INVESTIGTIONS OF RIDE COMFORT AND CONTROL EVALUATION OF HEAVY COMMERCIAL ROAD VEHICLE

Abstract

For developing country like India, where the demand of industry is consistently increasing from year to year, which also raises the requirement of the heavy commercial vehicle on roads for dispatching the product from one place to another. In the present scenario of India, freight road transport is the majorly used after railway freight transport. Heavy vehicle transportation is a massive enterprise with substantial direct influence on the economic growth of our country, which shares around 4.2% GDP of our nation. This rapid growth of road transportation increases traffic, and also extends the risk of accidents on roads. As per the report of the ministry of road transport, the heavy vehicle has the most impact on these accidents after two-wheelers. However, the main reason for accidents on roads is the fault of the driver. There are many reports or surveys published in a national or international level shows that whole body vibration is the reason for work-related accidents and causes many work-related diseases. A heavy vehicle like truck and buses having a large structure to carry their load, ride in all kind of terrains, for thousands of miles without failing structure. Structure (chassis or frame) of the truck must be able to sustain all kind of vibration (i.e., longitudinal, transverse and flexural). Flexural vibration was overlooked for road vehicle in literature whereas it was considered only for rail vehicles. This thesis starts with development of an analytical model with consideration of Rayleigh beam approach, where the rotary inertia of the beam is also considerd. However, very limited studies have reported for modelling a vehicle flexure vibration. This work also examines an structural damping of the chassis, which has been neglected in the past studies specifically for flexural vibration. Further, bond graph model of the flexible

vi structure of heavy road vehicle is being developed, whereas this model will be derived through modal expansion approach. A computational model of the structure consists non-linear suspension model. The dynamic response of the structure is being analyzed under various random road conditions at different vehicle speed. These random models of the road are also developed according to ISO 8608 standard, whereas four (H1-H4) kind of road category are adopted. Results are being shown the dynamic response of chassis structure under the real road responses so that parameters of the various parts of the structure has been evaluated, which further raised the ride comfort and road holding capability of the structure. Further, this work also investigates the effect of structural damping or internal damping on the dynamics of the system. This formulation is extended to build an extended formulation for flexural vibration of truck chassis through a novel approach of extended Lagrangian mechanics, where the system is asymmetric due to varying nonpotential fields of the chassis. The amplitude and the natural frequency of the vehicle frame are obtained analytically through the proposed methodology. The next focus of this work is to obtain accelerations at the driver-vehicle interface and then, to process these acceleration signals in order to calculate the human comfort. Vibration due to road irregularities constitutes another significant aspect of the physical environment after flexural vibration that can cause discomfort to the driver. Numerous approaches have been suggested and developed to access this vibration level. Thus, the comfort index calculated is independent of the seat characteristics and human parameters. Bio-dynamics of human subjects has been a topic of interest over the years, and number of mathematical models have been established. However, there are only limited studies incorporating bio-dynamic models in heavy vehicle applications. So, the

vii present work is an attempt to evaluate the ride comfort level and to calculate root mean square acceleration of different body parts as per ISO 2631 guidelines through bondgraph modeling technique. The frame flexibility is also incorporated in the model using modal expansion of a free-free beam. Physiological effects of the vibration on the human body are also analyzed using the criteria specified in International Organization for Standardization (ISO) 2631. The next significant vehicle component is the suspension system, which is generally considered as the linkage between the vehicle body and wheels. The design of a better-quality suspension system remains an essential development objective for the automotive industry. An ideal vehicle suspension should have the capability to reduce the displacement and acceleration of the vehicle body, and thus; maximizing the ride comfort. The quarter car model (two degrees of freedom) of heavy vehicle is constructed, which is being created through bondgraphs and well incorporated in semi active suspension, controlled by skyhook, ground hook and balance logic control algorithms. The 2-DOF model is subjected to road profiles like single half sine bump and random road input. This work also demonstrates various hybrid control strategies for semi-active suspension system. A new hybrid controller is proposed in this work, which consists of three "on-off" control strategies (i.e., skyhook, ground hook and balance logic). Its performance is evaluated in terms of acceleration transmissibility, and also compared with those of other proposed hybrid dampers with a new hybrid controller. The results show that the semi-active system with the proposed hybrid controller provides a better isolation at higher frequencies than previously reported hybrid controllers. Furthermore, two new proposals of hybrid robust control strategies are also studied, where PID controller is implemented along H∞ controller

viii configuration. In this configuration, first one includes single H∞ along with PID configuration, whereas the second configuration incorporates two H∞ controller along with PID arrangement. The comparative study of all these proposed controllers are being presented and the best-suited configuration for heavy vehicle system over random road condition is evaluated. The another highlight of this thesis is development of the experimental test rig of quarter car for heavy vehicle system, which is being designed and fabricated. This test rig is able to measure the performance of the heavy vehicle system in a dynamic system. The main objective to develop this test rig is to tune the suspension setting of the heavy vehicle system. The test rig also consists of MR damper, which is mounted parallel to the leaf spring arrangement. Further, the computational model of the test rig is also developed and simulation results are validated with experimental responses. The another task is to optimize the parameters for a quarter car model alongwith MR damper in a real heavy vehicle configuration. Response surface methodology (RSM) technique is profitably used in order to improve the ride comfort level of the driver.