in tire fires1--an even more problematic environmental concern than unsightly piles which can serve as breeding grounds for insect vectors. A better solution is to recover materials for use in new components. Not only does this resolve the landfill issue, but it also serves to conserve resources, while returning an economic benefit to society. This paper traces the introduction of tire material recovery at NRI Industries and DaimlerChrysler Corporation (DCC), the development of the infrastructure and materials, and the launch of the Jeep Grand Cherokee thermoplastic elastomer (TPE) radiator seals, comprised of post consumer tire crumb.

A traction test machine, developed for evaluation of traction-CVT fluids for the automotive consortium, USCAR, provides precision traction measurements to stresses up to 4 GPa. The high stress machine, WAMhs, provides an elliptical contact between AISI 52100 steel roller and disc specimens. Machine stiffness and positioning technology offer precision control of linear slip, sideslip and spin. A USCAR traction test methodology includes entrainment velocities from 2 to 10 m/sec and temperatures from -20°C to 140°C. The purpose of the USCAR machine and test methodology is to encourage traction fluid development and to establish a common testing approach for fluid qualification. The machine utilizes custom software, which provides flexibility to conduct comprehensive traction fluid evaluations.

Recently, many authors have attempted to represent an automobile body in terms of experimentally derived frequency response functions (FRFs), and to couple the FRFs with a FEA model of chassis for performing a total system dynamic analysis. This method is called Hybrid FEA-Experimental FRF method, or briefly HYFEX. However, in cases where the chassis model does not include the bushing models, one can not directly connect the FRFs of the auto body to the chassis model for performing a total system dynamic analysis. In other cases when the chassis model includes the bushings, the bushing dynamic rates are modeled as constant stiffness rather than frequency dependent stiffness, the direct use of the HYFEX method will yield unsatisfactory results. This paper describes how the FRF's of the auto body and the frequency dependent stiffness data of the bushings can be combined with an appropriate mathematical formulation to better represent the dynamic characteristics of a full vehicle.

Accurate motion prediction can be used to evaluate vibrations at seat track and steering wheel. This paper presents the prediction and correlation of truck frame motion from wheel force transducer (WFT) measurements. It is assumed that the method can be used to predict vibrations at seat track and steering wheel for unibody vehicles. Two durability events were used for calculation. WFT measurements were used as inputs applied on frame from suspension. Frame loads were then used as inputs to calculate frame motions using a FEA approach. The predicted frame motions are represented by four exhaust hangers and they are compared with measured motions of the same locations. The correlations include displacement, velocity, and acceleration. It is shown that good correlations are obtained in velocity and displacement. Acceleration shows bigger differences than velocity and displacement.

With the ever increasing popularity of SUV automobiles, studies involving driveline specific problems have grown. One prevalent NVH problem is axle whine associated with the assembled motion transmission error (MTE) of an axle system and the corresponding vibration/acoustic transfer paths into the vehicle. This phenomenon can result in objectionable noise levels in the passenger compartment, ensuing in customer complaints. This work explores the methodology and test methods used to diagnose and solve a field axle whine problem, including the use of cab mount motion transmissibility path analysis, running modes and a detailed MTE best-of-the-best (BOB)/worst-of-the-worst (WOW) study. The in-vehicle axle whine baseline measurements including both vehicle dynamometer and on-road test conditions, along with the countermeasures of axle whine fixes are identified and presented in this paper.

In this paper, we study the sensitivity of a vehicle impact harshness (IH) performance to the suspension bushing rates. A mid-sized uni-body SUV is selected for this study, with the acceleration responses at the driver seat track and the steering wheel as objective functions. A sensitivity study is conducted using an ADAMS full vehicle model including a tire model and flexible body structure representation over an IH event. The study resulted in the identification of key bushings that affect the IH performance and its sensitivity to the bushing rates. Based on the results, we came-up with an “optimal” bushing set that minimizes impact harshness, which was subjectively verified to result in significant improvement in IH.

Tire stiffness can have a significant effect on the spindle and component loads. While its’ effect on the component loads may show a different trend. This paper deals with data acquisition loads using Wheel Force Transducer (WFT) with 17 inch, 18 inch and 20 inch tires and shows how the spindle loads changed for different tire. These loads are applied on the analytical suspension model to generate both component and the body attachment loads. Some of the measured channels are correlated for all the wheel sizes for multiple events to ensure the confidence in the model. It is found that even if spindle loads are increased with tire stiffness, the component loads do not necessarily show a similar trend. This paper studies why higher spindle forces do not always give higher component loads and what are the possible alternatives one may look into to shortlist or select one set of loads over the other.

An advancement in traction control has entered the marketplace this year with the debut of the 1999 Jeep® Grand Cherokee equipped with the Quadra-TracII or Quadra-Drive four wheel drive systems. The new technology that is at the heart of these systems is the progressive coupling. A new passive adaptive traction control device that utilizes much of the hardware normally associated with automatic transmissions but applied to enhance traction. In the following report the function of progressive coupling will be described along with design characteristics and parameter recommendations.