Thrust 1 - Efficiency

Title

1E.3: High Efficiency, High Bandwidth, Actively Controlled Variable Displacement Pump/Motor

Project Leader

Prof. John Lumkes (Purdue)

Statement of Project Goals

The goal of the project is to develop a hydraulic pump/motor that incorporates actively controlled high speed on/off valves connected to each cylinder to replace the valve plate.  The coupled dynamic model of the hydraulic pump/motor developed during this project is crucial to facilitate the development of the pump/motor.  Unit displacement is electronically controlled by on/off valve timing, not by a swash plate or other typical means. Pump/motors of this design can have increased efficiency due to reduction of friction, leakage, and compressibility losses as well as increased displacement control bandwidth (Artemis, 1990; Caterpillar, 1999; Jokela et al., 1995; Merrill, et al., 2010; Nieling et al., 2005; Reichert and Murrenhoff).  Supporting tasks include using the model to characterize and predict pump/motor efficiency, define the dynamic response and flow requirements of on/off valves required to provide significant improvements in efficiency and dynamic response over traditional pump/motors, simulate different operating strategies and characterize the effects on pump/motor efficiency (valve timing effects, partial fill methods, etc.), and to experimentally validate the model, design, and operating strategies. For experimental validation a prototype pump/motor will be built and tested.

Project's Role in Support of the Strategic Plan

The project will overcome a major system efficiency limitation in the fluid power industry by providing high bandwidth and efficient four quadrant pump/motor. This will be accomplished by providing an accurate simulation model to predict the effects of using actively controlled on/off valves to replace the valve plate timing in hydraulic pump/motors, and leveraging results from projects 1E.1 and 1E.2 on high speed valve designs. The variable displacement pump/motor will maintain high operating efficiencies at lower displacements, be capable of four quadrant operation, and exhibit high operating bandwidths. Improving pump/motor efficiency, particularly at lower displacements and throughout four quadrant operation will strengthen existing markets and enable new markets by improving efficiency and effectiveness.  A project outcome is the construction and testing of a prototype to validate the concepts developed in years one and two of the project. The project directly supports Goals 1 and 2 on the Strategic Action Maps (Improve efficiency of existing FP applications, develop 4 quadrant pump/motor and fluid powered hybrid passenger car, and increase efficiency of FP pumps and motors).

Two test beds within the center will directly benefit from the outcomes of this project. The hydraulic hybrid vehicle, where pump/motors operate in all four quadrants and at reduced displacements, will experience significant fuel economy increases with increased pump/motor efficiency. The displacement control excavator also requires high efficiency units since all power is delivered (or recovered) hydraulically using pump/motors. Also, the high bandwidth aspect of this project will help to improve the operator feedback and enable high speed motions (bucket "shaking" to dislodge material, etc.).

Description and Explanation of Research Approach

A longstanding difficulty with current state-of-the-art variable displacement pumps and motors is reduced efficiencies at partial displacements. This is the result of several factors: as displacement decreases the output power decreases, compressibility losses increase, and friction and leakage losses remain approximately constant. In addition, because in a traditional unit valve plate timing is geometrically defined as a function of shaft rotation, optimal timing is difficult to obtain over the full range of operating conditions (speed, pressure, direction, and displacement).

The challenge is to decouple the valve plate timing and provide for the ability to continuously vary the opening and closing geometries and timing as a function of real time operating conditions. Additional benefits that come with decoupling the ports include the ability to explore new operating strategies (partial fill, adaptive adjustment of noise and efficiency design tradeoffs, etc.) and increased pump/motor displacement control bandwidth.

The innovation for this project involves applying fundamental science and latest design and simulation tools to provide insight on the interacting dynamics and accompanying tradeoffs associated with independently and actively controlling the port timing for each piston in hydraulic axial or radial piston pump/motors. The project is developing fundamental insight into the design tradeoffs for actively controlled pump/motors and will provide these tools to industry. Actively controlled pump/motors as focused on in this project are more likely to be successful than past attempts because of several reasons 1) electronic and sensing capabilities have progressed significantly in the past decade, 2) new fundamental knowledge has been gained in the area of pump/motor design [Ivantysynova, 2004; Manring, 2001] and can be used in this project, 3) computational power and simulation tools are allowing for coupled multi-domain system models to be optimized, 4) the high cost of energy is making component efficiency an important consideration in operating costs, 5) previous and ongoing research on high speed on/off valves is providing the enabling technology, and 6) the CCEFP provides a unique critical mass of researchers, industry, and resources to successfully overcome the barriers.

The fundamental research barriers occur at the intersections of different physical domains represented during the short (< 1ms) transitions between high and low pressures, and the valves opening and closing. As the references make clear, the concept of actively and independently controlling the valve plate areas through the use of high speed valves is not new (Artemis, 1990; Jokela et al., 1995). What will allow the barriers to be overcome through this project is the ability to accurately model the interactions between the different physical domains and design the components to act as an optimized system capable of meeting the metrics of the project. In addition, the advanced electronics required to implement such a system have only recently become available at the processing speed, reliability, and cost levels needed. Even if the simulation and experimental results demonstrate improved performance, many practical challenges still remain. Reliability and redundancy of key components (valves and sensors) are critical when considering possible failure modes, electronics and sensors must be robust and embedded on the pump/motor to be competitive with existing units,  new packaging options should be considered since the pump/motor valves are now independently controlled and not geometrically constrained, and new system level operating strategies could be possible with "smart pumps" containing embedded microprocessors and the ability to adapt to different load requirements.

Figure 1: Efficiency comparison of actively controlled digital pump versus valve plate pump.

References

Artemis Intelligent Power LTD., "Improved Fluid-Working Machine", WPO 91/05163, 1990.

Batdorff, M., and Lumkes, J. (2009). High fidelity magnetic equivalent circuit in an axisymmetric electromagnetic actuator. IEEE Transactions on Magnetics, 45(8):3064-3072

Beachley, N. and Fronczak, F., "The 'All Hydraulic Car' - Economy and Performance Through Design Integration", Proceedings of  the 43rd National Conference on Fluid Power (NCFP), October, 1988.

Caterpillar Inc., "Hydraulically-Actuated System Having A Variable Delivery Fixed Displacement Pump", United States Patent 6216670, 1999.

Holland, M. and Lumkes, J. (2010). Test Stand Development for Investigating Digital Pump/Motor Operating Strategies. Proc. of 6th FPNI-PhD Symp. West Lafayette 2010, pp.303-314.

Ivantysynova, M., Huange, C., Christiansen, S., "Computer Aided Valve Plate Design - An Effective Way to Reduce Noise," SAE Technical Paper Series, Publication by SAE,  Warrendale, PA, USA, 2004-01-2621.

Jirrawattana, P., Fronczak, F., and Beachley, N., "Design of a Hydraulic Wheel Pump/Motor for a Hydrostatic Automobile", Proceedings of the 49th National Conference on Fluid Power (NCFP), March, 2002.

Jokela, G., Kruchowy, R., and Massey, J., "Control system for a multi-piston pump with solenoid valves for the production of constant outlet pressure flow", United States Patent 5456581, 1995.

Lumkes, J., Batdorff, M., and Mahrenholz, J. (2009). Characterization of losses in virtually variable displacement pumps. International Journal of Fluid Power, 10(3) pp. 17-27.

Mahrenholz, J. and Lumkes, J., (2009). Coupled Dynamic Model for a High Speed Pressure Balanced 3-way On/Off Hydraulic Valve. J. Dyn. Sys., Meas., Control, 132, 10p.

Manring, N. and Zhang, Y., "The Improved Volumetric-Efficiency of an Axial-Piston Pump Utilizing a Trapped-Volume Design", J Dyn Sys Meas Control 123:479-487.

Merrill, K., Holland, M. and Lumkes, J. (2010). Efficiency Analysis of a Digital Pump Motor as Compared to a Valve Plate Design. Proceedings of the 7th International Fluid Power Conference (7.IFK), Aachen, Germany, March 22-24.

Merrill, K. and Lumkes, J. (2010). Operating Strategies and Valve Requirements for Digital Pump/Motors. Proc. of 6th FPNI-PhD Symp. West Lafayette 2010, pp. 249-258

Martin, F.,"Hydraulic axial piston pump", United States Patent 5135362, 1992.

Nieling, M., Fronczak, F., and Beachley, N., "Design of a Virtually Variable Displacement Pump/Motor", Proceedings of the 50th National Conference on Fluid Power (NCFP), March, 2005.

Pettersson, M., Weddfelt, K., Palmberg, J., "Methods of Reducing Flow Ripple from Fluid Power Piston Pumps - a Theoretical Approach", SAE Technical Paper Series, Publication by SAE, Warrendale, PA, USA, 911762. pp 1-10.

Reichert, M. and Murrenhoff, H., "New Concepts and Design of High Response Hydraulic Valves using Piezo-Technology", Institute for Fluid Power Drives and Controls, RWTH Aachen University, Germany.

Wilfong, G., Batdorff, M. and Lumkes, J. (2010). Design and Dynamic Analysis of High Speed on/off Poppet Valves for Digital Pump/Motors. Proc. of 6th FPNI-PhD Symp. West Lafayette 2010, pp. 259-269.