Analysis of velocity control performance and energy recovery efficiency of water hydraulic fluid switching transmission

Beside various fluid power transmissions, a new water hydraulic Fluid Switching Transmission (FST) has demonstrated outstanding advantages such as environmental friendliness, safety, running cost reduction, and lower energy loss for using only ON/OFF valves. Especially, this system has no servo or proportional valve; thus, lower power transmission loss can be expected. In this paper, two most important aspects of the FST system, velocity control and energy saving performances, will be presented. First, the error of the load rotational velocity is mainly influenced by property of ON/OFF valves, velocity transducer, and control logic. The research solved the problem - how to reduce the percentage error of velocity control. The experimental results showed that the error could be reduced to less than 3% for all given reference speeds equal or above 800 revolutions per minute (min^-1). Second, the system regenerated the kinetic energy of the load by storing it into an accumulator during deceleration phase. This energy will be reused as the second driving source in the next cycle. By this way, 26- 36% of the kinetic energy can be saved corresponding with the reference velocities. Furthermore, to reduce energy consumption, a method to control electric motor was also proposed and shown that the energy consumption reduced drastically - more than 50%.