Research On Decoupling Design Of Automotive Powertrain Mounting System In Multiple Axis Systems

Powertrain mounting system(PMS) was selected as research object. PMS is subjected to multiple excitations with constant direction and each excitation can be seen as a generalized force. A decoupling design method based on response axis was proposed to process arbitrary generalized force. Based on this method, a decoupling design method with multiple axis systems was proposed to process multiple excitations simultaneously. Screw theory was employed as a basic mathematical tool to derive decoupling design method in multiple axis systems. Effect of mount damping and frequency-dependent characteristics on decoupling design was discussed. A new design process was proposed for robust design and reliable design. Influence of PMS on vehicle system dynamics was analyzed. Each aspect of research in this article was presented as follows.First, a decoupling design method with response axis was proposed to process arbitrary generalized force with constant direction. Based on this method, a decoupling design method with multiple axis systems was proposed to process multiple excitations simultaneously. Concept of generalized force was introduced to represent arbitrary excitation, and response axis was applied to characterize response of free rigid body under a generalized force. In decoupling design, response axis is used as a reference for mode design. Mathematical basement was built in form of three theorems, and each theorem was proved. Based on concept of decoupling design with response axis, a decoupling design method with multiple axis systems was proposed to process multiple excitations acting on PMS simultaneously. Screw theory was employed to derive motion equations of rigid body in inertial axis system and body-fixed axis system. Adjacent transformation matrix was utilized for transformation between two equations. Based on motion equations of rigid body, motion equations of PMS in multiple axis systems were derived and mathematical expression of decoupling design method with multiple axis systems was presented. This method can be employed for simultaneous decoupling design of PMS under multiple excitations.Second, effect of mount damping and frequency-dependent characteristics on decoupling design method was discussed, and a method for computing natural property of PMS in Laplace domain was proposed. Effect of classical damping and un-classical damping on decoupling design was discussed and decoupling design method with response axis was proposed when considering damping of system. This method can be expressed in two equivalent forms; one is based on damping type and the other is based on system parameters. An equivalent mechanical model can be used for accurate representation of hydraulic mount. With this mechanical model, motion equation of extended PMS model was obtained and decoupling design method in multiple axis systems with damping effect was proposed. As computing method in time domain has a complicated derivation, a method for computing natural property of PMS in Laplace domain was proposed for PMS with hydraulic mount. Compared to method in time domain, the method in Laplace domain can directly use dynamic stiffness expression for computing eigenvalue and mode, and dimensions of system can keep unchanged. Meanwhile, this method can effectively represent relation between displacements of fluid element and powertrain.Third, a new design process with global algorithm and parallel computation was proposed for robust design and reliable design of PMS. Common robust and reliable design method and uncertainty analysis technique were summarized. Necessity of normal test technique was discussed in 6sigma design and a generalized 6sigma design method was proposed. Uncertainty in design of PMS was summarized. Considering uncertain factors in PMS design, based on the proposed design flow, robust design and reliable design were done for decoupling design in multiple axis systems. Results indicate necessity and advantage of robust design and reliable design was improved with uncertain level.Fourth, effect of PMS on vehicle system dynamics was discussed. For the decoupling design method with multiple axis systems, excitations from body are considered. As a rigid body with largest mass, powertrain is elastically connected to body and design of PMS have potential influence of vehicle dynamics behaviors. Based on a front axle model consisting of quarter car model and PMS, effect of PMS design on vertical dynamics behaviors was discussed. Based on a model consisting of bike model and PMS, effect of PMS design on lateral dynamics behaviors was discussed. Results indicate that natural frequency of PMS is larger than its particle frequency and natural frequency of body is smaller than its particle frequency; in order to decrease effect of PMS on body acceleration, damping of PMS can be reasonably increased and its frequency need to be apart from frequency of unsprung mass; natural yaw frequency and level of peak value increase with lateral frequency of PMS, the former contributes to extend bandwidth, but the latter can increase degree of distortion of vehicle response.