SIMULATION MODEL OF PNEUMATIC
Transkrypt
SIMULATION MODEL OF PNEUMATIC
PROCEEDINGS OF THE INSTITUTE OF VEHICLES 3(107)/2016 Piotr Mróz1, Sebastian Brol2 SIMULATION MODEL OF PNEUMATIC-HYDRAULIC DRIVE 1. Introduction The accumulation of energies is very important today. Gathering and storage of heat from solar radiation examined since the early XIX century. Now is known that the accumulated amount of heat depends heavily on participation of gas in Earth's atmosphere [1]. Theorizes the impact human activity has on emissivity the so-called greenhouse gases. It is estimated that about 20% of greenhouse gas emissions are emissions from road transport [2]. Vehicle manufacturers through legal restrictions of emissions (f. e. Euro standards, standards CO2), are obliged to implement technical solutions that contribute to fewer and fewer greenhouse gases emissions by their vehicles. These solutions are mainly: start / stop system, diesel - particulate filters, reactors for the chemical processing of exhaust gases, alternative fuel, alternative drive, hybrid systems (plug-in systems). Based on the literature, it was observed a trend in development of hydraulic hybrid vehicles. These are vehicles in which the mechanical drive system is assisted by hydraulic system (parallel hybrid - PHHV) or a mechanical system for the most part replaced the hydraulic system (serial hybrid - SHHV). Table 1. shows the strengths and weaknesses hydraulic hybrid vehicles (HHV) on the background of the more popular and more studied hybrid electric vehicles (HEV). Table 1. Advantages and disadvantages of hydraulic hybrid vehicle ADVANTAGES Better fuel economy than HEV (in some cases) Lower life cost than HHV Lower accumulator degradation Lower investment cost DISADVANTAGES Lower energy density in accumulators than in other solutions Lower range on hydraulic drive itself Excessive power waist collected in braking Higher CO2 emission compared to PHEV or EV Hydraulic hybrid vehicles use energy stored in hydraulic accumulators. It was estimated that they collect less energy than electric batteries, but have a high power density [3]. In addition, an attempt to estimate the cost-effectiveness of reducing CO2 emissions through the introduction of a variety of hybrid technology [4]. Estimates show that to reduce emissions can the most contribute hybrid plug-in. These solutions, where it is possible to recharge energy for hybrid hydraulic replacement tank of compressed gas on a fully charged or refueled the tank, as currently is the case for combustion 1 2 mgr inż. Piotr Mróz, doctoral student of Opole University of Technology, dr hab. inż. Sebastian Brol, Opole University of Technology Professor, Department of Road and Agricultural Vehicles, [email protected] 45 vehicles. Such solutions are now largely unexamined, but it is estimated that they can bring the most cost-savings [5]. High impact on the profitability of the development of the hydraulic hybrid is only a sort of hybrid. For comparison (Fig. 1.), the parallel hybrid electric and hydraulic bring savings on a similar level. While the SHHV brings approx. 20% more savings than SHEV. Fig. 1. Precentage improovement in economic savings [5] where: CONV – conventional vehicle, SHEV – series hybrid electric vehicle, SHHV – series hybrid hydraulic vehicle, PHEV – parallel hybrid electric vehicle, PHHV – parallel hybrid hydraulic vehicle, EV – electric vehicle, HEHV – hybrid electric hydraulic vehicle. Known solutions of hydraulic hybrid vehicles usually use an internal combustion engine as a generator of high pressure (series hybrid) or can work independently (parallel hybrid), where the hydraulic system supports their work, eg. when climbing or acceleration of the vehicle. On the development of technology of hydraulic hybrid vehicles work many companies (including Eaton, Bosch-Rexroth). At the present moment it was not found any deployed passenger vehicle that use a hydraulic hybrid technology. Many vehicle prototypes are available for testing for the media and presented at the motor shows. And over from 2007 - 2016 was observed increase in the number of scientific papers about the hydraulic hybrid vehicles. Hydraulic hybrid vehicles have a relatively low range on hydraulic drive, which is due to the low volume (20 - 40 dm3) of hydraulic accumulators. Fully discharge an accumulator is after 300-1000 meters of driving. Distance could be increased if it were possible to use an unlimited amount of hydraulic fluid. 2. Pneumatic-hydraulic drive Based on the literature a solution was found that could significantly improve the range of hydraulic hybrid vehicles. Figure 2. shows a the pneumatic-hydraulic drive unit. 46 Fig. 2. Pneumatic-hydraulic power unit according to Shaw [6] where: AT - air tank, DPV - directional pneumatic valve, AOC - air-oil energy converter, DHV - directional hydraulic valve, HM - hydraulic motor. This concept allows pumping hydraulic fluid by compressed gas from one accumulator to another and to move the hydraulic motor. In such a system, the hydraulic motor can work independently without the participation of the internal combustion engine. In carrying out the cycles of pumping, it is possible to an unlimited number of pumping hydraulic fluid at a limited number of compressed gas, the amount of which can significantly increase the range of the vehicle compared to the known solutions are hydraulic hybrid vehicles. There is not known by authors any paper, where Shaw would develop his solution for the vehicle, so an attempt to build a similar, modified pneumatic-hydraulic drive unit. ATV-type vehicle equipped with a prototype of the pneumo-hydraulic drive unit, and in table 2. below summarizes the most important parameters before and after the modification of the drive system. Table 2. Features of vehicle before and after modification Features of vehicle before modification GVW 360 kg Engine capacity 149 cm3 Max. power 7,1 kW (7000 rpm) Max. torque 10 Nm (6000 rpm) Type of gear automatic Max. velocity 65 kph Drag forces (total) Features of pneumatic-hydraulic drive Tank capacity 44 000 cm3(30 MPa) Gas Nitrogen Accu. capacity 2000 cm3 (2 pcs.) Max. torque 41 Nm (@15 MPa) Gear 2 stage Max. velocity 45 kph 50 N - 180 N At the present moment, the most important modification of the Shaw’s basic system, include specially paired hydraulic valves, which enables the system to maintain a constant direction of rotation of the hydraulic motor, regardless of the direction of flow of hydraulic fluid between hydraulic accumulators. 3. Simulation model During an earlier work [7] simulation model in MatLAB Simulink environment (Fig. 3.) was prepared, 47 Fig. 3. Scheme of simulation model of pneumatic-hydraulic drive where: T – air tank, A – pneumatic-hydraulic accumulator, LV - loading valve, DV – drain valve mT0 – initial mass of gas in tank, mA0 – initial mass of gas in accumulator, TT0 – initial temperature of gas in tank, T A0 – initial temperature of gas in accumulator, pT0 – initial pressure of gas in tank, p A0 – initial pressure of gas in accumulator, p AP – preset pressure of gas in accumulator, mT – mass of gas in tank, T – mass flow rate of gas in tank, TT – temperature of gas in tank, T – temperature flow rate of gas in tank, pT –pressure of gas in tank, VT – volume of gas in tank, mA – mass of gas in accumulator, A – mass flow rate of gas in accumulator, T A – temperature of gas in accumulator, A – temperature flow rate of gas in accumulator, pA –pressure of gas in accumulator, V A – volume of gas in accumulator, TA – mass flow rate of gas between tank and accumulator, TTA – temperature of gas between tank and accumulator. The modeled gas process was adiabatic expansion of nitrogen from the tank to the gas side of pneumatic-hydraulic accumulator. It was assumed that T = TA = A, because pipe and valve connecting tank and accumulator, is not modeled. For simulation it was also assumed a constant parameters and variables range, which shown in table 3. Table 3. Significant constant and variable parameters of the simulation model Parameter Molar mass of nitrogen Initial mass of gas in tank Initial mass of gas in accumulator Initial temperature of gas in tank, Initial temperature of gas in accumulator, Initial pressure of gas in tank, Initial pressure of gas in accumulator, Preset pressure of gas in accumulator Volume of gas in tank Volume of gas in accumulator Sectional area of the flow Constants of gas Coefficient of discharge Coefficient of thermal capacity Density of nitrogen 48 Symbol Value Unit MN2 mT0 mA0 TT0 TA0 pT0 pA0 pAP VT VA A R Cd κ ρ0 28 19,35 0,003 293,15 293,15 30 0,1 2÷15 0,044 0,0002÷0,002 7,85×10-5 8,31 0,85 1,4 1,25 kg/mol kg kg K K MPa MPa MPa m3 m3 m3 J/mol·K kg/ m3 The model uses the ideal gas law, whereby calculation of mT0 and mA0 is given by (1). mT 0 pT 0VT RTT 0 , M N2 m A0 p A0V A RTA0 , M N2 (1) Subcritical and supercritical mass flow rate of gas was calculated based on equations (2)[8]. 2 1 pA pA pA 2 Cd A p T 0 p for p 0.528 1 p T T T m T m A , 1 p 2 1 Cd A pT 0 for A 0.528 pT 1 (2) Subcritical mass flow rate of gas is when a ratio of the pressures in accumulator and tank is greater than 0.528 [8], if not, it’s supercritical mass flow rate of gas. Temperature change rate (3)[8] is different for tank and accumulator due to expansion of gas from the tank and compressing gas in accumulator, also does not include heat exchange with the environment, because the adiabatic character of the process. TT m T m T TT TT , mT TTA m TA m T TA TA , mA (3) In the simulation modeling of the process of pumping gas through the orifice. Temperature of gas between tank and accumulator T TA calculated on the basis equation (4)[9]. T TTA T dt p A pT 1 , (4) Using above equations and ideal gas law, can be calculated the pA and pT (5). mT 0 pT m T dt RT T M N2 VT m A0 pA , 49 m A dt RT A M N2 VA , (5) 4. Results of simulation Simulation model allow estimate duration of the time of emptying accumulator what means - expansion of the gas in accumulator from preset pressure to assumed atmospheric pressure. Filling accumulator means - the gas in predetermined volume of accumulator is compressed to preset pressure of gas in accumulator. Simulations were carried out for parameters showed in table 3. Figure 4. compared the emptying time of accumulator for two cross-section areas of valve. Emptying time of accumulator, t, s 6 Cross sectional area of valve: 20 mm2, 5 Cross sectional area of valve: 50 mm2 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Initial preset pressure of gas in accumulator, pAP, MPa Fig. 4. Emptying time of accumulator through valves of cross-sectional areas: 20 and 50 mm2 These results show that doubling the cross-sectional area of valve allows reduces twice the emptying time of accumulator. It is important for a control method for this type of drive. After emptying accumulator we should fill-in accumulator to preset pressure of gas. But, after emptying, accumulator is assumed to be 90% full of oil. What means, we can filling 10% volume of accumulator. Figure 5. show filling time of accumulator to preset pressure from different pressure of gas in tank pT. b) 0,50 0,40 0,30 0,20 30 MPa 25 MPa 20 MPa 15 MPa 10 MPa Filling time of accumulator, t, s Filling time of accumulator, t, s a) 0,10 0,00 1 2 4 6 8 10 Initial preset pressure of gas in accumulator, pAP, MPa 0,50 0,40 0,30 30 MPa 25 MPa 20 MPa 15 MPa 10 MPa 0,20 0,10 0,00 1 2 4 6 8 10 Initial preset pressure of gas in accumulator, pAP, MPa Fig. 5. Filling time of accumulator to 10% of volume through valve of cross-sectional areas: a) 20 mm2 and b) 50 mm2 50 These results show impact of gas pressure in tank for filling time of accumulator and that this time can be reduced by increasing cross-section area of the valve. Based on simulation results and parameters from table 3., it was estimated that at preset pressure of gas in accumulator 2 MPa is possible to make 151 cycles of emptying and filling accumulator. Based on the assumed constant and parameters from table 3. to appointed, for preset pressure of gas in accumulator p AP in range 2÷15 MPa, empirical equation (6) allowing to estimate the possible number of cycles of emptying and filling accumulator for any set pressure in this range. i 4818,6 p AP 1,149 , (6) The equation can successfully applying this ratio to the range of the vehicle, thereby facilitating the driver or autopilot, maintaining the driving profile set to overcome the greatest possible distance. 5. Conclusion Manufacturers of components for hydraulic hybrid vehicles working to improve the design of engines and hydraulic pumps and improve their efficiency and reliability, and lower production costs. To improve control of hydraulic systems it is vital to increase the pressure at which they operate hydraulic valves and improve their reliability. To improve the collection of hydraulic energy it is important to increase the density of accumulated energy. The simulation model allows the modeling of the process of filling and emptying of pneumatic-hydraulic accumulators, Simulation allows to estimate the duration of the filling and emptying of the accumulator, This enables to estimate the number of cycles, and range the vehicle, These data allow to develop control strategies pneumatic-hydraulic drive unit. References: [1] Wydawnictwo Naukowe PWN: Definicja efektu cieplarnianego (szklarniowego) (pol.). [dostęp 11 kwietnia 2008], [2] United States Environmental Protection Agency (EPA) website, http://www.epa.gov/climatechange/ghgemissions/sources/transportation.html (link is external), [3] Baseley S., et al., Hydraulic Hybrid Systems for Commercial Vehicles, SAE technical paper, 2007, [4] PSA Peugeot Citroën and Bosch developing hydraulic hybrid powertrain for passenger cars; 30% reduction in fuel consumption in NEDC, up to 45% urban; B-segment application in 2016, Website, http://www.greencarcongress.com/2013/01/psabosch-20130122.html, [5] Jia-Shiun Chen: Energy Efficiency Comparison between Hydraulic Hybrid and Hybrid Electric Vehicles, Energies 2015, 8, 4697-4723; doi:10.3390/en8064697, [6] Mróz P., Brol S.: Conception control system of pneumatic-hydraulic drive system, Proceedings of the Institute of Vehicles x(xx)/2016, Warsaw, 2016, 51 [7] [8] [9] Shaw D., Yu J., Chieh Ch.: Design of a Hydraulic Motor System Driven by Compressed Air, Energies Vol. 6, pp. 3149-3166, 2013. Federal Emergency Management Agency, U.S. Department of transportation, U.S. Environmental Protection Agency.: Handbook of chemical hazard analysis procedures, Washington, 1989, 1-800-367-9592 in Illanois pp. 394, Bailyn, M. (1994). A Survey of Thermodynamics. New York, NY: American Institute of Physics Press. p. 21. ISBN 0-88318-797-3. Abstract The article presents a simulation model of pneumatic-hydraulic drive. The main point of this work is mathematical model, which is used to simulate the work of pneumatic-hydraulic drive. This is further used for control system synthesis and to formulate the control rules using Simulink. The process modelled is generally adiabatic expansion of a diatomic gas. Additional the low of gas from main reservoir to hydro-pneumatic accumulator is modelled and simulated. The model uses the equation of state of ideal gas by Clapeyron and process included subcritical and supercritical mass flow of gas. The simulations show that the time to empty the accumulator is more than 3 times longer than its filling. That determines the way of control of developed pneumatichydraulic drive. Keywords: pneumatic-hydraulic, simulation, model, drive, vehicle, hydraulic hybrid MODEL SYMULACYJNY NAPĘDU PNEUMATYCZNO-HYDRAULICZNEGO Streszczenie Artykuł przedstawia model symulacyjny pneumatyczno-hydraulicznej jednostki napędowej. Głównym punktem artykułu jest model matematyczny, który wykorzystywany jest w symulacji pracy pneumatyczno-hydraulicznej jednostki napędowej. Wyniki służą do syntezy układu sterowania i sformułowania reguł sterowania, używając środowiska MatLAB/SIMULINK. Modelowany proces jest procesem adiabatycznego rozprężania dwuatomowego gazu z zbiornika gazu do pneumatyczno-hydraulicznego akumulatora gazu. Model wykorzystuje równanie stanu gazu wg Clapeyrona i uwzględnia podkrytyczny i nadkrytyczny przepływ masy gazu. Symulacje pokazały, że opróżnienie akumulatora trwa ponad 3-krotnie dłużej niż jego napełnienie, co determinuje sposób sterowania rozwijanym układem pneumatyczno-hydraulicznym. Słowa kluczowe: pneumatyczno-hydrauliczny, symulacja, model, układ napędowy, pojazd, hydrauliczna hybryda 52