DIGITAL HYDRAULICS SOLUTIONS

Transcription

1 DIGITAL HYDRAULICS SOLUTIONS Petrin DRUMEA 1, Radu RĂDOI 2, Bogdan TUDOR 3, Ilare BORDEAȘU 4 1 INOE IHP, ihp@fluidas.ro 2 radoi.ihp@fluidas.ro 3 btudor.ihp@fluidas.ro 4 Polytechnic University of Timisoara, ilarica59@gmail.com Abstract: The material presents the most important solutions used in digital hydraulics and two solutions of digital hydraulic distributor constructed by the authors. Keywords:digital hydraulic, solutions, distributor 1. Introduction Hydraulic actuation with its tradition starting from antiquity begun to lose ground in front of another type of actuation, such as pneumatic and electrical actuation, mainly due to intensive energy losses which hundreds of years did not matter. It should be mentioned that for a long period the most important thing for machinery and complex line was that hydraulics to make necessary movements in the time required, and the energy consumption does not matter in huge costs of the complex systems in general. The problems of reducing energy consumption have appeared in recent years, precisely at the same time with the developing of the hydraulics actuation of the mobile machinery. Of course that the installing, maintenance, to reduce the CO2 emissions issues created a state of anxiety in the field. The immediate reaction consisted in upgrade of the equipment by improving fields, adapting hydraulic components for the new computerized drive scheme and automation for obtaining consumptions at the requested level from the mechanical drive systems and lately to recovery a fraction of the lost energy and the emergence of digital hydraulics. [1] 2. The concept of digital hydraulics Great novelty of the 90s was the transfer of digital hydraulics from theory to practice. This thing was manageable due to specialists such as Scheidl, Linjama, Vilenius, Bishop, Wadsley, Merrill, Kudzma, Ploeckinger, etc., who had the first notable practice results.[2],[3] 2.1. The definition of digital hydraulics Digital Fluid Power means hydraulic and pneumatic systems having discrete valued component(s) actively controlling system output (4). Very important for digital hydraulics is the intelligent control. In Europe there is accepted that digital hydraulics has a branch that was based on parallel connections, with a strong centre located in Tampere, and a branch based on the switching technology, with a strong centre in Linz. It should be specified that digital hydraulics does not mean traditional hydraulics, classic or modern with analog element which we drive with digital electronics. Digital hydraulics means hydraulics or pneumatics systems which have in their structure at least one hydraulic element to ensure at the exit specifically discrete values and active control. This thing involves beside the digital hydraulic elements a proper electronic command, so a good computerization of the system. 73

2 2.2. The advantages of digital hydraulics The advantages of digital hydraulics are extremely clear at the theoretical level, but less visible in industrial practice. The hopes related to speed, robustness, simplicity and equipment reliability is not yet materialized in industrial products used on the large scale or in some specific areas. Comparative with the standard on/off hydraulics, digital hydraulics has a response time much smaller, but it keeps the durability and work capacity in dirty mediums of the classic hydraulics drives. Specialists from Tampere estimate that there is the possibility to save a percentage of fuel between 20 and 40%, machines becoming more simple and light-weight without a price rising. Digitization of all mobile machines can reduce consumption on road with a percentage between 5 and 10%. Even the general architecture of the hydraulically operated vehicle can be simplified by using digital hydraulics, as in figures 1 and 2, as indicated by L. Wadsley.[4] Fig. 1. Typical mobile machine layout [4] Fig. 2. Alternative mobile machine layout [4] 3. Solutions of digital hydraulic pumps and motors solutions 3.1. The digital hydraulic pump and motor are, as the Luke Wadsley from the company Sauer Danfoss states, related to the construction methods of the displacement and how the cylinder with the piston goes from suction to discharge. The simplified scheme in fig. 3 represents the basic functional element, which actually is equivalent with the classic pump having inline pistons which is done electronic both the commutation from suction to discharge and the displacement adjustment.[4] Fig. 3. Digital pump element [4] Very interesting are those digital pumps and hydraulic motors produced by the company ARTEMIS, which are controlled directly with quick directional valves controlled with microprocessors. A schematic presentation of the pump and motors used in digital hydraulic systems with parallel distributions and those used in switching technologies, are found in the work of professor Lindjama and they are presented in figures 4, 5, 6.[5] 74

3 Fig. 4. Switching pump (a) and parallel connected pumps (b) [5] Fig. 5. Piston type digital pump (a) and pump-motor (b) [5] 3.2. Digital hydraulic cylinders Fig. 6. Switching motor (b) and parallel connected motors (b) [5] In time there has appeared the theoretical idea that says the yield of an installation where the working pressure varies with the load it is worse than of a system where working pressure is constant and it is variable the area of cylinder piston. The one who has had the first serious concerns in this field was the American Elton Bishop, who invented in 2001 the digital hydraulic transformer (DHT). In figures 7 and 8 it becomes clear what digitalization of cylinders meant. [6] 75

4 Fig. 7. [6] Fig. 8. [6] Figure 9 presents few of the possible options for the linear actuator with variable displacement (VDLA), and figure 10 is a schematic diagram presenting the digital hydraulic transformer (DHT). Fig. 9. [6] Fig. 10. [6] An interesting synthesis is made by professor Scheidl from a paper of the professor Linjama, and presented in this material in figure 11.[7] 76

5 4. Digital hydraulics with parallel distribution Fig. 11. [7] The history of hydraulics with parallel distribution it is quite long, probable starting with the year 1883 when was constructed the water pump station in London, continuing with Rickenberg, Murphy si Weil. Even the work of Virvalo from the 70 s failed to introduce the idea of digital hydraulics. Only started with the collective works from Tampere, which they defined the digital flow control unit (DFCU), presented in figure 12, in a two-way version, and in figure 13 in a four-way version. Fig. 12. [5] Fig. 13. [5] 5. Digital hydraulics switching technology The mechatronics centre from Linz assumed some ideas of the electric drive technology by switch command and was placed the basics of commutation the digital hydraulics, with the base the analogy of the electric switching systems with the hydraulic ones, as one can see in figure

6 Fig. 14. [7] Figure 15 shows schematically the hydraulic directional valve switching solution, developed at the University of Linz. Fig. 15. [7] Figure 16 shows a summary table of the switching methods (2). Fig. 16. [7] 78

7 In hydraulic installation of metal production machinery, agriculture machinery, machine tools will surely use this type of digital hydraulics, but after completing the range of items with fast check valves, with high performance pneumo-hydraulic accumulators. 6. Conclusions In Romania, there are few researches in the field of digital hydraulics, and the great achievements are fewer. The only theoretical attempts and achievement of some components are those of the research group within INOE 2000 IHP, which developed a hydraulic directional valve found at the stage of functional model, for which a patent application (no A/00432/2016) has been elaborated and submitted to the Romanian State Office for Inventions and Trademarks (OSIM) [8]. A small group led by the professor I. Bordeiasu from the Technical University Traian Vuia of Timisoara and another group led by professors Vaida and Opruta from the Technical University of Cluj-Napoca have joined the aforementioned research group. The version addressed by the specialists from IHP Bucharest is that of switching digital hydraulics, represented on international level by professor Scheidl from the University of Leinz, Austria. The group of specialists from IHP, led by PhD. eng. Petrin Drumea, have PhD. eng. M. Blejan and PhD. eng. R. Radoi, dipl. eng. Al. Hristea and dipl. eng. B. Tudor as leading researchers, and they focused on building two types of directional valves, which are represented below (Fig. 17). References a. Normally closed type b. Normally open type Fig. 17. [1] H. Theissen Fluid Power For Sustainability, Proc. of 20th International Conference of Hydraulics, Pneumatics, Sealing Elements, Fine Mechanics, Tools, Specific Electronic Equipment & Mechatronics HERVEX 2012, November 7-9, Calimanesti-Caciulata, Romania, ISSN , pp ; [2] R. Scheidl, H. Kogler, Hydraulic Switching Control - State of the Art and Challenges, 2012; [3] A. Plöckinger, B. Winkler, R. Scheidl, Development and Prototyping of a Compact, Fast 3/2 Way Switching Valve with Integrated Onboard Electronics,The 11 th Scandinavian International Conference of Fluid Power, SICFP 09, June 2-4, 2009, Linkőping, Sweden, ISBN , pp ; [4] L. Wadsley, Optimal System Solutions Enabled by Digital Pumps, The 52 nd National Conference on Fluid Power, March 23-25, 2011, Las Vegas, pp.7-13; [5] M. Linjama, Digital Fluid Power-State of Art, The 12 th Scandinavian International Conference of Fluid Power, May 18-20, 2011, Tampere, Finland, ISBN ; [6] E. Bishop, Digital Hydraulics, [7] R. Scheidl, H. Kogler, B. Winkler, Hydraulic Switching Control-Objectives, Concepts, Challenges and Potential Applications, Proc. of 20th International Conference of Hydraulics, Pneumatics, Sealing Elements, Fine Mechanics, Tools, Specific Electronic Equipment & Mechatronics HERVEX 2012, November 7-9, ISSN ; [8] Patent application no. A/00432/2016, Hydraulic distributor with electric command, switching, high frequency and low flows. 79