NORMALLY CLOSED SWITCHING VALVE FOR HIGH FREQUENCY

Transcription

1 Proceedings of 016 International Conference on Hydraulics and Pneumatics - HERVEX NORMALLY CLOSED SWITCHING VALVE FOR HIGH FREQUENCY Petrin DRUMEA 1, Radu RADOI 1, Bogdan TUDOR 1, Alexandru HRISTEA 1, Ioan BALAN 1 1 INOE IHP, ihp@fluidas.ro Abstract: Digital hydraulics appeared in the hydraulic field for a long time, without this name, but with idea on how operate still available today. One of the basics ideas is that the new devices to have a simple design and tehnology to reduce price below the level of servo valves and even of proportional directional valves. The valve presented in this article represent the normal closed type from patent aplication filed by authors. This type of valve, operated with high frequency electromagnets above 100Hz have their main role to replace the traditional servo valves which have the function principle flow control according to the current command, keeping constant a loss of pressure which in normal conditions it is up to 70 bar. Keywords: digital hydraulics, switching valve, high frequency, PWM control 1. Introduction The ellements which deffines the type of digital hydraulics [1,,3] are the distribution valves (directional valve), which in this article are on/off type, high frequency (bigger than 100 Hz). The chosen variant for analysis is the normal closed and have a functional section in fig 1. The components of interest are: Fig. 1. Normal closed switching valve - High frequency electromagnet (1) - The electromagnet shaft attached to spool () - Distribution spool (3) - Valve body (4) - Closing spring (5) - Admision chamber (0) - Crossing section (1) - Discharge chamber () While electromagnet (1) not acted (controlled) electrically, spool (3) it is pulled by spring (5) for closing the crossing area (1) [4] between the admission chamber (0) and the discharge chamber (). 9

2 Proceedings of 016 International Conference on Hydraulics and Pneumatics - HERVEX Once operated the electromagnet (1) [5] with a curent comand rectangular type appear the oppening of crossing areea (1) noted in the graffic from Fig. with A max. Along with the increasing frequency of closing-opening of the area (therefore the electromagnet working frequency). The efective area of passage become A t taking the shape from area c) of the figure.. Mathematical models Fig. Effective passage area through valve.1. Determination of the pass debit Q from the admission chamber (0) in the discharge chamber () by the crossing chamber (1). Elements of flowing section are shown in Fig. 3 Q = C D S C ρ Δp (1) S C =π d n e=π e d +d 3 d m = d +d 3 e = y c sin α d +d 3 = e cos α = y c sin α cosα d 3 =d - y c sin α cosα d 3 = d - y c sin α () (3) (4) (5) (6) (7) In the end, S C = π d n y c sin α = π y c sin α d +d 3 S C = π y c sin α d +d ysinα = π y c sin α d 1 y sinα d (8) how y c <<d and y c sinα<<d S c π d y c sin α (9) And replacing (9) in (1) to obtain: 93

3 Proceedings of 016 International Conference on Hydraulics and Pneumatics - HERVEX Q = C D π d y c sin α Δp ρ (10) Q = C D π d y c sin α ρ p 1 p (11) Fig. 3 Flowing section. Conservation equation of flow from entering the valve Q = Q p - Q t - ΔQ e (1) Q = the flow goes to user Q p the flow delivered by the pump ΔQ e compressibility flow asociated with the volume valve hydraulic motor.3. The equation of dynamic equilibrium of the command spool F em = F s +F i +F f +F h (13) F em electromagnet force F s spring force F i inertial viscous force F f force of viscous friction F h hydrodynamic force in transient regim F em =k e i c -k s y c (14) with: k e and k s constants i c command current y c movement of the spool and the mobile core F pc = π + d 4 1 p (15) F pc - pressure force against the command spool d 1 spool diameter p adjusted pressure F s = k s (x o +y c ) (16) k s constant of the spool spring 94

4 Proceedings of 016 International Conference on Hydraulics and Pneumatics - HERVEX x o spool spring pre-grip F hs hydrodinamic force F hs = c d π d s y c sinα(p 1 -p ) cosθ c v (17) Fν - force of viscous friction Fν= π d l s μ dx j s dt F i inertial force F i =m p d x dt F h f - transient hydrodynamic force component F h f = π c d d 1 l ts P y c dp 1 p 1 dt 3. Simulating mathematical models The simulation is on a Mathlab/Simulink platform. Starting with the mathematical models determinated at the point and having the next parameters: (18) (19) (0) d 1 = 8 14 mm d = d 1 -( 4) mm y c = 0,1 0,8 mm spool stroke C D = 0,6 and 0,65 flow coefficient p 1 = max 00*10 5 N/m p = max 00*10 5 N/m p 1 -p = max 00*10 5 N/m ρ s = 7850 kg/m 3 - the density of the spool material ρ f = 860 kg/m 3 - the density of the working fluid α 45; 60; 75 and 90 degrees k s = 45 N/mm spool const. C v = 0, 0,8 speed coefficient = 0,03 kg/m*s dynamic viscosity = 69 j = 0,1 mm Fig. 4. Simulation diagram for valve flow 95

5 Proceedings of 016 International Conference on Hydraulics and Pneumatics - HERVEX Fig. 5. Simulations results for valve flow at different valve angle Fig. 6. Simulation diagram for hydrodynamic force 96

6 Proceedings of 016 International Conference on Hydraulics and Pneumatics - HERVEX Fig. 7. Simulations results for hydrodynamic force Fig. 8. Simulation diagram for viscous force Fig. 9. Simulations results for viscous force 4. Conclusions Hydraulic switching is a subdomain of digital hydraulics, which is characterized by achieving control only just using discrete states. In switching hydraulics these components with discrete states are commutations valves. Digital valves for switching hydraulics have simple design and low cost. Their command require a special electronic module which provide PWM signal. This equipment have better energy efficiency compared to conventional servo and proportional valves. References [1] R. Scheidl, H. Kogler, B. Winkler, Hydraulic switching control objectives, concepts, challenges and potential applications,hervex 01, Calimanesti-Caciulata, Romania, 7-9 November, Proc. ISSN , pp.56-67; [] B. Winkler, A. Plockinger, R. Scheidl, Components for digital and switching hydraulics, The First Workshop on Digital Fluid Power, 3 rd October, 008, Tampere, Finland; [3] A. Plockinger, R. Scheidl, B. Winkler, Fast Development and Rapid Prototyping of a Compact Fast 3/ Way Switching Valve, Proc. Int. Conference on Hydraulics and Pneumatics, ISBN , pp , 008, Prag, Czech Republic; [4] I. Sfarlea, L. Marcu, D. Banyai, Flow through command hydraulic resistance, Hidraulica Magazine no. 3 /015 ISSN , pp.59-64; [5] G. Matache, P. Drumea, M. Comes, I. Ilie, Echipament proportional de reglare a presiunii, Hidraulica Magazine no. 1 /005 ISSN , pp