Mohammad Fard

Hydraulic engine mounts: a survey

An ideal engine mount should provide a dual behavior. It needs to be soft to reduce the transmitted force, and to be hard to limit the relative displacement. The constant parameter linear mounts are unable to provide a good isolation when the excitation frequency is variable. Hydraulic engine mounts were invented as smart isolators to passively produce a soft isolator at low amplitude and a hard isolator at high amplitude. Having a dual behavior puts the mounts in the domain of nonlinear systems which in turn causes many new phenomena which have never appeared in linear analysis. The dual behavior hydraulic engine mounts were introduced around 1980 and passed through many analytic and technical improvements. This article will review these improvements up to 2012 and discusses the technical problems and methods of remedy.

Effects of seat structural dynamics on current ride comfort criteria

The ISO 2631-1 (1997) provides methodologies for assessment of the seated human body comfort in response to vibrations. The standard covers various conditions such as frequency content, direction and location of the transmission of the vibration to the human body. However, the effects of seat structural dynamics mode shapes and corresponding resonances have not been discussed. This study provides important knowledge about the effects of vehicle seat structural vibration modes on discomfort assessment. The occupied seat resonant frequencies and corresponding vibration modes were measured and comfort test was carried out based on the paired comparison test method. The results show that the ISO 2631-1 (1997) method significantly underestimates the vibration discomfort level around the occupied seat twisting resonant frequencies. This underestimation is mainly due to the ISO suggested location of the accelerometer pad on the seatback. The centre of the seatback is a nodal point at the seat twisting mode. Therefore, it underestimates the total vibration transferred to the occupant body from the seatback. Practitioner Summary: The effects of the vehicle seat structural dynamics have not been discussed in the human body vibration ISO . The results of this research show that the current measurement method suggested by ISO 2631-1 (1997) can significantly underestimate the vibration discomfort level at around the seat structural vibration mode.

Steady-State Vehicle Dynamics

There are two main shortcomings in existing methods for finding steering angles for the application of autodriver algorithm. First, the fact that kinematic steering angles are not accurate enough. Second, in many cases the equation of the road is so complicated that makes it impossible to solve the equations of motion of the vehicle. The proximity of the transient and steady-state responses of a sample vehicle have been checked and validated by applying a step change input to the steering angle of a vehicle traveling with constant velocity. The results are used to prove that the steady-state responses are accurate enough to replace the dynamic solutions. This concept has been used to generate a new method for finding steering angles for the application of the autodriver algorithm. The new method is named Steady-State Dynamic Steering (SSDS) and presented here for the first time. A lane change maneuver has been used to validate the results. This has been done by comparing roads resulted from using SSDS angles and kinematic steering angles. The final results show improvements in simplifying the calculation for finding steering angles which will result in shorter computation times. On the other hand, the accuracy has improved dramatically compared to the kinematic steering scenario.

Acoustical characterisation of porous sound absorbing materials: a review

Over the past 50 years, the characterisation of porous sound absorbing materials has been of increasing interest to both the acoustic engineers and customers. It is particularly important that acoustic engineers are able to predict the acoustical behaviour of these materials to get a quantitative measure of the acoustic energy absorption. This paper reviews the relevant literatures over this 50-year period and concludes that phenomenological models are currently the most accurate and suitable models of predicting the bulk acoustic properties in the whole audible frequency range. This review also presents the physical parameters which provide the link between the acoustical and material properties, as well as current experimental methods used to measure these parameters. Furthermore, the most common numerical methods for modelling porous materials are described.

A model to assess the comfort of automotive seat cushions.

A large number of independent and interacting factors affect seating comfort such as seat shape, stability, lumbar support and seat height. Although many subjective comfort studies have been conducted, few of them considered seating comfort from its subassembly level. This paper analyzed the automotive seat cushion designed with geared four-bar linkage for the seat height adjustment. The operation torque and lift distance of this mechanism was investigated as 2 major comfort factors. Ten cushions with this kind of design in the market were compared and assessed.

Better Road Design Using Clothoids

According to the mobile robot researchers and experts the best and smoothest transition curve to be used as a section of the path is the Eulers Spiral also known as Clothoid. During 19th century Arthur Talbot derived the equation of Clothoids to use as an easement curve for the purpose of avoiding the shock and disagreeable lurch of trains, due to instant change of direction. The Euler Spiral is a curve whose degree-of-curve increases directly with the distance along the curve from the start point of the spiral. This will provide a linear change in the steering angle required by the driver to go through the turn. In other word for a car which is travelling on a Clothoid transition curve of the road there will be no need for sudden changes in the steering angle of the wheels. The angle required starts from zero and increases to a maximum value and back to zero linearly. This provides a very comfortable ride for the passengers of the vehicle. The use of these curves for road design have been studied here, and a design chart have been proposed to be used for finding the best suitable transition curve for different applications.

Nonlinear Vehicle Seat BSR Characterization Using CAE Methodology

The noise and vibration of a poor automotive seat aggravate the interior cabin noise and discomfort. The automotive seat structural noise and vibration is caused by the transmission of the power train or road vibration into the seat. The characterization of seat structural dynamics behavior in early design phase assists to effectively improve the NVH quality of the seat. The seat nonlinear buzz, squeak, and rattle (BSR) noise are the major issues which are directly linked to the NVH quality of the vehicle. For this purpose, a practical CAE (computer-aided engineering) concept modeling method is introduced and developed for full BIW (body-in-white) and seat separately. Here, the seat concept model is employed to allow designing the seat structure modifications as well as examining the effects of the modifications on the rattle noise. Comparisons of the results of the simulation and experiment validate the developed seat CAE model. Three modifications are proposed to optimize the dynamics of the seat structure to prevent the seat rattle noise. These modifications are designed to shift or decrease the seat torsion resonance and vibration level, respectively. The results verified that by modification the seat structural dynamics, the nonlinear events such as rattle noise and in general BSR noise can be reduced or controlled accordingly.

Parametric Resonance: Application on Low Noise Mechanical and Electromechanical Amplifiers

Due to the growing demand for low noise signal amplification, developing mechanical and electromechanical parametric amplifiers is a topic of interest. Parametric amplification in mechanical domain refers to the method for amplifying the dynamic response of a mechanical sensor by modulating system parameters such as effective stiffness. Most of the studies in this regard have been focused on truncating equation of motion such that only linear terms remain. In this chapter, mathematical models of mechanical and electromechanical parametric amplifiers in the literature are reviewed. Then, the effect of nonlinearity is investigated by including a cubic nonlinearity on the governing equation of a classical degenerate parametric amplifier. To this end, the method of multiple scales (perturbation) has been utilized to calculate steady state solution of the nonlinear Mathieu-type equation. In addition, by determining the nature of singular points, stability analysis over the steady state response is performed. All the frequency response curves demonstrate a Duffing-like trend near the primary resonance of the system; however, the number of stable solutions changes with the parameters of the system. Furthermore, performance metrics of the system is analyzed in the presence of nonlinearity. The findings indicate that even very small nonlinearity term can dramatically decrease system performance as well as changing the relative phase in which maximum gain occurs.

Development of an acoustic material database for vehicle interior trims

Characterizing the acoustic properties of sound-absorbing materials is costly and time consuming. The acoustic material database helps the automotive designers design their interior trims in accordance with target level for interior noise. In this paper, a two-microphone impedance tube was used to measure the normal sound absorption coefficient. The main parameters that are used in the theoretical model for interior noise level assessment are investigated. These parameters include thickness, airflow resistivity, porosity, tortuosity, viscous and thermal characteristics length. The measured results have been validated by the theoretical models. The validation of normal sound absorption coefficient was found to be in agreement with its corresponding measurement data. Finally, the sensitivity of the sound absorption coefficient which is related to the physical properties mentioned above is further analyzed.

A Comparison between Caster and Lean Angle in Generating Variable Camber

A variation in the camber of an automotive wheel is desired to compensate a side-slip force change owing to normal load transfer when the car is cornering. The camber of a steered wheel can be varied by adjusting caster or lean angle which are the representations of steering axis orientation. Thus, a smart camber can be created by a variable caster or lean angle. Choosing which parameter among the two angles to be variable is very important and dependent on its different effects. Here, homogeneous transformation is employed to establish camber as a function of caster, lean angle, and steering angle in the general case. A comparison between caster and lean angle based on different criteria is then made. The comparison shows that a variable caster is much better and more feasible than a variable lean angle in generating a smart camber.