Analogue and Digital Modelling in the Design of a Hydraulic Vehicular Transmission

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Abstract
This paper is concerned with the design and development of a hydraulic hybrid urban vehicle power plant using a small internal combustion engine prime mover, a hydraulic transmission, and a hydraulic accumulator as a small energy store. The driver controls the vehicle velocity by operating the swashplate of the axial-piston variable-displacement hydraulic motor. The remaining system inputs, i.e., the engine throttle and swashplate of the axial-piston variable-displacement hydraulic pump, are governed by a multiloop electronic controller via electro-hydraulic servo-actuators. The system aims to achieve a high overall efficiency by utilizing the hydraulic accumulator to maintain optimal loading of the prime mover and to provide regenerative braking. The design was aided by an analogue simulation implemented on an EAI 690 hybrid computer. For the final quantitative evaluation of the system, a digital simulation program was written using the MIMIC processor. Realistic modelling was attained in both cases by using manufacturers' data for commercially available components to define the dynamic response and efficiency of the individual elements of the overall system. The simulation model was subjected to accelerator/decelerator step input signals under various road conditions. ‘Drives’ through the standard LA-4 and EPA standard urban cycles were performed. The simulation results showed high system stability, satisfactory acceleration and deceleration performance and a good overall efficiency.

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