- Email: [email protected]
Experimental Research on Variable Hydraulic Resistors of Servo-hydraulic Valves
Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 85 (2016) 44 – 51
Sustainable Solutions for Energy and Environment, EENVIRO - YRC 2015, 18-20 November 2015, Bucharest, Romania
Experimental research on variable hydraulic resistors of servohydraulic valves Daniel Banyaia* Ioana Sfarleaa, Dan Oprutaa a
Technical University of Cluj-Napoca, Muncii Blvd, no. 103-105,Cluj-Napoca, Romania
Abstract For the nowadays industry, the hydrostatic actuation is indispensable, thus reducing the energy losses in valves that control the parameters of hydraulic energy, it has become an area of interest in applied research. The paper aims to conduct a study on hydraulic resistors, following the hydrodynamic forces that appear in an adjustable valve like a load for the valve actuator. Three types of holes (circular, rectangular, triangular) for the sleeve were assembled with each of the three spools chamfered at different angles resulting different geometry for the active edge. The results show that the variant in which the openings are rectangular and the edge of the piston is tapered at an angle of 60°, develop the lower hydrodynamic force and thus lower energy dissipation. The paper presents the experimental setup used, which offers the possibility of monitoring also the noise during operation, being able to establish the time of cavitation occurrence using spectral analyzes. The optimizations achieved by reducing the hydrodynamic forces, are important in terms of energy. ©2015 TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license © 2016 The Published by Elsevier Ltd. This Peer-review under responsibility of the organizing committee EENVIRO 2015. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 Keywords: Hydraulic resistor; servovalve; hydrodynamic force; geometry optimization
1. Introduction Flexibility is a key advantage for hydraulic and pneumatic transmissions compared with the mechanical ones, ensuring their wide use. Although, their operating principle involves low efficiency. The mechanical parameters of the energy provided by the hydraulic transmissions can be adjusted relatively simple, continuously and in large limits. Depending on the type of the hydraulic machines used the hydraulic transmissions can be: hydrostatic,
* Corresponding author E-mail address: [email protected]
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 doi:10.1016/j.egypro.2015.12.273
45
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
hydrodynamic or hydrosonic. The control hydraulic resistors are the basic elements of servo-hydraulic devices. Variable resistors are characterized by changing the fluid flow path. The paper shows the study on the resistors of type: plunger and sleeve with slots, as in Figure 1. These resistors consist of a fixed body or sleeve and a moving part, the piston called also plunger. Technological considerations made the spool resistors the most often used.[1-5]
a) Fig. 1. Cylindrical spool & sleeve resistors
b)
Fig. 2. Hydraulic resistors (Experimental models) a) Sleeve,b) Spool
The flow rate that passes through the hydraulic resistor is give by: Q=α∙A∙Ĝ (2∆p/ρ);
(1)
where: α is the coefficient of flow; A - the opening area of the resistor (throttled area). The cross sectional area (A) is a function of the position of the spool (y) and the diameter of the sleeve’s orifice (d). It may be noted that if the diameter is large, to control low flow rates, very small displacements of the spool are needed, which is difficult to obtain. The need of high accuracy variations of the flow rate, has led to the solutions shown in figure 2, some types of orifices used for spool and sleeve hydraulic resistors, where, for large openings, give small crossing areas, allowing to control low flow rates, with high precision. From the literature is known that for achieving superior transient and stationary performances for hydraulic spool resistors, is necessary: The flow regime to be turbulent, where the flow coefficient, α, is constant; Flow coefficient have a value as close to 1, which leads to low energy losses; Hydrodynamic forces to be as small (corresponding to the geometry); Dynamic behaviour is as good as possible (it is obtained by reducing the weight and increasing the pressure); Conditions to avoid the cavitation (avoiding sharp edges and decrease supply pressure) [4-6]. Some of these desiderates, (good dynamic behaviour, turbulent flow regime) are performed (assuming the downstream pressure to be equal to atmospheric pressure) at high pressure supply. Increased pressure has, however, the disadvantage of cavitation and large hydrodynamic forces. [4-6] In [6], the authors present results obtained by CFD numerical study concerning command hydraulic resistors, made in order to find an optimal geometric configuration combining different types of holes for the sleeve with plungers having different control edges. The issues under study were velocity field’s distribution, the flow regime, and the pressure field's distribution. In order to obtain static and dynamic performances as good as possible, based on the above considerations, it is necessary to find an optimum between the hydraulic energy parameters and the different geometric configurations of the resistors. The paper presents experimental results obtained using a setup illustrated in Figure 3. The measurements were conducted for different geometries of the orifices of the sleeve (circle, triangle, and rectangle) at different chamfer angles for the control edges of the spool (30°, 45° and 60°). The research undertaken within the project aims to reduce the hydrodynamic forces, obtaining a critical Re number as small as possible, avoiding the occurrence of cavitation. In spool type valves, the operating forces can be considered to be predominantly frictional and hydrodynamic. The hydrodynamic forces arise due to the change of momentum of fluid being throttled.
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Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
a)
b)
c) Fig. 3. Experimental setup; a ) Overview picture, b ) Experimental model with sensors, c ) Components scheme
2. Experimental Setup and Method The experimental setup enables the possibility to use different configurations for the two important components: spool (figure 2.b) and sleeve (figure 2.a). Also, the experimental stand allows the adjustment of the supply pressure p (bar). The transducers and data acquisition system allow direct measurements for: forces (ELAF compression and tension sensor, 250 N) on the spool and the defining flow parameters: pressure (Hydac electronic pressure transmitter 150 bar) and flow rate (Hydac electronic flow rate transmitter 1.2…20 l/min). Also, an accelerometer was included, able to detect the beginning of the cavitation phenomenon, in the strangled area, by means of structural vibrations analysis, acoustic emission (this is not the subject of this paper). [7,8,9] The acquired data can be processed to determine the hydrodynamic force, representing the only load for the actuator in steady state and the flow regime (mean velocity, Reynolds number). The data acquisition was performed using an NI acquisition board (NI USB-621x OEM), with a sample time for measurement of 250,000 samples/sec./Ch. The data processing, saving and graphic visualization, are obtained using an in-house application, made in the software MatLab Simulink. Were carried out experimental studies using nine configurations obtained by combining by one, the three sleeves (circular, triangle and rectangle orifices) with each of the three types of pistons, as follows: sleeve with circular holes with pistons having the control edge at 30°, 45° respectively 60°, the rectangular openings assembled with pistons having the control edge chamfered at 30°, 45° and 60°, finally the sleeve with triangular orifice also with the three pistons: 30°, 45° and 60°. The spool of the control hydraulic resistor is set in motion by a proportional solenoid having a 0.2 ms response time and a maximum force of 80 N. In all the results presented in the paper was given a ramp signal command to move the spool 2 mm from position “0”, for a time of 2 seconds.
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
3. Results The following figures, presents the results, for the three types of pistons assembled with the sleeve having circular orifices, at 60 bar, pressure supply. Figure 4 shows the recorded data of the pressure variation in time; in figure 5 the flow rate variation is present; figure 6 presents the values recorded for hydrodynamic forces. All the diagrams bellow are recorded at a sample time of 1.25e-2 ms.
Fig. 4. Pressure variations for circular oriffices
Fig. 5. Flow rate variations for circular oriffices
Fig. 6. Hydrodynamic forces for circular oriffices
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Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
For the rectangular holes in combination with the three types of pistons, the results concerning the pressure, flow and hydrodynamic forces, are shown in Figures 7, 8, 9.
Fig. 7. Pressure variations for rectangular oriffices
Fig. 8. Flow rate variations for rectangular oriffices
Fig. 9. Hydrodynamic forces for rectangular orifices
The time variation of the following parameters: pressure, flow and hydrodynamic forces, for the assembly: piston with edge at 30 °, 45 ° and 60° and sleeve with triangular holes, are shown in Figures 10, 11, 12.
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
Fig. 10. Pressure variations for triangular oriffices
Fig. 11. Flow rate variations for triangular oriffices
Fig. 12. Hydrodynamic forces for triangular oriffices
In Figure 13 are shown the variation of the smallest hydrodynamic forces versus the throttled area for all three the types of orifices.
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Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
Fig. 13. Hydrodynamic forces
In terms of precision all 9 models are in the same domain. The precision is defined, in the paper, as, the ability of the hydraulic resistor to maintain the parameters flow and pressure in the commanded values (60-0 bar for pressure and 0-15 l/min for the flow rate). The response time (transient regime duration) for all nine configurations of the resistors is shown in Table 1, (figures 4, 5, 7, 8, 10, 11). The maximum values for the hydrodynamic force for all nine resistors are shown in table 2, (figures 6, 9, 12). Table 1 Time response Circular
Rectangular
Triangular
30°
45°
60°
30°
45°
60°
30°
45°
60°
0.464 s
0.464 s
0.457 s
0.184 s
0.181 s
0.182 s
0.658 s
0.653 s
0.655 s
Table 2 Hydrodynamic force Circular
Rectangular
Triangular
30°
45°
60°
30°
45°
60°
30°
45°
60°
21.1 N
17.3 N
17.6 N
26.2 N
24.8 N
21.3 N
52.3 N
44.8 N
42.7 N
4. Conclusions The method presented in the paper can be used to optimize the geometry of the hydraulic resistors from the existing hydraulic devices and also in the design phase, obtaining a small hydrodynamic force results in a devices with reduced energy consumption, obtaining also the optimal time response specific to the applications where the device is included. Analysing table 1, it can be concluded that the best dynamic behaviour is manifested by the combination of: sleeve with rectangular holes and spool chamfered at 45 o, (figures 7, 8). From table 2 is found that, in terms of energy point of view, the best solution is where the hydrodynamic force is smaller so the load for the actuator is minimal: the sleeve with circular holes and piston bevelled at 45°, leading to energy reduction, (figure 6). These energy savings are achieved by optimizing the geometry of the hydraulic resistor thus not influence the dynamic behaviour. Comparing between them the results from the two tables, it can be noted, that when a small response time is needed the resistor with rectangular holes is the best solution and when is needed a low actuation force, thus the energy consumption is lower, the circular slots are the most convenient solution. The difference between circular and rectangular holes in terms of response time and hydrodynamic forces is approximately 40% in both cases, (the lowest response time for rectangular and the lowest hydrodynamic force for circular). The triangular holes have only
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
the advantage that can adjust very small differences of flow rates, through the specific of the geometry, but in terms of hydrodynamic forces, the values are much higher than in the other two variants. To improve the life cycle of the hydraulic devices, working on the spool & sleeve type resistors, the phenomenon of cavitation must be avoid by monitoring the vibration levels. The experimental stand is equipped with acoustic emissions transducer, for further spectral analysis of the noise signals, being able to provide a tool for real-time analysis of hydraulic valves, avoiding the occurrence of cavitation.
References [1] Radoi, R., Dunitrescu, C., Dutu, I., Matache, G., “Synthesis of main characteristics and common schemes used in structuring of hydraulic sources”, Magazine of Hydraulics, Pneumatics, Tribology, Ecology, Sensorics, Mechatronics, HIDRAULICA, ISSN 1453 – 7303, no. 3-4, p.61-66, 2012. [2] Marcu, I.L., “Functional parameters monitoring for an alternating flow driven hydraulic system," in Automation, Quality and Testing, Robotics, 2008. AQTR 2008. IEEE International Conference on , vol.3, no., pp.239-242, 05.2008. [3] Vaida, L., Nascutiu, L., et.al., “The increase of the functional performances of percussive rock-drills by varing its frequency” Experimental Fluid Mechanics 2006, EMT06, Liberec, ISBN 80-7372- 141-4, 2006. [4] Yanhong, B., Long, Q., „New method to improve dynamic stiffness of electro-hydraulic servo systems”, Chinese Journal of Mechanical Engineering, Volume 26, Issue 5, pp 997-1005, ISSN 1000-9345, 09.2013. [5] Li, J., Fang, X., „Stress Wave Analysis and Optical Force Measurement of Servo-Hydraulic Machine for High Strain Rate Testing”, Experimental Mechanics, Volume 54, Issue 8, pp 1497-1501, ISSN 0014-4851, 10.2014 [6] Sfarlea, I., Bode, F., Opruta, D., “The influence of the sleeve's orifices geometric patterns on the fluid flow through a hydraulic resistance”, in Experimental Fluid Mechanics EFM-2012, The European Physical Journal Conferences, vol. 45, article no. 01113, 2013. [7] Opruta, D., Vaida, L., Pleşa, A., Vaida, C., “Using Acoustic Emission in Monitoring Hydraulic Devices”, IEEE International Conference on Automation, Quality and Testing, Robotics – AQTR–2006, ISBN:1-4244-0360-X vol. 2, 2006. [8] Ilarie Bordeasu, I., Popoviciu, M., Mitelea, I., MICU, L., et.al., “Cavitation erosion resistance of ampco 45 bronze with heat treatments”, Magazine of Hydraulics, Pneumatics, Tribology, Ecology, Sensorics, Mechatronics, HIDRAULICA, ISSN 1453 – 7303, no. 2, p.53-61, 2014. [9] Marcu, I. L., Unguresan P., Nascutiu L., (2009): “Aspects Regarding the Alternating Flow Driven Hydraulic Systems”, Annals of DAAAM for 2009 &Proceedings of the 20th International DAAAM Symposium, 25-28th November 2009, Vienna, Austria, pag, 0155-0156, ISSN 1726-9679, ISBN 978-3-901509-70-4, Katalinic, B. (Ed.), Published by DAAAM International Vienna, Vienna (2009).
51
ScienceDirect Energy Procedia 85 (2016) 44 – 51
Sustainable Solutions for Energy and Environment, EENVIRO - YRC 2015, 18-20 November 2015, Bucharest, Romania
Experimental research on variable hydraulic resistors of servohydraulic valves Daniel Banyaia* Ioana Sfarleaa, Dan Oprutaa a
Technical University of Cluj-Napoca, Muncii Blvd, no. 103-105,Cluj-Napoca, Romania
Abstract For the nowadays industry, the hydrostatic actuation is indispensable, thus reducing the energy losses in valves that control the parameters of hydraulic energy, it has become an area of interest in applied research. The paper aims to conduct a study on hydraulic resistors, following the hydrodynamic forces that appear in an adjustable valve like a load for the valve actuator. Three types of holes (circular, rectangular, triangular) for the sleeve were assembled with each of the three spools chamfered at different angles resulting different geometry for the active edge. The results show that the variant in which the openings are rectangular and the edge of the piston is tapered at an angle of 60°, develop the lower hydrodynamic force and thus lower energy dissipation. The paper presents the experimental setup used, which offers the possibility of monitoring also the noise during operation, being able to establish the time of cavitation occurrence using spectral analyzes. The optimizations achieved by reducing the hydrodynamic forces, are important in terms of energy. ©2015 TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license © 2016 The Published by Elsevier Ltd. This Peer-review under responsibility of the organizing committee EENVIRO 2015. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 Keywords: Hydraulic resistor; servovalve; hydrodynamic force; geometry optimization
1. Introduction Flexibility is a key advantage for hydraulic and pneumatic transmissions compared with the mechanical ones, ensuring their wide use. Although, their operating principle involves low efficiency. The mechanical parameters of the energy provided by the hydraulic transmissions can be adjusted relatively simple, continuously and in large limits. Depending on the type of the hydraulic machines used the hydraulic transmissions can be: hydrostatic,
* Corresponding author E-mail address: [email protected]
1876-6102 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee EENVIRO 2015 doi:10.1016/j.egypro.2015.12.273
45
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
hydrodynamic or hydrosonic. The control hydraulic resistors are the basic elements of servo-hydraulic devices. Variable resistors are characterized by changing the fluid flow path. The paper shows the study on the resistors of type: plunger and sleeve with slots, as in Figure 1. These resistors consist of a fixed body or sleeve and a moving part, the piston called also plunger. Technological considerations made the spool resistors the most often used.[1-5]
a) Fig. 1. Cylindrical spool & sleeve resistors
b)
Fig. 2. Hydraulic resistors (Experimental models) a) Sleeve,b) Spool
The flow rate that passes through the hydraulic resistor is give by: Q=α∙A∙Ĝ (2∆p/ρ);
(1)
where: α is the coefficient of flow; A - the opening area of the resistor (throttled area). The cross sectional area (A) is a function of the position of the spool (y) and the diameter of the sleeve’s orifice (d). It may be noted that if the diameter is large, to control low flow rates, very small displacements of the spool are needed, which is difficult to obtain. The need of high accuracy variations of the flow rate, has led to the solutions shown in figure 2, some types of orifices used for spool and sleeve hydraulic resistors, where, for large openings, give small crossing areas, allowing to control low flow rates, with high precision. From the literature is known that for achieving superior transient and stationary performances for hydraulic spool resistors, is necessary: The flow regime to be turbulent, where the flow coefficient, α, is constant; Flow coefficient have a value as close to 1, which leads to low energy losses; Hydrodynamic forces to be as small (corresponding to the geometry); Dynamic behaviour is as good as possible (it is obtained by reducing the weight and increasing the pressure); Conditions to avoid the cavitation (avoiding sharp edges and decrease supply pressure) [4-6]. Some of these desiderates, (good dynamic behaviour, turbulent flow regime) are performed (assuming the downstream pressure to be equal to atmospheric pressure) at high pressure supply. Increased pressure has, however, the disadvantage of cavitation and large hydrodynamic forces. [4-6] In [6], the authors present results obtained by CFD numerical study concerning command hydraulic resistors, made in order to find an optimal geometric configuration combining different types of holes for the sleeve with plungers having different control edges. The issues under study were velocity field’s distribution, the flow regime, and the pressure field's distribution. In order to obtain static and dynamic performances as good as possible, based on the above considerations, it is necessary to find an optimum between the hydraulic energy parameters and the different geometric configurations of the resistors. The paper presents experimental results obtained using a setup illustrated in Figure 3. The measurements were conducted for different geometries of the orifices of the sleeve (circle, triangle, and rectangle) at different chamfer angles for the control edges of the spool (30°, 45° and 60°). The research undertaken within the project aims to reduce the hydrodynamic forces, obtaining a critical Re number as small as possible, avoiding the occurrence of cavitation. In spool type valves, the operating forces can be considered to be predominantly frictional and hydrodynamic. The hydrodynamic forces arise due to the change of momentum of fluid being throttled.
46
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
a)
b)
c) Fig. 3. Experimental setup; a ) Overview picture, b ) Experimental model with sensors, c ) Components scheme
2. Experimental Setup and Method The experimental setup enables the possibility to use different configurations for the two important components: spool (figure 2.b) and sleeve (figure 2.a). Also, the experimental stand allows the adjustment of the supply pressure p (bar). The transducers and data acquisition system allow direct measurements for: forces (ELAF compression and tension sensor, 250 N) on the spool and the defining flow parameters: pressure (Hydac electronic pressure transmitter 150 bar) and flow rate (Hydac electronic flow rate transmitter 1.2…20 l/min). Also, an accelerometer was included, able to detect the beginning of the cavitation phenomenon, in the strangled area, by means of structural vibrations analysis, acoustic emission (this is not the subject of this paper). [7,8,9] The acquired data can be processed to determine the hydrodynamic force, representing the only load for the actuator in steady state and the flow regime (mean velocity, Reynolds number). The data acquisition was performed using an NI acquisition board (NI USB-621x OEM), with a sample time for measurement of 250,000 samples/sec./Ch. The data processing, saving and graphic visualization, are obtained using an in-house application, made in the software MatLab Simulink. Were carried out experimental studies using nine configurations obtained by combining by one, the three sleeves (circular, triangle and rectangle orifices) with each of the three types of pistons, as follows: sleeve with circular holes with pistons having the control edge at 30°, 45° respectively 60°, the rectangular openings assembled with pistons having the control edge chamfered at 30°, 45° and 60°, finally the sleeve with triangular orifice also with the three pistons: 30°, 45° and 60°. The spool of the control hydraulic resistor is set in motion by a proportional solenoid having a 0.2 ms response time and a maximum force of 80 N. In all the results presented in the paper was given a ramp signal command to move the spool 2 mm from position “0”, for a time of 2 seconds.
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
3. Results The following figures, presents the results, for the three types of pistons assembled with the sleeve having circular orifices, at 60 bar, pressure supply. Figure 4 shows the recorded data of the pressure variation in time; in figure 5 the flow rate variation is present; figure 6 presents the values recorded for hydrodynamic forces. All the diagrams bellow are recorded at a sample time of 1.25e-2 ms.
Fig. 4. Pressure variations for circular oriffices
Fig. 5. Flow rate variations for circular oriffices
Fig. 6. Hydrodynamic forces for circular oriffices
47
48
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
For the rectangular holes in combination with the three types of pistons, the results concerning the pressure, flow and hydrodynamic forces, are shown in Figures 7, 8, 9.
Fig. 7. Pressure variations for rectangular oriffices
Fig. 8. Flow rate variations for rectangular oriffices
Fig. 9. Hydrodynamic forces for rectangular orifices
The time variation of the following parameters: pressure, flow and hydrodynamic forces, for the assembly: piston with edge at 30 °, 45 ° and 60° and sleeve with triangular holes, are shown in Figures 10, 11, 12.
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
Fig. 10. Pressure variations for triangular oriffices
Fig. 11. Flow rate variations for triangular oriffices
Fig. 12. Hydrodynamic forces for triangular oriffices
In Figure 13 are shown the variation of the smallest hydrodynamic forces versus the throttled area for all three the types of orifices.
49
50
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
Fig. 13. Hydrodynamic forces
In terms of precision all 9 models are in the same domain. The precision is defined, in the paper, as, the ability of the hydraulic resistor to maintain the parameters flow and pressure in the commanded values (60-0 bar for pressure and 0-15 l/min for the flow rate). The response time (transient regime duration) for all nine configurations of the resistors is shown in Table 1, (figures 4, 5, 7, 8, 10, 11). The maximum values for the hydrodynamic force for all nine resistors are shown in table 2, (figures 6, 9, 12). Table 1 Time response Circular
Rectangular
Triangular
30°
45°
60°
30°
45°
60°
30°
45°
60°
0.464 s
0.464 s
0.457 s
0.184 s
0.181 s
0.182 s
0.658 s
0.653 s
0.655 s
Table 2 Hydrodynamic force Circular
Rectangular
Triangular
30°
45°
60°
30°
45°
60°
30°
45°
60°
21.1 N
17.3 N
17.6 N
26.2 N
24.8 N
21.3 N
52.3 N
44.8 N
42.7 N
4. Conclusions The method presented in the paper can be used to optimize the geometry of the hydraulic resistors from the existing hydraulic devices and also in the design phase, obtaining a small hydrodynamic force results in a devices with reduced energy consumption, obtaining also the optimal time response specific to the applications where the device is included. Analysing table 1, it can be concluded that the best dynamic behaviour is manifested by the combination of: sleeve with rectangular holes and spool chamfered at 45 o, (figures 7, 8). From table 2 is found that, in terms of energy point of view, the best solution is where the hydrodynamic force is smaller so the load for the actuator is minimal: the sleeve with circular holes and piston bevelled at 45°, leading to energy reduction, (figure 6). These energy savings are achieved by optimizing the geometry of the hydraulic resistor thus not influence the dynamic behaviour. Comparing between them the results from the two tables, it can be noted, that when a small response time is needed the resistor with rectangular holes is the best solution and when is needed a low actuation force, thus the energy consumption is lower, the circular slots are the most convenient solution. The difference between circular and rectangular holes in terms of response time and hydrodynamic forces is approximately 40% in both cases, (the lowest response time for rectangular and the lowest hydrodynamic force for circular). The triangular holes have only
Daniel Banyai et al. / Energy Procedia 85 (2016) 44 – 51
the advantage that can adjust very small differences of flow rates, through the specific of the geometry, but in terms of hydrodynamic forces, the values are much higher than in the other two variants. To improve the life cycle of the hydraulic devices, working on the spool & sleeve type resistors, the phenomenon of cavitation must be avoid by monitoring the vibration levels. The experimental stand is equipped with acoustic emissions transducer, for further spectral analysis of the noise signals, being able to provide a tool for real-time analysis of hydraulic valves, avoiding the occurrence of cavitation.
References [1] Radoi, R., Dunitrescu, C., Dutu, I., Matache, G., “Synthesis of main characteristics and common schemes used in structuring of hydraulic sources”, Magazine of Hydraulics, Pneumatics, Tribology, Ecology, Sensorics, Mechatronics, HIDRAULICA, ISSN 1453 – 7303, no. 3-4, p.61-66, 2012. [2] Marcu, I.L., “Functional parameters monitoring for an alternating flow driven hydraulic system," in Automation, Quality and Testing, Robotics, 2008. AQTR 2008. IEEE International Conference on , vol.3, no., pp.239-242, 05.2008. [3] Vaida, L., Nascutiu, L., et.al., “The increase of the functional performances of percussive rock-drills by varing its frequency” Experimental Fluid Mechanics 2006, EMT06, Liberec, ISBN 80-7372- 141-4, 2006. [4] Yanhong, B., Long, Q., „New method to improve dynamic stiffness of electro-hydraulic servo systems”, Chinese Journal of Mechanical Engineering, Volume 26, Issue 5, pp 997-1005, ISSN 1000-9345, 09.2013. [5] Li, J., Fang, X., „Stress Wave Analysis and Optical Force Measurement of Servo-Hydraulic Machine for High Strain Rate Testing”, Experimental Mechanics, Volume 54, Issue 8, pp 1497-1501, ISSN 0014-4851, 10.2014 [6] Sfarlea, I., Bode, F., Opruta, D., “The influence of the sleeve's orifices geometric patterns on the fluid flow through a hydraulic resistance”, in Experimental Fluid Mechanics EFM-2012, The European Physical Journal Conferences, vol. 45, article no. 01113, 2013. [7] Opruta, D., Vaida, L., Pleşa, A., Vaida, C., “Using Acoustic Emission in Monitoring Hydraulic Devices”, IEEE International Conference on Automation, Quality and Testing, Robotics – AQTR–2006, ISBN:1-4244-0360-X vol. 2, 2006. [8] Ilarie Bordeasu, I., Popoviciu, M., Mitelea, I., MICU, L., et.al., “Cavitation erosion resistance of ampco 45 bronze with heat treatments”, Magazine of Hydraulics, Pneumatics, Tribology, Ecology, Sensorics, Mechatronics, HIDRAULICA, ISSN 1453 – 7303, no. 2, p.53-61, 2014. [9] Marcu, I. L., Unguresan P., Nascutiu L., (2009): “Aspects Regarding the Alternating Flow Driven Hydraulic Systems”, Annals of DAAAM for 2009 &Proceedings of the 20th International DAAAM Symposium, 25-28th November 2009, Vienna, Austria, pag, 0155-0156, ISSN 1726-9679, ISBN 978-3-901509-70-4, Katalinic, B. (Ed.), Published by DAAAM International Vienna, Vienna (2009).
51