Thrust 1 - Efficiency
Title
1E.1: Helical Ring On/Off Valve-Based 4-Quadrant Virtually Variable Displacement Pump/Motor
Project Leader
Prof. Perry Li (UMN)
Statement of Project Goals
The goal of the project is to demonstrate high performance, efficient control of hydraulic power using on/off valves in a throttle-less manner. This goal will be met through the development of critical enabling technologies such as novel high speed rotary on/off valves that will be integrated into virtually variable displacement pump/motors (VVDPM) for demonstration on CCEFP test beds. In addition to the rotary spool valve approach studied in previous years, a newly proposed rotary valve based on a ring control element will be developed. This new ring valve has been conceived with the objective of improving valve efficiency at high pressure and high bandwidth operation by simplifying the valve flow path while simultaneously reducing the internal compressible volume. Prototype targets include 21-35MPa operating pressure, VVDPM system bandwidth in excess of 10Hz, and hydraulic valve efficiency greater than 85% at 50% VVDPM displacement.
Project Role in Support of Strategic Plan
This project addresses the efficient component/operation barrier by enabling throttle-less control approaches that replace the use of inefficient throttling valves. It also addresses the compactness barrier by enabling variable displacement functionality using compact, inexpensive fixed displacement components. Pulse-width-modulation (PWM) of hydraulic power using on/off valves is a potentially efficient control concept that is analogous to switched mode converters used in power electronics [1]. By pairing on/off valves with a fixed displacement pump or motor of any type, variable displacement functionality can be achieved with designs that are inherently efficient or compact but traditionally fixed.
Description and Explanation of Research Approach
Current methods of controlling fluid power systems are either inefficient (throttling valve control) or expensive and bulky (mechanical variable displacement pump or piston-by-piston digital pump). The virtually variable displacement pump/motors (VVDPM) proposed in this project combine the strengths of traditional approaches by enabling throttle-less displacement control of compact, inexpensive fixed displacement pump/motors using a single on/off valve. One such VVDPM implementation based on a 4-way tandem on/off valve is shown in Fig. 1.
Figure 1: Hydraulic schematic of a VVDPM using a 4-way tandem rotary on/off valve
The lack of high-speed on/off valves, which are the counterparts to electronic transistors, is a major challenge. These on/off valves must have large orifices to allow high flow at low pressure drop. They must have fast transitions to reduce the time when the valve is partially open. And, they must have the ability to operate at high PWM frequencies to reduce ripple and achieve high control bandwidth. A typical control valve consists of a linear translating element such as a spool or poppet. The element must be accelerated and decelerated rapidly to be used in PWM control. This requires large actuators, since power input is proportional to the cube of the PWM frequency. Our approach is to develop novel rotary PWM on/off valves that use continuous rotary motion to generate on/off switching. These rotary valves do not need to start and stop; therefore, the only power required is that to overcome friction, which is proportional to frequency squared. Moreover, in applications where the pump or motor shaft speed is fixed (i.e. constant flow rate through the valve), the rotary actuation power can be obtained by scavenging energy in the fluid stream without using an external actuator. The average response time and effective flow area for several commercial on/off valves and a few valves found in the literature [2, 3] are compared to the prototype rotary valve in Fig. 2.
Figure 2: Effective flow area and response times of existing on/off valves
References
[1] Li, P., Li, C., Chase, T., 2005. "Software enabled variable displacement pumps". Proceedings of the ASME IMECE '05 #81376, Orlando, FL.
[2] Yokota, S., and Akutu, K., 1991. "A fast-acting electro-hydraulic digital transducer (a poppet-type on-off valve using a multilayered piezoelectric device)". JSME International Journal.
[3] Cui, P., Burton, R., and Ukrainetz, P., 1991. "Development of a high speed on/off valve". Transactions of the SAE.
[4] Tu, H., Rannow, M., Van de Ven, J., Wang, M., Li, P., and Chase, T., "High speed rotary pulse width modulated on/off valve", Proceedings of the ASME IMECE '07 #42559, Seattle, WA.
[5] Yu, J., Chen, Z., and Lu, Y., 1994. "The variation of oil effective bulk modulus with pressure in hydraulic systems". Journal of Dynamic Systems Measurement and Control.
[6] Tu, H., Rannow, M., Wang, M., Li, P., and Chase, T., "Modeling and validation of a high speed rotary PWM on/off valve", Proceedings of the ASME 2009 DSCC #2763, Hollywood, CA.
[7] Rannow, M., and Li, P., "Soft switching approach to reducing transition losses in an on/off hydraulic valve", Proceedings of the ASME 2009 DSCC #2617, Hollywood, CA.
[8] Rannow, M., Li, P., Chase, T., Tu, H., and Wang, M., 2010. "Optimal design of a high-speed on/off valve for a hydraulic hybrid vehicle application". Proceedings of the 7th International Fluid Power Conference, Aachen, Germany.
[9] Wang, M., and Li, P., "Duty ratio control of a rotary PWM valve with periodic measurement error", Proceedings of the 2009 American Control Conference, St. Louis, MO.
[10] M. Wang, and P. Y. Li, "Event Based Kalman Filter Observer For Rotary High Speed On/Off Valve", Proceedings of the 2008 American Control Conference, pp 1546-1551, June, 2008.
[11] M. B. Rannow and P. Y. Li, "On/Off Valve Based Position Control of a Hydraulic Cylinder", Proceedings of the ASME IMECE '07 #42590, Seattle, WA.
[12] M. Rannow, H. Tu, P.Y. Li and T.R. Chase, "Software Enabled Variable Displacement Pumps - Experimental Studies," Proceedings of the ASME IMECE '06 #14973, Chicago, IL.