Chan-Mook Kim

A study on the body attachment stiffness for the road noise

The ride and noise characteristics of a vehicle are significantly affected by the vibration transferred to the body through the chassis mounting points in the engine and suspension. It is known that body attachment stiffness is an important factor of idle noise and road noise for NVH performance improvement. The body attachment stiffness serves as a route design aimed at isolating the vibration generated inside the car due to the exciting force of the engine or road. The test result of the body attachment stiffness is shown in the FRF curve data; the stiffness level and sensitive frequency band are recorded by the data distribution. The stiffness data is used for analyzing the parts that fail to meet the target stiffness at a pertinent frequency band. The analysis shows that the target frequency band is between 200 and 500 Hz. As a result of the comparison in a mounted suspension, the analysis data is comparable to the test data. From these results, there is a general agreement between the predicted and measured responses. This procedure makes it possible to find the weak points before a proto car is produced, and to suggest proper design guidelines in order to improve the stiffness of the body structure.

Optimal Shape Design of an Air-Conditioner Compressor-Mounting Bracket in a Passenger Car

An air-conditioner compressor-mounting bracket is a structural component of an engine, on which bolts attach an air-conditioner compressor. In this paper, the shape of the air-conditioner compressor-mounting bracket of a passenger car is optimized using a finite element software, and the optimized bracket is manufactured and verified by tests. An objective function for the shape optimization of the bracket is the weight of the bracket. Two design constraints on the bracket are the first resonant frequency of the compressor assembly and the need not to fracture during the workbench durability test. The compressor assembly, which consists of a compressor, a bracket and connection bolts, is modeled using finite elements. The bracket is modeled by solid elements and the swash-plate-type compressor is represented by rigid masses and beam elements in order to consider the elastic effects of the compressor. For simulation of the dynamics stresses in the durability test, the large mass method is used. The design variable is the shape of the bracket including thickness profiles of the front and back surfaces of the bracket, radius of outer boltholes, and side edge profiles. The coordinates of the FE nodes control the shape parameters. Optimal shapes of the bracket are obtained by using SOL200 of MSC/NASTRAN. The verification tests are conducted on the workbench and in af ull vehicle. Test results shows that the developed optimization procedure of the bracket are valid in the complex real world.

Study on the Prediction Technique of Vehicle Performance Using Parameter Analysis

With the development of the auto industry, the automobile manufacturers demand to shorten development period and reduce the cost. Compared with the traditional method, applying the virtual prototype is more economical. This paper presents a method for parameters sensitivity analysis and optimizing the performance of vehicle noise and vibration. The existing design processes were repeatedly analyzed with a focus on vehicle performance to decide the design parameters of dimension, thickness, mounting type of body and chassis systems in the vehicle development period. This paper describes the prediction technique of vehicle performance using L18 orthogonal array layout, quality deviation analysis and parameter sensitivity analysis for robust design. This paper analyzed the performance correlation equation through the frequency and sensitivity database according to a design factor change. The new concept is that the performance prediction is possible without repeated activities of test and analysis. This paper described the parameter analysis applications such as bush dynamic stiffness and bush void direction of rear suspension. Design engineer could efficiently decide the design variable using parameter analysis database in early design stage. These improvements can reduce man hour and test development period as well as to achieve stable NVH performance.

Noise Sensitivity Analysis of an Engine Mount System Using the Transfer Function Synthesis Method

The transfer function synthesis method is one of the most powerful methods in analyzing the responses of complex built-up structures under high modal density. Its superiority mostly comes from the ability to incorporate experimental FRFs into the formulation. In this paper, a general procedure for the design sensitivity analysis of vibro-acoustic problems has been presented in frame of the transfer function synthesis method. For an acoustic response function, the proposed method gives a parametric design sensitivity expression in terms of the partial derivatives of the connection element properties and the transfer functions of the substructures. As a realistic problem, an interior noise problem in a passenger car is analyzed. The proposed noise sensitivity formulation calculates the interior noise variations with respect to the changes of the dynamic characteristics of the engine mounts and the bushes. To obtain the FRFs, a finite element model is built for the engine mount structures, and experimental FRFs are used for the trimmed body including cabin cavity. The comparison of interior noise sensitivities obtained by the proposed method and the finite difference method shows that the proposed method is efficient and accurate.

Study on the Analysis Process of the Damping Material for Reduced Floor Vibration

This paper describes the design process of floor damping material optimization to reduce structure borne noise. This process uses finite element analysis(FEA) along with experimental techniques to complement each other. The objective of this approach was to develop an optimized damping material application layout and thickness at the initial design stage. The first step is to find the sensitivity areas of vehicle body without damping material applied using FEA. In order to determine the high vibration areas of the floor panel, the velocity was measured using a scanning laser vibrometer from 20 Hz to 300 Hz. To excite the floor panel vibration, shaker was placed at the front suspension attachment point. The second step is the optimization process to determine the light weight solution of damping material. The design guideline of damping material was suggested that the lightweight solution was verified using test result of road noise. Design engineer could efficiently decide the design variable of damping material using parameter analysis results in early design stage.

Study on the Sound Quality Evaluation Method for the Vehicle Diesel Engine Noise

The brand sound of vehicle diesel engine is recently one of the important advantage strategies in the automotive company. Because various noise components masked under high frequency level can be audible in quieter driving situation. Many researches have been carried out for subjective and objective assessments on vehicle sounds and noises. In particular, the interior sound quality has been one of research fields that can give high quality feature to vehicle products. Vehicle interior noise above 500 Hz is usually controlled by sound package parts. The materials and geometries of sound package parts directly affect on this high frequency noise. This paper describes the sound quality evaluation method for the vehicle diesel engine noise to establish objective criteria for sound quality assessment. Considering the sensitivity of human hearing to impulsive sounds such as diesel noise, the human auditory mechanism was simulated by introducing temporal masking in the time domain. Furthermore, each of the human auditory organs was simulated by computer codes, providing reasonable analytical explanations of typical human hearing responses to diesel noise. This method finally provides the sound quality index of vehicle diesel engine noise that includes high frequency intermittent offensive sounds caused by impacting excitations of combustion and piston slap.

Design of High Stiffness and Lightweight Body for Stiffness Distribution Ratio

Lightweight body due to the decrease of panel thickness and reinforcing member might cause low stiffness. On the other hand, high stiffness body requires an increase of mass. Front pillar section area has been decreased for increasing the driver`s visual field. Global vehicle stiffness is affected by stiffness distribution ratio between upper part and lower part at a side body structure. This paper describes a process used to evaluate the stiffness distribution ratio based on strain energy. In addition, optimum design schemes are presented for high stiffness and lightweight body structure considering the investigated stiffness distribution ratio.

A Study on the Development of High Stiffness Body for Suspension Performance

This paper describes the development process of high stiffness body for ride and handling performance. High stiffness and light weight vehicle is a major target in the refinement of Passenger cars to meet customers` contradictable requirements between ride and handling performance and fuel economy This paper describes the analysis approach process for high stiffness body through the data level of body stiffness. According to the frequency band. we can suggest the design guideline about lg cornering static stiffness, torsional and lateral stiffness, body attachment stiffness. The ride and handling characteristic of a vehicle Is significantly affected by vibration transferred to the body through the chassis mounting points from front and rear suspension. It is known that body attachment stiffness is an important factor of ride and handling performance improvement. And high stiffness helps to improve the flexibility of bushing rate tuning between handling and road noise. It makes possible to design the good handling performance vehicle and save vehicles to be used in tests by using mother car at initial design stage. These improvements can lead to shortening the time needed to develop better vehicles.

Study on the Design Process to minimize the Weight of the Damping Material

Sound packages and damping materials have been widely applied on the floor to decrease the interior noise of a vehicle. Based on the previous researches on the low-noise vehicles, weight optimization through minimization of damping material usage is required while decreasing mid and high frequency range noise by application of sound packages. This paper describes the analysis process of robust design of vehicle body structure before applying damping materials and focuses on the analysis and test process of the location optimization at the stage of damping material application. A vibration experiment for the analysis of floor panel velocity with respect to the excitation of suspension attachment parts at the underfloor of a vehicle is performed. And through the improvement correlation between FEA and TEST, a design guide to optimize damping materials application in the early design stage is proposed. A research on vibration damping steel sheets and liquid acoustic spray on deadener(LASD) is performed to minimize manufacturing time and to minimize the space for pre-existing asphalt damping materials. As results of this study, panel stiffness is achieved through curved surface panel and bead optimization. And test baseline of optimum design is suggested through damping material optimization. And finally, through re-establishing the analysis process for vibration reduction of vehicle floors and lightweight design of damping materials, it is possible to design damping materials efficiently in the preceding stage of design.