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Brake torque variation is a source of objectionable NVH body/chassis response. Such input commonly results from brake disk thickness variation. The NVH dynamic characteristics of a vehicle can be assessed and quantified through experimental modal testing for determination of mode resonance frequency, damping property, and shape. Standard full vehicle modal testing typically utilizes a random input excitation into the vehicle frame or underbody structure. An alternative methodology was sought to quantify and predict body/chassis sensitivity to brake torque variation. This paper presents a review of experimental modal test methodologies investigated for the reproduction of vehicle response to brake torque variation in a static laboratory environment. Brake caliper adapter random and sine sweep excitation input as well as body sine sweep excitation in tandem with an intentionally locked brake will be detailed.

NVH targets for future vehicles are often defined by utilizing a competitive benchmarking vehicle in conjunction with an existing production and/or reference vehicle. Mode management of full vehicle modes is one of the most effective and significant NVH strategies to achieve such targets. NVH dynamic characteristics of a full vehicle can be assessed and quantified through experimental modal testing for determination of global body mode resonance frequency, damping property, and mode shape. Major body modes identified from full vehicle modal testing are primarily dominated by the vehicle's body-in-white structure. Therefore, an estimate of BIW modes from full vehicle modes becomes essential, when only full vehicle modes from experimental modal testing exist. Establishing BIW targets for future vehicles confines the fundamental NVH behavior of the full vehicle.

Tailor welded steel blanks have long been applied in stamping of automotive parts such as door inner, b-pillar, rail, sill inner and liftgate inner, etc. However, there are few known tailor welded aluminum blanks in production. Traditional laser welding equipment simply does not have the capability to weld aluminum since aluminum has much higher reflectivity than steel. Welding quality is another issue since aluminum is highly susceptible to pin holes and undercut which leads to deterioration in formability. In addition, high amount of springback for aluminum panels can result in dimension control problem during assembly. A tailor-welded aluminum blank can help reducing dimension variability by reducing the need for assembly. In this paper, application of friction stir and plasma arc welded blanks on a liftgate inner will be discussed.

Brake judder, which is a low frequency excitation of the suspension and thus, the body structure during low-G braking, is mainly felt at the steering wheel and throughout the vehicle structure. Brake judder is a problem that costs manufacturers millions of dollars in warranty cost and undesirable trade offs. The magnitude of judder response depends not only on the brake torque variation, but also on the suspension design character-istics. This paper discusses the judder simulation process using ADAMS software to investigate the suspension design sensitivity to the first order brake judder performance. The paper recommends “tuning knobs” to suspension designers and vehicle development engineers to resolve issues in the design and development stages. Various suspension design varia-bles including geometry and compliances as well as brake related characteristics were investigated.

To mitigate head impact injuries of vehicle occupants in impact accidents, the FMVSS 201 requires padding of vehicle interior so that under the free-moving-head-form impact, the head injury criterion (HIC) is below the limit. More recently, pedestrian head impact on the vehicle bonnet has been a subject being studied and regulated as requirements to the automobile manufacturers. Over the years, the square wave has been considered as the best waveform for head impacts, although it is impractical to achieve. This paper revisits the head impact topic and challenges the optimality of aiming at the square waveform. It studies several different simple waveforms, with the objective to achieve minimal HIC or minimal crush space required in head-form impacts. With that it is found that many other waveforms can be more efficient and more practical than the square wave, especially for the pedestrian impact.

In the development of several outside mirror designs for vehicles, a high frequency noise (whistling) phenomenon was experienced. First impression was that this might be due to another source on the vehicle (such as water management channels) or a cavity noise; however, upon further investigation the source was found to be the mirror housing. This “laminar whistle” is related to the separation of a laminar boundary layer near the trailing edges of the mirror housing. When there is a free stream impingement on the mirror housing, the boundary layer starts out as laminar, but as the boundary layer travels from the impingement point, distance, speed, and roughness combine to trigger the transition turbulent. However, when the transition is not complete, pressure fluctuations can cause rapidly changing flow patterns that sound like a whistle to the observer. Because the laminar boundary layer has very little energy, it does not allow the flow to stay attached on curved surfaces.

Knowledge of the loads experienced by a leaf spring suspension is required for the optimal design of the suspension components and frame. The most common method of representing leaf springs is the SAE 3 link model, which does not give good results in the lateral direction. In this paper, a beam element leaf spring model is developed. This model is validated using data obtained from laboratory tests done on leaf spring assemblies. The model is then subjected to actual road load data measured on the Proving Ground. Lastly, results from the beam element model are presented and compared with results obtained from proving ground tests. Overall, the beam element model gives good results in all directions except in situations where it is subjected to high fore/aft acceleration and high reverse braking events.

In this paper, a comprehensive evaluation index for impact harshness (IH) is proposed. A mid-sized uni-body SUV is selected for this study, with the acceleration responses at the various vehicle body locations as objective functions. A sensitivity study is conducted using an ADAMS full vehicle model with flexible body structure representation over an IH event to analyze the influence of various suspension tuning parameters, including suspension springs, shock damping, steer gear ratio, unsprung mass, track-width, and bushing stiffness.

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.

In this paper, mechanism of fastened joints is described; numerical analyses and testing calibrations are conducted for the possible simplified finite element simulation approaches of the joints; and the best simplified approach is recommended. The approaches cover variations of element types and different ways that the joints are connected. The element types include rigid elements, deformable bar elements, solid elements, shell elements and combinations of these element types. The different ways that the joints are connected include connections of one row of nodes, two row of nodes and alternate nodes in the first and second rows. These simplified simulation approaches are numerically evaluated on a joint of two plates connected by a single fastener. The fundamental loads, bending with shear, shear and tension are applied in the numerical analyses. A detailed model including contact and clamp load are analyzed simultaneously to provide “accurate results”.

Over the past five years, the US Automotive Materials Partnership (USAMP) has brought together representatives from DaimlerChrysler, General Motors, Ford Motor Company and over 40 other participant companies from the Mg casting industry to create and test a low-cost, Mg-alloy engine that would achieve a 15 - 20 % Mg component weight savings with no compromise in performance or durability. The block, oil pan, and front cover were redesigned to take advantage of the properties of both high-pressure die cast (HPDC) and sand cast Mg creep- resistant alloys. This paper describes the alloy selection process and the casting and testing of these new Mg-variant components. This paper will also examine the lessons learned and implications of this pre-competitive technology for future applications.

This paper describes a lightweight magnesium intensive automobile body structure concept developed at DaimlerChrysler to support a high fuel-efficiency vehicle project. This body structure resulted in more than 40% weight reduction over a conventional steel structure while achieving significantly improved structural performance as evaluated through CAE simulations. A business case analysis was conducted and showed promising results. One concept vehicle was built for the purpose of demonstrating concept feasibility. The paper also identifies areas for further development to enable such a vehicle to become a production reality at a later time.

The popularity of AWD passenger vehicles presents a challenge to provide car-like drive-train NVH within a relatively small package space. This paper describes a drive-train NVH case study in which analysis and test were used, in conjunction, to solve an NVH problem. Also, it details a systematic process of using the analytical model to identify and resolve similar problems. The particular problem for this case study is a noise and vibration issue occurring at 75 MPH primarily in the middle seat of an all-wheel drive vehicle. Tests indicated that it may be due to propeller shaft imbalance. Analysis results showed good correlation with the tests for that loading condition. Several solutions were identified, which were confirmed by both test and analysis. The most cost-effective of these solutions was implemented.

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.

This paper introduces a reliable method to calculate body mount loads from wheel-force-transducer (WFT) measurements on framed vehicles. The method would significantly reduce time and cost in vehicle development process. The prediction method includes two parts: Hybrid Load Analysis (HLA) that has been used by DaimlerChrysler Corporation and Body Mount Load Analysis (BMLA) that is introduced by this paper for the first time. The method is validated on a body-on-frame SUV and a pickup truck through one proving ground events. The example shown in this paper is for a SUV and one of the most severe events. In HLA, the loads at suspension-to-frame attachments are calculated from spindle loads measured by WFT. In BMLA, body mount loads were calculated using outputs of HLA with detailed finite-element-modeled frame and body. The loads are compared with measured body mount loads. The comparisons are conducted in range, standard deviation (S.D.), and fatigue pseudo-damage.

Advanced material modeling was conducted to describe the thermal-mechanical behavior of Boron Steel during hot stamping, a process in which blanks at 900 °C are formed and quenched between cold dies. Plastic deformation, thermal dilatation and phase transformation were incorporated in the constitutive model and a user-defined subroutine was developed to interface with LS-DYNA. Simulation was conducted on the hot stamping process of a door intrusion beam to gain insight into the physics of the process. Results showed significant influence of the thermal cycle on final product. It was also demonstrated that the program developed can be used as an early feasibility tool to determine baseline processing parameters and to detect potential defects in products without physical prototyping.

Buffeting is a wind noise of high intensity and low frequency in a moving vehicle when a window or sunroof is open and this noise makes people in the passenger compartment very uncomfortable. In this paper, side window buffeting was simulated for a typical SUV using the commercial CFD software Fluent 6.0. Buffeting frequency and intensity were predicted in the simulations and compared with the corresponding experimental wind tunnel measurement. Furthermore, the effects of several parameters on buffeting frequency and intensity were also studied. These parameters include vehicle speed, yaw angle, sensor location and volume of the passenger compartment. Various configurations of side window opening were considered. The effects of mesh size and air compressibility on buffeting were also evaluated. The simulation results for some baseline configurations match the corresponding experimental data fairly well.

The US Automotive Materials Partnership (USAMP) and the US Department of Energy launched the Magnesium Powertrain Cast Components Project in 2001 to determine the feasibility and desirability of producing a magnesium-intensive engine; a V6 engine with a magnesium block, bedplate, oil pan, and front cover. In 2003 the Project reached mid-point and accomplished a successful Decision Gate Review for entry into the second half (Phase II) of the Project. Three tasks, comprising Phase I were completed: (1) evaluation of the most promising low-cost, creep-resistant magnesium alloys, (2) design of the engine components using the properties of the optimized alloys and creation of cost model to assess the cost/benefit of the magnesium-intensive engine, and (3) identification and prioritization of scientific research areas deemed by the project team to be critical for the use of magnesium in powertrain applications.

Once the design of a door sheetmetal and accessories is confirmed, the acoustics of the door system depends on the sound package assembly. This essentially consists of a watershield which acts as a barrier and a porous material which acts as an absorber. The acoustical performance of the watershield and the reverberant sound build-up in the door cavity control the performance. This paper discusses the findings of a design study that was developed based on design of experiments (DOE) concepts to determine which parameters of the door sound package assembly are important to the door acoustics. The study was based on conducting a minimum number of tests on a five factor - two level design that covered over 16 different design configurations. In addition, other measurements were made that aided in developing a SEA model which is also compared with the findings of the results of the design study.

This paper dis cusses the development of a nonlinear shock absorber model for low-frequency CAE-NVH applications of body-on-frame vehicles. In CAE simulations, the shock absorber is represented by a linear damper model and is found to be inadequate in capturing the dynamics of shock absorbers. In particular, this model neither captures nonlinear behavior of shock absorbers nor distinguishes between compression and rebound motions of the suspension. Such an inadequacy limits the utility of CAE simulations in understanding the influence of shock absorbers on shake performance of body-on-frame vehicles in the low frequency range where shock absorbers play a significant role. Given this background, it becomes imperative to develop a shock absorber model that is not only sophisticated to describe shock absorber dynamics adequately but also simple enough to implement in full-vehicle simulations. This investigation addresses just that.