Control and energy performances of water hydraulic FST and PMT systems

Water hydraulics is increasingly used in industrial application because of its inherent advantages including environmental friendliness, high safety against fire hazards, running cost reduction, and easy availability. However, water hydraulics remains two restrictions to make it popular in real application; higher price of water hydraulic devices and larger energy loss than conventional one. Thus, finding a suitable water hydraulic system that can reduce the price and save energy is one of the most important requirements for water hydraulic society. A water hydraulic fluid switching transmission (FST) and a water hydraulic pump motor transmission (PMT) that use cheap devices and can recover energy in deceleration process are good solutions for these difficulties. This study aims to compare two most important performances that are velocity response and energy saving of water hydraulic FST and PMT systems, in particular, focusing on detail analysis of energy saving performance. A method to estimate the relative wasted energy of FST in comparison with PMT system is also proposed. The PMT system has revealed many advantages such as reducing noise because of smooth operation, lengthening the duration of life of the devices, and especially the drastic reduction in both steady state errors in working phase and energy consumption