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Fuel economy is one of the major challenges for both on and off-road vehicles. Inefficient engine operation and loss of kinetic energy in the form of heat during braking are two of the major sources of wasted fuel energy. Rising energy costs, stringent emission norms and increased environmental awareness demand efficient drivetrain designs for the next generation of vehicles. This paper analyzes three different types of powertrain concepts for efficient operation of a forklift truck. Starting from a conventional torque convertor transmission, hydrostatic transmission and a hydraulic hybrid transmission (Eaton architecture) are compared for their fuel economy performance. Eaton hydraulic hybrid system is seen to perform much better compared to other two architectures. Improved fuel economy is attributed to efficient engine operation and regeneration of vehicle kinetic energy during braking.

Computer simulation is commonly used to determine the impact of hybrid vehicle technology on fuel economy and performance. One input required for this approach is a drive cycle that represents the desired vehicle speed at each time step in the simulation. Due to computational hardware limitations, simulated drive cycle durations are required to be shorter than those actually driven by real vehicles. Hence there is a need to develop a representative drive cycle of smaller time duration. For example, it is desirable to develop a one hour drive cycle that can give the same fuel economy and performance results as a drive cycle spanning many weeks. Specifically for the design of hybrid systems, it is desired that certain characteristics of micro-trips within the full length cycle are well replicated in the representative cycle. Taking these requirements into account, a new methodology was developed and tested. This paper explains this methodology and the final results obtained.

A simulation framework with a validated system model capable of estimating fuel consumption is a valuable tool in analysis and design of the hybrid vehicles. In particular, the framework can be used for (1) benchmarking the fuel economy achievable from alternate hybrid powertrain technologies, (2) investigating sensitivity of fuel savings with respect to design parameters (for example, component sizing), and (3) evaluating the performance of various supervisory control algorithms for energy management. This paper describes such a simulation framework that can be used to predict fuel economy of series hydraulic hybrid vehicle for any specified driver demand schedule (drive cycle), developed in MATLAB/Simulink. The key components of the series hydraulic hybrid vehicle are modeled using a combination of first principles and empirical data. A simplified driver model is included to follow the specified drive cycle.