Multi Body Dynamics (MBD) simulation software is used in product development cycle to reduce the lead time to market. These software have standard parametric templates for modeling metallic suspension systems, which can be quickly modified and used in full vehicle models for ride, handling analysis and the durability load predictions. Generally every Original Equipment Manufacturer (OEM) has unique air suspension arrangement and hence standard template is not available for air suspension modeling in commercial MBD software. Air suspension with self-leveling control mechanism is preferred over metallic suspension in the commercial passenger vehicle like bus for smooth ride comfort. Hence custom made templates for these systems need to be developed for use with MBD software.
In this paper, a simplified model of air suspension is presented. Air suspension model properties are derived from the performance curves of the air bellows measured at different pressure and displacement settings obtained from physical testing. A nonlinear spline was used to model each of these load vs. displacement curves obtained at particular air spring operating pressure for the vehicle in such a way that vehicle ride height remains constant. Dynamic behavior of the air suspension was determined by the leveling valve arrangement in the vehicle, which was modeled as mechanical linkages in the model. Leveling valve operation and pressure regulation to the air spring was modeled as customized function in the Multi Body System (MBS) model.
Full vehicle bus model was created with front and rear air suspension, steering, power train and flexible bus structure. This model was used for the ride evaluation, damper sensitivity study and durability load predictions in the initial phase of the product development cycle. Simulations were performed to compare the vehicle performance with and without leveling valves to verify the design intent of the air suspension system.