The Simscape Language and Powertrain Applications

Abstract

ABSTRACT Simscape is a physical modeling language developed by Mathworks Inc. The language uses equation statements instead of assignment statements to describe physical systems. The paper focuses on the Simscape language itself instead of using components in the Simscape libraries. The language will be introduced from a perspective different from the Mathworks’ Physical Network point of view. Our perspective focuses on two types of variables at the connectors. In additional, internal variables are not separated into through and across variables. The alternative perspective is more general and easier to understand. The paper also illustrates how to develop components in a powertrain library following the proposed new perspective. INTRODUCTION Physical object-oriented modeling approach greatly facilitates model development for complex multi-domain physical systems. In this approach, models for different components are developed independently and placed into libraries. A user can select components from the libraries and connect them together just like building a physical system. Connections between component models represent actual physical connections. The model layout mimics the physical system. Therefore, the model is much easier to understand, use, and maintain. The Simscape product family from Mathworks Inc. adds the physical modeling capability to Simulink. The basic package includes a foundation library and the Simscape modeling language. The foundation library contains basic components for mechanical, electrical and hydraulic systems, etc. There are also other specialized add-on libraries. The Simscape language [1] is a modeling language used to develop custom components. The Simscape language, like most physical modeling languages [2], uses equation statements instead of assignment statements. In equation statements, input and output variables are not explicitly specified, i.e., they are non-causal. The two sides of an equation statement are equal in a mathematical sense. The equations can be either differential or algebraic. A solver sorts and solves all equations through symbolic formula manipulation. This paper will focuses on the Simscape modeling language itself instead of on developing simulation models from existing libraries. The Simscape language will be introduced from a perspective different from the Mathworks’ Physical Network point of view. The physical Network approach centers on energy flows, which is not considered in our perspective. Our perspective only focuses on two types of variables at the connectors. Internal variables are not separated into through and across variables. We think this perspective is more general and easier to understand. The paper will first discuss the basics of the Simscape language from the new perspective. We will next introduce the powertrain library that was developed with the new perspective to validate the new perspective. The paper includes component models for two-flange rotational inertia, planetary gear set, and clutch. A complete transmission model and simulation results are also included.