Research Article Dynamic Analysis and Design Optimization of Series Hydraulic Hybrid System through Power Bond Graph Approach R. Ramakrishnan, Somashekhar S. Hiremath, and M. Singaperumal Precision Engineering and Instrumentation Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai-600036, India Correspondence should be addressed to Somashekhar S. Hiremath; somashekhar@iitm.ac.in Received 30 September 2013; Revised 25 December 2013; Accepted 26 December 2013; Published 1 April 2014 Academic Editor: Tang-Hsien Chang Copyright © 2014 R. Ramakrishnan et al. his is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. he availability of natural gas and crude oil resources has been declining over the years. In automobile sector, the consumption of crude oil is 63% of total crude oil production in the world. Hence, automobile industries are placing more emphasis on energy eicient hydraulic hybrid systems, which can replace their conventional transmission systems. Series hydraulic hybrid system (SHHS) is a multidomain mechatronics system with two distinct power sources that includes prime mover and hydropneumatic accumulator. It replaces the conventional transmission system to drive the vehicle. he sizing of the subsystems in SHHS plays a major role in improving the energy eiciency of the vehicle. In this paper, a power bond graph approach is used to model the dynamics of the SHHS. he obtained simulation results indicate the energy low during various modes of operations. It also includes the dynamic response of hydropneumatic accumulator, prime mover, and system output speed. Further, design optimization of the system is carried out to optimize the process parameters for maximizing the system energy eiciency. his leads to increase in fuel economy and environmentally friendly vehicle. 1. Introduction he transportation sector consumes 63% of world crude oil production and causes 17% of total environmental pollution across the world. In this scenario, high cost and shortage of crude oil have created a need for energy saving, eicient, and environmental friendly transport system [1]. To mitigate this situation, a hybrid system technology was adopted to develop an energy eicient transportation vehicle. his sys- tem consists of two distinct power sources and kinetic energy recovery technology, which makes this technology a potential solution for the design of energy eicient transmission. he possible combinations of two distinct power sources are gaso- line/hydraulic (hydraulic hybrid), gasoline/electric (electric hybrid), and fuel cell/battery (fuel cell hybrid). Typically, one source converts the fuel into energy and another source is a storage unit. During mechanical friction braking in a conventional vehicle, kinetic energy in the wheel is lost as heat energy. However, hybrid system has the capability to regenerate the kinetic energy into useful energy through a method called regenerative braking. hus, the hybrid systems turn out to be a hot topic for researchers in automotive companies and research institutes all over the world [2, 3]. Generally, these systems can be classiied into two catego- ries—electric hybrids and hydraulic hybrids. he electric hybrid system is the most common and commercially avail- able hybrid system in the market such as Honda Insight, Toyota Prius, Ford Escape, and so forth. An electric battery is a major sub-subsystem in an electric hybrid vehicle, which stores the regenerated energy and delivers the same energy during acceleration of the vehicle [4, 5]. In the electric system, the round-trip eiciency for the battery is about 81%, whereas the round-trip eiciency for a hydropneumatic accumulator is 94% which has been proven by Parker Hanniin in their Cumulo systems [6]. As per the higher round-trip eiciency of the energy storage devices, the energy recovering eiciency of hydraulic system is improved to 63% when compared to 53% in electrical system. Hydropneumatic accumulator in a hydraulic hybrid possesses very high power density and quick charging capability of regenerated energy, when compared to its counterparts. herefore, this characteristic in the opera- tion of accumulator is utilized in high power requirement Hindawi Publishing Corporation International Journal of Vehicular Technology Volume 2014, Article ID 972049, 19 pages http://dx.doi.org/10.1155/2014/972049