In commercial vehicles, leaf springs play a major role in designing the suspension system. Leaf springs are the most popular designs having multiple leaves in contact with each other and show hysteresis behavior when loaded and unloaded. The leaf spring acts as a linkage for holding the axle in position and thus separate linkages are not necessary. It makes the construction of the suspension simple and strong. Because the positioning of the axle is carried out by the leaf springs, it is disadvantageous to use soft springs i.e. springs with low spring constant. Leaf springs are excellent in suspending large loads, since they are designed using 'bending beam' equations. The stiffness of the leaf spring assembly can be altered as desired, by changing the number of leaves. The objective of this paper is to compare the bending loads coming at the rear wheel centers of the vehicle when it runs in torture track and over a single bump. Bending loads were compared for the same rear suspension but two different leaf springs (7 leaf suspension system and 11 leaf suspension system). Comparative study of bending loads coming at wheel centers of heavy commercial vehicles for the same rear suspension system connected with two different leaf springs has been discussed in this paper. The change in loads expected on the rear axles have been evaluated using appropriate strain gauging on the rear axles. Due to the increase in the stiffness of the spring, the 11 leaf suspension is giving better performance as compared to the 7 leaf suspension in most of the terrains like Twist, Pebbles, Potholes and Corrugated tracks . To get the better understanding of the quasi static loads on the suspension, the vehicle ran over a single bump and proved that the better performance is observed in the 11 leaf suspension. Keywords: Suspension, Leaf spring, Bending loads, Torture Track, Single bump, Wheel center, Calibration, Strain gauge, Data acquisition, Sample rate, Gross Vehicle Weight (GVW).

Mr. RAJESH KORRAYI, Sr.Manager, Tata Motors Limited