Soft Switching Approach to Reducing Transition Losses in an On/Off Hydraulic Valve

Abstract

A method for significantly reducing the losses associated with an on/off controlled hydraulic system is proposed. There has been a growing interest in the use of on/off valves to control hydraulic systems as a means of improving system efficiency. While on/off valves are efficient when they are fully open or fully closed, a significant amount of energy can be lost in throttling as the valve transitions between the two states when the switching times are not negligible. A soft switching approach is proposed as a method of eliminating the majority of these transition losses. The operating principle of soft switching is that fluid can temporarily flow through a check valve or into a small chamber while valve orifices are partially closed. The fluid can then flow out of the chamber once the valve has fully transitioned. Thus, fluid flows through the valve only when it is in its most efficient fully open state. A model of the system is derived and simulated, with results indicating that the soft switching approach can reduce transition and compressibility losses by 81% and total system losses by 64%. The soft switching approach has the potential to improve the efficiency of on/ off controlled systems and is particularly beneficial as switching frequencies are increased. The soft switching approach will also facilitate the use of slower on/off valves for effective on/off control; in simulation, a valve with soft switching matched the efficiency of an on/off valve that was 4.4 times faster.

A Global Optimisation of a Switched Inertance Hydraulic System based on Genetic Algorithm

“…The 'Soft-Switching' concept is proposed to eliminate the energy losses during the switching transition [14,15]. Also, the wave propagation effect along the pipeline has been investigated in [5,16].…”

Design, Modeling, and Validation of a High-Speed Rotary Pulse-Width-Modulation On/Off Hydraulic Valve

“…The check valve circuit is potentially more efficient by reducing losses during transition in two ways: (1) limiting throttling losses to P check above P load in comparison to a fixed relief pressure which needs to be higher than any conceivable P load and (2) porting the high pressure bypassed flow to load instead of dumping the fluid to tank. The latter achieves a soft-switching function that reduces losses when the on/off valve is switching [18,19]. Figure 6 illustrates the inlet pressure profile of the VVDP over one PWM cycle along with the corresponding nozzle open area profiles to tank (solid) or to load (dotted).…”

“…(1) Equations (17) and (18) reveal that the average transition loss of the rotary valve is independent of PWM frequency. This is unlike linear valves with fixed transition time where transition losses increase with frequency.…”

Predicting solenoid valve spool displacement through current analysis

“…Switch mode control is another emerging hydraulic power modulation scheme that depends on control of a duty ratio to deliver power. This methodology requires knowledge of valve energizing and deenergizing delays and transition times to understand the actual duty ratio of the valve relative to the solenoid excitation signal duty ratio and for timing of soft switching to reduce transition losses (Rannow and Li, 2012). One approach to reduce valve delay and transition time is to apply a high voltage peak, followed by a lower holding voltage to keep the solenoid engaged and then reversing the voltage to rapidly decay the magnetic field (Breidi et al, 2014).…”