Journal of Mechanical Science and Technology 23 (2009) 1075~1082 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-009-0344-1 Journal of Mechanical Science and Technology Sensitivity of a vehicle ride to the suspension bushing characteristics † Jorge Ambrósio * and Paulo Verissimo IDMEC-IST, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal (Manuscript Received December 24, 2008; Revised March 16, 2009; Accepted March 16, 2009) -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract The sensitivity of the ride characteristics of a road vehicle to the mechanical characteristics of the bushings used in its suspension is discussed here. First, the development and computational implementation, on a multibody dynamics environment, of a constitutive relation to model bushing elements associated with mechanical joints is presented. Bush- ings are made of a rubber type of material, which presents a nonlinear and viscoelastic relationship between the forces and moments and their corresponding displacements and rotations. Suitable bushing models for vehicle multibody models must be accurate and computationally efficient, leading to more reliable models. The bushing is modeled in a multibody code as an arrangement of springs that penalize the motion between the bodies connected. In the methodol- ogy proposed here, a finite element model of the bushing is developed in the framework of a finite element (FE) code to obtain the curves of displacement/rotation versus force/moment for different loading cases. The basic ingredients of the multibody model are the same vectors and points relations used to define kinematic constraints in any multibody formulation. Spherical, cylindrical and revolute bushing joints are developed and implemented in this work, since the methodology is demonstrated through the ride over bumps, at different speeds, of two multibody models of a road vehicle: one with perfect kinematic joints, for the suspension sub-systems; the other with bushing joints, riding. Then, sensitivities of different vehicle kinematic responses to the characteristics of the bushings used in the suspension are evaluated, by using numerical sensitivities. Based on the sensitivity analysis, indications on how to modify the vehicle response by modifying the bushing characteristics are drawn. Keywords: Elastometer models; Kinematic joint modeling; Multibody dynamics; Sensitivity analysis; Vehicle dynamics --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Road and railway vehicles must comply with a large spectrum of objectives including noise reduction, ride enhancement, dynamic behavior and/or handling improvement while reducing costs. Even after the vehicle is commercialized it may be necessary to fine- tune suspensions and other functional systems. The tools and models used in the vehicles design remain valuable for their evolution during their life. The multibody code DAP3D, based in the multi- body methodology proposed by Nikravesh [1], is used for the developments reported in this work. In this program the kinematic joints are modeled as per- fect joints, i.e., the clearance existent in real joints or the possibility of the use of deformable elements, such as bushing elements, is not taken into account. However, clearance in the joints can be easily ac- commodated as shown in the work by Flores et al.[2]. The bushing elements are important in the vehicles’ dynamic behavior because they handle misalignments between the suspension components, absorb vibra- tions and decrease the transmissibility of the road irregularities to the vehicle occupants. Their draw- back is to increase the under-steering tendency and a less responsive vehicle [3]. Elastic bushings for mul- tibody systems, consisting of linear springs to de- scribe the elastic behavior of the elastomer bushing, †This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20-23, 2008. * Corresponding author. Tel.: +351 218417680, Fax.: +351 218417915 E-mail address: jorge@dem.ist.utl.pt © KSME & Springer 2009