Applied Mechanics and Materials Vol. 471

Abstract: This paper aims to investigate the coupling resonance conditions of the tyre, cavity and rim with the attachment of trim layers on the inner surface of tyre to mitigate the resonance effect. In order to validate the mathematical formulation, finite element analysis and experimental modal testing were performed to determine the frequency response function (FRF) for a tyre-wheel assembly with and without the trim layers as well as for separated tyre and rim. It was found that the resonance magnitude has been reduced when the trim layers were added. Couplings of cavity resonance to the tyre and rim were plausible due to the proximity of their resonance frequencies. Trim materials were tested using an impedance tube to suggest the best sound absorbing materials that can be used to mitigate the tyre cavity resonance effect.

Abstract: Inerter is a recent element in suspension systems with the property that the generated force is proportional to the relative acceleration between its two terminals, which is similar to the way a spring reacts to relative displacement and a damper to relative velocity. This paper presents the analysis of a non-linear inerter working in parallel to passive spring and damper of a vehicle suspension to evaluate its effect on vehicles ride. The non-linear inerter was theoretically capable of switching between on and off states depending on whether or not the suspension deflection was beyond a specified free play. In the study, this behavior was represented mathematically as control law which depended on the relative displacement between the sprung and unsprung masses. A mathematical quarter vehicle model incorporating the non-linear inerter was simulated in MATLAB/Simulink to determine the vehicle responses due to road input in the form of step profile for different combinations of free play and inerters on-state proportionality constant called the inertance. Results showed improvements in vehicle ride comfort, as demonstrated by the lower root-mean-squared sprung mass accelerations compared to the ordinary passive suspension with only spring and damper. Additionally, implementation of non-linear inerter gave lower percentage overshoot to step input, indicating better transient response than ordinary passive suspension.

Abstract: This paper investigates the effect of vibration and vehicle body movements acting on the vehicles wheel due to the different damping characteristics of suspension systems. Three different damping characteristics damper named Absorber A, Absorber B and Absorber C was installed on the suspension system of the Proton Persona which was used as a test car. This test car was equipped with accelerometers and wire potentiometer sensor on the front and rear suspensions, gyroscopic, Global Positioning System (GPS) and connect with DEWEsoft software as a data acquisition. To study the effect of three different damper characteristics on suspension system, the ride comfort analysis and car body movement analysis were used to analyze the result during experimental testing. There were 3 maneuver testing experiment were performed including steady-state cornering, single-lane change and slalom testing experiment. Based on the results, comparison between the suspension damper characteristics due to the driving maneuvers and car movement were made and their performance also were ranked. Absorber A was the hardest damper as compared to Absorber C and Absorber B according to the damping constant value. The result showed that the best performance for car movement made by Absorber A then followed by Absorber C and Absorber B, while the best performance for ride comfort analysis was made by Absorber B followed by Absorber C and A.

Abstract: Drum brake squeal is one of the most common and annoying types of brake noise and it usually falls in the frequency range between 0.5-16 kHz. Brake squeal continues to confront vehicle manufacturers where it not only leads to significant increase in the warranty costs but also may affect customers perception on quality of the vehicle. Thus this paper attempts to prevent drum brake squeal by means of lining modifications. In doing so, finite element method is first employed and squeal noise will be then predicted using complex eigenvalue (CE) analysis. A good lining modification should be able to stabilize the drum brake assembly by shifting or reducing positive real parts toward zero or negative real parts in the eigenvalue analysis. Finally, laboratory squeal tests are conducted on the four proposed modifications to verify its effectiveness against squeal.

Abstract: Brake judder is defined as disc or drum deformation-induced vibration which typically occurs at frequency less than 200 Hz. There are two types of brake judder namely, low speed (cold) judder and high speed (hot) judder. These two types of judder are often causing the brake pedal, steering wheel, suspension or chassis to vibrate. Consequently, it will affect comfort level of the driver and passengers. This paper focuses on the experimental investigation of low speed brake judder. In doing so, a laboratory test rig consists of disc brake unit, steering and suspension systems was used to assess level of brake judder vibration at different wheel turning angles. It was found that brake judder generated slightly high vibration at the steering wheel in the axial direction which led to a little uncomfortable feeling to the driver.

Abstract: The effectiveness of vibration isolator or mount can be done by quantifying the vibration energy flow through the isolators. This can provide information on the quantification of the vibration energy flow from the powertrain to the structure or chassis. Vibration energy flow through mount is identified as vibration power flow that is one of vibration transmission paths. This paper presents vibration power flow through four elastomeric mount. The vibration (source and receiver of accelerations) was measured by running engine at constant speed and without load conditions in varying speeds starting from 1050 RPM to 4000 RPM. The vibration was measured only in z-direction (vertical direction). The noise inside compartment was measured at the condition of engine run-up without load condition and was measured starting from 1050 RPM to 4000 RPM engine speed. The results from vibration power flow analysis showed that the main vibration energy transmission was high from front mount and rear mount, around engine speed 3200 RPM, and booming noise occurred around 3200 RPM due to structure-borne noise.

Abstract: An acoustic analysis in the investigation of brake noise shows the severity of the noise and its characteristics and a vibration analysis shows the excitations of noise that is present in the braking event. In this study, vibration and acoustic analyses were used to study the brake noise which is produced during braking. Vibration and acoustic data were collected simultaneously during braking to identify the braking condition. The data analysis focuses on the low frequency domain. The Fast Fourier method was used to analyse the vibration and acoustic signals. The computation of FFT was done independently and the frequency domains obtained were compared. The parallelism in the analysis was used to identify the acoustic source. The determination of the source will aid in brake noise reduction efforts and reinforce the vibration analysis method as a system identification method for brake noise.

Abstract: Vehicle acoustical comfort and vibration in a passenger car cabin are the main factors that attract a buyer in car purchase. Numerous studies have been carried out by automotive researchers to identify and classify the acoustics level in the vehicle cabin. The objective is to form a special benchmark for acoustics level that may be referred for any acoustics improvement purpose. This study is focused on the sound quality change over the engine speed [rp to recognize the noise pattern experienced in the vehicle cabin. Since it is difficult for a passenger to express, and to evaluate the noise experienced or heard in a numerical scale, a neural network optimization approach is used to classify the acoustics levels into groups of noise annoyance levels. A feed forward neural network technique is applied for classification algorithm, where it can be divided into two phases: Learning Phase and Classification Phase. The developed model is able to classify the acoustics level into numerical scales which are meaningful for evaluation purposes.

Abstract: Current vehicle development period has become shorter; therefore, virtual testing has been considered as vital to assist design decision at the early stage of the development. Over the last three decades, Finite Element Method (FEM) is widely used to predict the Noise and Vibration level of a vehicle. With the latest technology of Computer Aided Engineering (CAE) simulation, the calculation time taken for NVH analysis can be reduced from few days to only few hours. This paper presents current simulation technique for automotive development using Altair Hyperworks as preprocessing tool for vehicle modeling as well as application of NASTRAN as calculation solver. Normal Mode analysis is conducted on the Trimmed Body to investigate the natural frequency of the steering and the vehicle resonance. The result obtained is comparable with the actual prototype testing result to present the level of correlation. Coupling structural-acoustic analysis also conducted to predict the Noise Transfer Function (NTF) at the driver's ear.