Investigation of factors affecting steering effort in heavy commercial vehicles

Hydraulic power steering system which is also called as power assistance is used through long ages to reduce steering effort that happen due to design of steering system and suspension system. Steering system efficiency has been increased while breakthrough design and new technology products has been added to this system. By developing electronic technology, electro-hydraulic power steering system (EHPAS) has been used after electric motor was added to hydraulic power steering system instead of internal combustion engine. Nowadays, Electric power steering system (EPAS) is used to reduce steering effort and increasing driving comfort and maneuverability and also perform the active safety system. Low steering effort is a necessity for driver to increase driving comfort and easy maneuverability on turns. Several component in the suspension and steering system play a key role in determining the steering effort of vehicle. Long-distance drivers or drivers who drive heavy commercial vehicles on challenging construction and mine sites to maneuver hardly on turns at the uneven and narrow road, want that vehicles have low steering effort. There are many factors which cause the steering effort. Some of the most effective factors for steering effort are listed below. •Steering gear relief valve pressure adjustment •Steering wheel diameter •Wheelbase and various of linkage design •Recirculating ball type steering gear •Auxiliary hydraulic cylinder In this study, 8x4 command steer vehicle was used to examine above mentioned factors on vehicle. As it can be seen from literature survey, overloading causes the high steering effort. Gross vehicle mass for 8x4 command steer vehicle is higher than others, that's why this vehicle was chosen for vehicle test. Five different methods have been identified to determine the parameters affecting steering effort. Firstly, the effect of steering gears which was fixed in different relief valve pressure value has been examined. Data was collected by using torque-angle sensor to analyse values. The collected data was analysed using DEWEsoft program. The effect of the different diameter of steering wheel to steering effort was evaluated. In the second comparison, the effect of steering wheels which have different diameters to steering effort was examined. In the third comparison, different steering linkages is designed in order to provide the suitable packaging at the vehicles which have different wheelbase. Effect of the different linkage design to steering effort was examined. In the fourth comparison, recirculating ball type steering gears which have different technical feature was evaluated. Lastly, three hydraulic cylinder with different technical features and two pitman arm with different designs were used and the torque which was made by combinations formed between them was analysed. Catia program was used during pitman arm design. Loads impact on steering system due to different forces provided by hydraulic cylinders have been investigated using Abaqus program. CAE analysis for newly designed pitman arm was carried out. The above steps were followed sequentially and in detail and the effects of the factors on the steering effort were determined. The obtained data shed some light on criteria that must be selected to be decreased steering high effort in newly designed steering system.