- Email: [email protected]
Problems relating to high-pressure gear micropumps
archives of civil and mechanical engineering 14 (2014) 88–95
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/acme
Original Research Article
Problems relating to high-pressure gear micropumps W. Kolleka, P. Osin´skia, M. Stosiaka,n, A. Wilczyn´skia, P. Cichon´a,b a
Wrocław University of Technology, Faculty of Mechanical Engineering, 50-371 Wrocław, Poland UTC Aerospace Systems, 51-317 Wrocław, Poland
b
ar t ic l e in f o
abs tra ct
Article history:
This paper presents the current development trend in high-pressure hydraulic micro-
Received 28 November 2012
pumps. A survey of typical micropumps is carried out. Micropumps designed in-house,
Accepted 23 March 2013
with a delivery of 0.8 cm3/rev. and 1 cm3/rev., are presented. A special test rig was designed
Available online 2 April 2013
and built for determining the characteristics of pumps. Some of the test results are
Keywords:
reported. They indicate the necessity for further research in this area, particularly into the
Microhydraulics
encountered efficiency problems.
Micropump
& 2013 Politechnika Wroc"awska. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.
Efficiency Tests
1.
Introduction
The great advances made in microelectronics and micromechanics have opened up new possibilities for the development of fluid power microsystems, including microhydraulic equipment. In hydraulic systems the working medium is a liquid and the dimensions of the elements imparting the required flow and pressure to the liquid range from a few hundred nanometers to a few centimetres. In conventional hydrostatic drives appropriate ranges of nominal sizes (NS) are used. For example, for valves the nominal size is the nominal diameter of their flow openings, for hydraulic cylinders it is the piston diameter, for hydraulic engines— their specific absorption capacities and for displacement pumps—specific delivery. All hydraulic components with nominal sizes below 6 mm [NSo6 mm] are classified as microhydraulic.
2. Survey of available solutions and range of applications Table 1 shows some characteristic parameters (q—specific delivery/absorption capacity, Q—delivery, d—nominal diameter, pmax—nominal pressure) and dimensions (L—length, B—width, m—mass) of hydraulic elements with NSo6 and so classified as microhydraulic, manufactured by Mannesmann-Rexroth. Another parameter, besides nominal size (NS), which distinguishes microhydraulic equipment from hydraulic equipment is the rate of flow. Flows are classified, and so is microhydraulic equipment, according to the following division [1–3]:
very small flows o2 cm3/s (120 cm3/min), small flows 2–50 cm3/s (120–3000 cm3/min), medium flows 50–500 cm3/s (3–30 dm3/min),
n
Corresponding author. Tel.: +48 713204599. E-mail addresses: [email protected], [email protected] (M. Stosiak).
1644-9665/$ - see front matter & 2013 Politechnika Wroc"awska. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved. http://dx.doi.org/10.1016/j.acme.2013.03.005
89
archives of civil and mechanical engineering 14 (2014) 88–95
large flows 500–2000 cm3/s (30–120 dm3/min), very large flows 42000 cm3/s (4120 dm3/min).
3.
The flow rates in microhydraulic elements fall into the first two ranges, i.e. up to 50 cm3/s (3000 cm3/min). Thus one can conclude that in microhydraulic equipment the type series of elements are delimited by nominal sizes (NS) and flow rate ranges. Microhydraulic equipment is used in cases where relatively high powers need to be transmitted and the fluidity of motion at considerably reduced geometric dimensions must be ensured. As a result of the steady advances made in microhydraulic elements and systems, the latter increasingly often supplants pneumatic or electromechanical systems. Moreover, thanks to miniaturization, microhydraulic equipment can replace conventional hydraulic equipment in cases where the latter cannot be used because of its dimensions and mass. This applies to, among other things, medical engineering (e.g. the drives of operating tables, X-ray tables and dental chairs), the motor industry (e.g. the servomechanisms assisting steering and braking systems, automatic gearboxes, hydropneumatic suspensions, the driver's seat construction), lifting equipment, the aviation industry and the chemical and food industries (fluid flow proportioning) [14]. Hydrostatic microsystems can be employed in cases where the use of pneumatic or electromechanical systems is limited because of the requirements for great forces or high torques at the high precision of the movement of the executing element or at the ease of controlling this movement. Instead of the large conventional pneumatic or electromechanical systems, much smaller hydraulic systems can be used to transmit such forces or torques without any loss of automation ability. The principal component of each hydraulic system is a generator of hydraulic energy accumulated in the working medium being pumped. The most commonly used type of displacement pumps are gear pumps (with an estimated share of 60%). This is owing to their simple and compact design, operational reliability, high efficiency and small size [17]. The world leading manufacturers of gear pumps are Sauer Danfoss [10], offering group 0.5 pumps with unit outputs q¼ 0.25– 1.27 cm3/rev., working pressures pt ¼ 18 MPa and as high rotational speeds as nmax ¼ 5000–8000 rpm, Jihostroj [7] offering group X pumps with specific outputs q¼ 0.18–2.00 cm3/rev., forcing pressures pt ¼16–23 MPa and speeds n¼ 2800–7000 rpm, and Marzocchi Pompe [8] offering 0.25 and 0.5 series pumps with hydraulic specifications summarized in Table 2.
In-house study—universal test rig
A universal test rig, schematically shown in Figs. 1 and 2, was built for the complex experimental studying of microhydraulic elements and systems. As a part of the present study the static and dynamic characteristics of gear pumps were determined. The rig includes a gear box driven by a threephase motor with cooling. The displacement pump can be replaced with any other displacement unit with a specific delivery of 0.1–1.2 cm3/rev. Since the rig includes a control cabinet with an inverter, the rotational speed can be smoothly adjusted from 0 to 1750 rpm. Installed pump 1 is overload protected by adjustable safety valve 5. The displacement unit is loaded via throttle valve 7. Actual delivery Qrz is measured by flowmeter 6 with a measuring range of 0.01–2.0 cm3/min. Pressure gauges 8 indicate the pump forcing pressure. Pump net torque M is measured by torque meter 9 (with a measuring range of 75 Nm) connected to the meter. Rotational speed n of pump 1 is controlled by a magnetic sensor with a measuring range of 0–8000 rpm [6]. The test rig and the measurement procedure are described in more detail in [13]. The following parameters of the tested microhydraulic systems and elements were measured and recorded:
the micropump output torque, the rotational speed of the pump shaft, static and dynamic pressures, the volumetric rate of flow of the working medium.
The temperature of the working medium was controlled by a precision electronic thermometer with a digital display. Dynamic pressure was measured by a miniature piezoelectric pressure sensor. A portable signal conditioner was used as a source of supply and for conditioning the data from the dynamic ICP pressure sensor. The static pressure was controlled by an electronic pressure gauge. To put it short, one can say that depending on the measured quantity (pressure, flow rate, pump output torque, and rotational speed), the measuring circuit consisted of a given quantity sensor, a measuring amplifier, a digital oscilloscope, a PC with a dedicated software, and a printer. This configuration for measuring the principal parameters of hydraulic and mechanical microelements is characterized by
hardware–software compatibility, the simultaneous measurement of all the essential hydraulic and mechanical parameters of a hydraulic microsystem,
Table 1 – Selected hydraulic microelements with NSo6, manufactured by Mannesmann-Rexroth [1–3]. Hydraulic elements
Type
NSmin
Characteristic parameter
pmax (MPa)
L (mm)
B (mm)
m (kg)
Gear pump Multi-piston engine Non-return valve Pressure reducing valve Cartridge valve
PG2 A2FM YC DRE FTWE
4 5 4 4 2
q ¼4 cm3/rev. q ¼5.9 cm3/rev. Q ¼ 4 dm3/min d ¼4 mm d ¼2 mm
25 31.5 21 10 10
88 121 25 67 47
42 50 15 28 25
2.4 2.5 0.16 0.5 0.12
90
archives of civil and mechanical engineering 14 (2014) 88–95
Table 2 – Hydraulic-mechanical parameters of 0.25 and 0.5 group gear micropumps manufactured by Marzocchi Pompe [8]. Nominal size symbol
0.25 0.25 0.25 0.25 0.25 0.25
D D D D D D
18 24 30 36 48 60
Geometric working volume
Delivery for n ¼ 1500 rpm
Maximum rotational speed
Maximum output pressure p
Vg (cm3/rev.)
Q (dm3/min)
n (min−1)
Continuous (MPa)
Periodic (MPa)
Peak (MPa)
0.19 0.26 0.32 0.38 0.51 0.64
0.29 0.38 0.48 0.58 0.77 0.96
7000
19
21
23
Fig. 1 – Schematic of test rig: 1—gear pump, 2—cut-off valve, 3—sink filter, 4—tank, 5—adjustable safety valve, 6—flowmeter, 7—adjustable throttle valve, 8—pressure gauge, 9—torquemeter, 10—3-phase driving motor with external cooling, 11—control cabinet.
the possibility of monitoring the measuring signal value (static
pressure on the oscilloscope and on the digital display, the flow rate, the torque and the rotational speed of the pump shaft), the time-domain analysis of the signal and the real-time analysis of the frequency, directly in the course of measurement.
4.
Gear pump designed in-house
The PZO gear pump was made in-house by the Hydraulic Pumps Manufacturing Company Ltd. It is a three-plate design. The front plate has a flange for easy mounting in drive systems. The middle plate incorporates gear wheels,
91
archives of civil and mechanical engineering 14 (2014) 88–95
slide bearing housings and suction and forcing holes for connecting to a hydraulic system. The whole construction is closed with a rear plate and bolted together. The gear
wheels turn in cavities in the middle plate. The driving wheel is driven by a driving shaft and meshes with the driven wheel.
Fig. 2 – Real delivery and torque characteristics of micropump with unit delivery q ¼1.0 cm3/rev. for HL 68, n ¼ 1500 rpm [13]. Table 3 – Meshing parameters [13]. Parameters
Specific unit delivery (cm3/rev.)
Symbol and unit
Number of teeth Modulus Pressure angle Addendum coefficient Correction coefficient Rim width Distance between axles Rolling pressure angle
z [–] m0 [mm] α0 [1] y [–] x [–] b [mm] a [–] αt [1]
0.25
0.31
0.5
0.8
1.0
14 1 20 1 0.61 2.32 15 28.71
14 1 20 1 0.61 2.92 15 28.71
14 1 20 1 0.61 4.64 15 28.71
14 1 20 1 0.61 7.42 15 28.71
14 1 20 1 0.61 9.28 15 28.71
Table 4 – Measurement results for pump PZO 1.0 cm3/rev., series X10050010 (oil HL 68) [13] for micropump shaft rotational speed of 1000 and 1500 rpm. n (rpm)
pt (MPa)
Qrz (dm3/min)
M (Nm)
Nm (W)
Nh (W)
ηv (%)
ηhm (%)
ηc (%)
1000
≈0 6 10 16 20 22
0.768 0.725 0.698 0.653 0.613 0.576
0.16 0.84 1.38 2.25 2.95 3.30
16.76 87.96 144.51 235.62 308.92 345.58
5.50 72.50 116.33 174.13 204.33 211.20
100.00 94.40 90.89 85.03 79.82 75.00
32.85 87.31 88.57 86.92 82.87 81.49
32.85 82.42 80.50 73.90 66.14 61.12
1500
≈0 6 10 16 20 22
1.151 1.123 1.112 1.075 1.036 1.011
0.22 0.87 1.41 2.29 2.90 3.23
34.56 136.66 221.48 359.71 455.53 507.37
12.85 112.30 185.33 286.67 345.33 370.70
100.00 97.57 96.61 93.40 90.01 87.84
37.19 84.22 86.61 85.33 84.22 83.18
37.19 82.18 83.68 79.69 75.81 73.06
92
archives of civil and mechanical engineering 14 (2014) 88–95
Measurements were carried out on five PZ0 pumps with a unit delivery of 0.25–1.00 cm3/rev. The meshing parameters of the tested pumps are shown in Table 3. The static characteristics were determined at a constant temperature of the working medium, i.e. at 40 1C, for two different types of hydraulic oil: Azolla ZS 22 and HL 68. The kinematic viscosities at the adopted operating temperature were respectively ν ¼ 65.6 cSt for HL 68 and ν ¼ 22.5 cSt for Azolla ZS 22. The measurements were performed for constant shaft
rotational speeds n ¼ 500, 750, 1000, 1250, 1500, and 1750 rpm. Readings were taken at forcing pressures pt ¼0, 1, 2, 3,…, 22 MPa. The tests have shown that the shape of the static characteristics of the prototype units is mainly determined by the viscosity of the oil. By far the best diagrams were obtained for oil HL 68 whose viscosity is almost three times higher than that of Azolla ZS 22. The higher viscosity contributed to better overall efficiency and volumetric efficiency and to a slight
Fig. 3 – Hydraulic power and total power characteristics of micropump with unit delivery q¼1.0 cm3/rev. for HL 68, n¼ 1500 rpm [13].
Fig. 4 – Efficiency characteristic of micropump with unit delivery q¼ 1.0 cm3/rev. for HL 68, n ¼1500 rpm [13].
archives of civil and mechanical engineering 14 (2014) 88–95
93
Fig. 5 – Real delivery and torque characteristics of micropump with unit delivery q¼ 0.8 cm3/rev. for HL 68, n ¼1500 rpm.
Fig. 6 – Hydraulic power and total power of micropump with unit deliver q¼ 0.8 cm3/rev. for HL 68, n ¼1500 rpm.
increase in hydraulic–mechanical efficiency. In the case of the pump with a unit delivery of 1 cm3/rev. and the Azolla ZS 22 oil, the following efficiencies were obtained for the pressures and the nominal rpm: ηv ¼ 52.5%, ηhm ¼ 76.0% and ηc ¼39.9% while for the HL 68 oil the obtained efficiencies were ηv ¼ 90.0%, ηhm ¼84.2% and ηc ¼ 75.8%. A summary of the results of measuring the static characteristics of the PZO pump (serial number X10050010) with a unit delivery of 1.0 cm3/rev. for oil HL 68 is presented in Table 4.
The static characteristics for the prototype micropump with unit delivery q¼ 1.0 cm3/rev. and for the pump with unit delivery q¼ 0.8 cm3/rev., with hydraulic oil HL 68 (temp. 40 1C) used in both of them, are shown in respectively Figs. 2–4 and Figs. 5–7. Difficulties in obtaining high working pressures were encountered when the oil characterized by lower viscosity was used. The difficulties were due to high internal leakage, as a result of which the volumetric efficiency was close to
94
archives of civil and mechanical engineering 14 (2014) 88–95
Fig. 7 – Efficiency characteristic of pump with unit delivery q¼0.8 cm3/rev. for HL 68, n¼ 1500 rpm.
zero. Therefore if the pumps were to be used to pump low viscosity liquids, the dimensional tolerances should be tightened and the axial and radial clearances between the gear wheels and the housings of the slide bearings should be reduced. This means that the pumps are dedicated to oils characterized by working viscosities in a range of 65–70 cSt [13].
5.
Conclusion
The results of research aimed at designing and testing of a new type series of internal-meshing gear micropumps have been presented. It has been found that for nominal pressures and nominal micropump shaft rotational speeds the achieved volumetric and total efficiencies are not satisfactory when a lower viscosity oil, e.g. Azolla ZS 22, is used in the system. According to the general guidelines for oils for microhydraulic systems in the considered application area one should use oils with lower viscosity in order to reduce the heating up of the working liquid (and of the other components of a microhydraulic system) and flow losses (mainly in hydraulic ducts). Therefore there is a need to conduct further simulation, design, constructional and process research on the development of gear micropumps in order to improve their efficiency for the recommended hydraulic oils. The CFD methods, by means of which one can determine the distribution of the total velocity of the liquid flowing through a hydraulic microelement and the distribution of pressure in a selected cross-section of a hydraulic microelement, and study the phenomena (e.g. cavitation) associated with the flow of a liquid through a hydraulic microelement, can be useful in simulations and for creating numerical models. The
application of numerical simulation methods based on CFD for this purpose can be found in, e.g., [15,16].
r e f e r e n c e s
[1] R. Dindorf, P. Łaski, J. Wołkow, Drive and fluid microelement control engineering (in Polish), in: Proceedings of the 10th Conference CYLINDER 2000. The Study, Design, Manufacturing and Operation of Hydraulic Systems, 09.2000, Szczyrk, pp. 49–54. [2] R. Dindorf, J. Wołkow, Microhydraulics, Hydraulics and Pneumatics (in Polish), Issue 6/99, 1999, pp.16–19. [3] R. Dindorf, J. Wołkow, Microhydraulics in automotive vehicles (in Polish), Portfolio of Motorization Scientific Problems Committee, vol. 20, 2000, ISBN:83-910107-4-0. [6] User's Manual for SensorAT Meter and Torquemeter Type MT-5, MT-10, MT-20, MT-50, MT-100, MT-200, MT-500, MT1000 (in Polish). [7] A.S. Jihostroj, Aerotechnology & Hydraulics Catalogue. [8] Marzocchi Pompe Catalogue: Micropompe ad Ingranaggi, Gear micropumps 0.25-0.5, September 2006. [10] Sauer Danfoss catalogue: general gear pumps and gear motors, Technical Information, January 2008. [13] W. Kollek, Fundamentals of design, modelling and operation of microhydraulic elements and systems (in Polish), Wrocław University of Technology Publishing House, Wrocław, 2011. [14] M. Byung-Phil, S. Mi-Young, J. Ho-Seung, K. Chul-Ju, Fabrication of a no-leakage micro-valve with a freefloating structure for a drug-delivery system, Journal of the Korean Physical Society 43 (5) (2003) 930–934. [15] F. Wilczyński, M. Zawiślak, Analysis of technical parameters of valve PN16 (in Polish), in: Proceedings of Hydraulic and Pneumatic Drives and Controls Conference 2009: Domestic Sector in Turbulent Market Conditions,
archives of civil and mechanical engineering 14 (2014) 88–95
International Science & Technology Conference, Wrocław, 7– 9 October 2009, Wrocław SIMP Personnel Training Centre, pp. 354–359. [16] T. Tabaczek, M. Zawiślak, A. Zieliński, Computations of flow with cavitation in centrifugal pump (in Polish), Systems:
95
Journal of Transdisciplinary Systems Science 16 (2) (2012) 385–394. [17] W. Kollek, P. Osiński, Modelling and Design of Gear Pumps, Wrocław University of Technology Publishing House, Wrocław, 2009.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/acme
Original Research Article
Problems relating to high-pressure gear micropumps W. Kolleka, P. Osin´skia, M. Stosiaka,n, A. Wilczyn´skia, P. Cichon´a,b a
Wrocław University of Technology, Faculty of Mechanical Engineering, 50-371 Wrocław, Poland UTC Aerospace Systems, 51-317 Wrocław, Poland
b
ar t ic l e in f o
abs tra ct
Article history:
This paper presents the current development trend in high-pressure hydraulic micro-
Received 28 November 2012
pumps. A survey of typical micropumps is carried out. Micropumps designed in-house,
Accepted 23 March 2013
with a delivery of 0.8 cm3/rev. and 1 cm3/rev., are presented. A special test rig was designed
Available online 2 April 2013
and built for determining the characteristics of pumps. Some of the test results are
Keywords:
reported. They indicate the necessity for further research in this area, particularly into the
Microhydraulics
encountered efficiency problems.
Micropump
& 2013 Politechnika Wroc"awska. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved.
Efficiency Tests
1.
Introduction
The great advances made in microelectronics and micromechanics have opened up new possibilities for the development of fluid power microsystems, including microhydraulic equipment. In hydraulic systems the working medium is a liquid and the dimensions of the elements imparting the required flow and pressure to the liquid range from a few hundred nanometers to a few centimetres. In conventional hydrostatic drives appropriate ranges of nominal sizes (NS) are used. For example, for valves the nominal size is the nominal diameter of their flow openings, for hydraulic cylinders it is the piston diameter, for hydraulic engines— their specific absorption capacities and for displacement pumps—specific delivery. All hydraulic components with nominal sizes below 6 mm [NSo6 mm] are classified as microhydraulic.
2. Survey of available solutions and range of applications Table 1 shows some characteristic parameters (q—specific delivery/absorption capacity, Q—delivery, d—nominal diameter, pmax—nominal pressure) and dimensions (L—length, B—width, m—mass) of hydraulic elements with NSo6 and so classified as microhydraulic, manufactured by Mannesmann-Rexroth. Another parameter, besides nominal size (NS), which distinguishes microhydraulic equipment from hydraulic equipment is the rate of flow. Flows are classified, and so is microhydraulic equipment, according to the following division [1–3]:
very small flows o2 cm3/s (120 cm3/min), small flows 2–50 cm3/s (120–3000 cm3/min), medium flows 50–500 cm3/s (3–30 dm3/min),
n
Corresponding author. Tel.: +48 713204599. E-mail addresses: [email protected], [email protected] (M. Stosiak).
1644-9665/$ - see front matter & 2013 Politechnika Wroc"awska. Published by Elsevier Urban & Partner Sp. z o.o. All rights reserved. http://dx.doi.org/10.1016/j.acme.2013.03.005
89
archives of civil and mechanical engineering 14 (2014) 88–95
large flows 500–2000 cm3/s (30–120 dm3/min), very large flows 42000 cm3/s (4120 dm3/min).
3.
The flow rates in microhydraulic elements fall into the first two ranges, i.e. up to 50 cm3/s (3000 cm3/min). Thus one can conclude that in microhydraulic equipment the type series of elements are delimited by nominal sizes (NS) and flow rate ranges. Microhydraulic equipment is used in cases where relatively high powers need to be transmitted and the fluidity of motion at considerably reduced geometric dimensions must be ensured. As a result of the steady advances made in microhydraulic elements and systems, the latter increasingly often supplants pneumatic or electromechanical systems. Moreover, thanks to miniaturization, microhydraulic equipment can replace conventional hydraulic equipment in cases where the latter cannot be used because of its dimensions and mass. This applies to, among other things, medical engineering (e.g. the drives of operating tables, X-ray tables and dental chairs), the motor industry (e.g. the servomechanisms assisting steering and braking systems, automatic gearboxes, hydropneumatic suspensions, the driver's seat construction), lifting equipment, the aviation industry and the chemical and food industries (fluid flow proportioning) [14]. Hydrostatic microsystems can be employed in cases where the use of pneumatic or electromechanical systems is limited because of the requirements for great forces or high torques at the high precision of the movement of the executing element or at the ease of controlling this movement. Instead of the large conventional pneumatic or electromechanical systems, much smaller hydraulic systems can be used to transmit such forces or torques without any loss of automation ability. The principal component of each hydraulic system is a generator of hydraulic energy accumulated in the working medium being pumped. The most commonly used type of displacement pumps are gear pumps (with an estimated share of 60%). This is owing to their simple and compact design, operational reliability, high efficiency and small size [17]. The world leading manufacturers of gear pumps are Sauer Danfoss [10], offering group 0.5 pumps with unit outputs q¼ 0.25– 1.27 cm3/rev., working pressures pt ¼ 18 MPa and as high rotational speeds as nmax ¼ 5000–8000 rpm, Jihostroj [7] offering group X pumps with specific outputs q¼ 0.18–2.00 cm3/rev., forcing pressures pt ¼16–23 MPa and speeds n¼ 2800–7000 rpm, and Marzocchi Pompe [8] offering 0.25 and 0.5 series pumps with hydraulic specifications summarized in Table 2.
In-house study—universal test rig
A universal test rig, schematically shown in Figs. 1 and 2, was built for the complex experimental studying of microhydraulic elements and systems. As a part of the present study the static and dynamic characteristics of gear pumps were determined. The rig includes a gear box driven by a threephase motor with cooling. The displacement pump can be replaced with any other displacement unit with a specific delivery of 0.1–1.2 cm3/rev. Since the rig includes a control cabinet with an inverter, the rotational speed can be smoothly adjusted from 0 to 1750 rpm. Installed pump 1 is overload protected by adjustable safety valve 5. The displacement unit is loaded via throttle valve 7. Actual delivery Qrz is measured by flowmeter 6 with a measuring range of 0.01–2.0 cm3/min. Pressure gauges 8 indicate the pump forcing pressure. Pump net torque M is measured by torque meter 9 (with a measuring range of 75 Nm) connected to the meter. Rotational speed n of pump 1 is controlled by a magnetic sensor with a measuring range of 0–8000 rpm [6]. The test rig and the measurement procedure are described in more detail in [13]. The following parameters of the tested microhydraulic systems and elements were measured and recorded:
the micropump output torque, the rotational speed of the pump shaft, static and dynamic pressures, the volumetric rate of flow of the working medium.
The temperature of the working medium was controlled by a precision electronic thermometer with a digital display. Dynamic pressure was measured by a miniature piezoelectric pressure sensor. A portable signal conditioner was used as a source of supply and for conditioning the data from the dynamic ICP pressure sensor. The static pressure was controlled by an electronic pressure gauge. To put it short, one can say that depending on the measured quantity (pressure, flow rate, pump output torque, and rotational speed), the measuring circuit consisted of a given quantity sensor, a measuring amplifier, a digital oscilloscope, a PC with a dedicated software, and a printer. This configuration for measuring the principal parameters of hydraulic and mechanical microelements is characterized by
hardware–software compatibility, the simultaneous measurement of all the essential hydraulic and mechanical parameters of a hydraulic microsystem,
Table 1 – Selected hydraulic microelements with NSo6, manufactured by Mannesmann-Rexroth [1–3]. Hydraulic elements
Type
NSmin
Characteristic parameter
pmax (MPa)
L (mm)
B (mm)
m (kg)
Gear pump Multi-piston engine Non-return valve Pressure reducing valve Cartridge valve
PG2 A2FM YC DRE FTWE
4 5 4 4 2
q ¼4 cm3/rev. q ¼5.9 cm3/rev. Q ¼ 4 dm3/min d ¼4 mm d ¼2 mm
25 31.5 21 10 10
88 121 25 67 47
42 50 15 28 25
2.4 2.5 0.16 0.5 0.12
90
archives of civil and mechanical engineering 14 (2014) 88–95
Table 2 – Hydraulic-mechanical parameters of 0.25 and 0.5 group gear micropumps manufactured by Marzocchi Pompe [8]. Nominal size symbol
0.25 0.25 0.25 0.25 0.25 0.25
D D D D D D
18 24 30 36 48 60
Geometric working volume
Delivery for n ¼ 1500 rpm
Maximum rotational speed
Maximum output pressure p
Vg (cm3/rev.)
Q (dm3/min)
n (min−1)
Continuous (MPa)
Periodic (MPa)
Peak (MPa)
0.19 0.26 0.32 0.38 0.51 0.64
0.29 0.38 0.48 0.58 0.77 0.96
7000
19
21
23
Fig. 1 – Schematic of test rig: 1—gear pump, 2—cut-off valve, 3—sink filter, 4—tank, 5—adjustable safety valve, 6—flowmeter, 7—adjustable throttle valve, 8—pressure gauge, 9—torquemeter, 10—3-phase driving motor with external cooling, 11—control cabinet.
the possibility of monitoring the measuring signal value (static
pressure on the oscilloscope and on the digital display, the flow rate, the torque and the rotational speed of the pump shaft), the time-domain analysis of the signal and the real-time analysis of the frequency, directly in the course of measurement.
4.
Gear pump designed in-house
The PZO gear pump was made in-house by the Hydraulic Pumps Manufacturing Company Ltd. It is a three-plate design. The front plate has a flange for easy mounting in drive systems. The middle plate incorporates gear wheels,
91
archives of civil and mechanical engineering 14 (2014) 88–95
slide bearing housings and suction and forcing holes for connecting to a hydraulic system. The whole construction is closed with a rear plate and bolted together. The gear
wheels turn in cavities in the middle plate. The driving wheel is driven by a driving shaft and meshes with the driven wheel.
Fig. 2 – Real delivery and torque characteristics of micropump with unit delivery q ¼1.0 cm3/rev. for HL 68, n ¼ 1500 rpm [13]. Table 3 – Meshing parameters [13]. Parameters
Specific unit delivery (cm3/rev.)
Symbol and unit
Number of teeth Modulus Pressure angle Addendum coefficient Correction coefficient Rim width Distance between axles Rolling pressure angle
z [–] m0 [mm] α0 [1] y [–] x [–] b [mm] a [–] αt [1]
0.25
0.31
0.5
0.8
1.0
14 1 20 1 0.61 2.32 15 28.71
14 1 20 1 0.61 2.92 15 28.71
14 1 20 1 0.61 4.64 15 28.71
14 1 20 1 0.61 7.42 15 28.71
14 1 20 1 0.61 9.28 15 28.71
Table 4 – Measurement results for pump PZO 1.0 cm3/rev., series X10050010 (oil HL 68) [13] for micropump shaft rotational speed of 1000 and 1500 rpm. n (rpm)
pt (MPa)
Qrz (dm3/min)
M (Nm)
Nm (W)
Nh (W)
ηv (%)
ηhm (%)
ηc (%)
1000
≈0 6 10 16 20 22
0.768 0.725 0.698 0.653 0.613 0.576
0.16 0.84 1.38 2.25 2.95 3.30
16.76 87.96 144.51 235.62 308.92 345.58
5.50 72.50 116.33 174.13 204.33 211.20
100.00 94.40 90.89 85.03 79.82 75.00
32.85 87.31 88.57 86.92 82.87 81.49
32.85 82.42 80.50 73.90 66.14 61.12
1500
≈0 6 10 16 20 22
1.151 1.123 1.112 1.075 1.036 1.011
0.22 0.87 1.41 2.29 2.90 3.23
34.56 136.66 221.48 359.71 455.53 507.37
12.85 112.30 185.33 286.67 345.33 370.70
100.00 97.57 96.61 93.40 90.01 87.84
37.19 84.22 86.61 85.33 84.22 83.18
37.19 82.18 83.68 79.69 75.81 73.06
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Measurements were carried out on five PZ0 pumps with a unit delivery of 0.25–1.00 cm3/rev. The meshing parameters of the tested pumps are shown in Table 3. The static characteristics were determined at a constant temperature of the working medium, i.e. at 40 1C, for two different types of hydraulic oil: Azolla ZS 22 and HL 68. The kinematic viscosities at the adopted operating temperature were respectively ν ¼ 65.6 cSt for HL 68 and ν ¼ 22.5 cSt for Azolla ZS 22. The measurements were performed for constant shaft
rotational speeds n ¼ 500, 750, 1000, 1250, 1500, and 1750 rpm. Readings were taken at forcing pressures pt ¼0, 1, 2, 3,…, 22 MPa. The tests have shown that the shape of the static characteristics of the prototype units is mainly determined by the viscosity of the oil. By far the best diagrams were obtained for oil HL 68 whose viscosity is almost three times higher than that of Azolla ZS 22. The higher viscosity contributed to better overall efficiency and volumetric efficiency and to a slight
Fig. 3 – Hydraulic power and total power characteristics of micropump with unit delivery q¼1.0 cm3/rev. for HL 68, n¼ 1500 rpm [13].
Fig. 4 – Efficiency characteristic of micropump with unit delivery q¼ 1.0 cm3/rev. for HL 68, n ¼1500 rpm [13].
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Fig. 5 – Real delivery and torque characteristics of micropump with unit delivery q¼ 0.8 cm3/rev. for HL 68, n ¼1500 rpm.
Fig. 6 – Hydraulic power and total power of micropump with unit deliver q¼ 0.8 cm3/rev. for HL 68, n ¼1500 rpm.
increase in hydraulic–mechanical efficiency. In the case of the pump with a unit delivery of 1 cm3/rev. and the Azolla ZS 22 oil, the following efficiencies were obtained for the pressures and the nominal rpm: ηv ¼ 52.5%, ηhm ¼ 76.0% and ηc ¼39.9% while for the HL 68 oil the obtained efficiencies were ηv ¼ 90.0%, ηhm ¼84.2% and ηc ¼ 75.8%. A summary of the results of measuring the static characteristics of the PZO pump (serial number X10050010) with a unit delivery of 1.0 cm3/rev. for oil HL 68 is presented in Table 4.
The static characteristics for the prototype micropump with unit delivery q¼ 1.0 cm3/rev. and for the pump with unit delivery q¼ 0.8 cm3/rev., with hydraulic oil HL 68 (temp. 40 1C) used in both of them, are shown in respectively Figs. 2–4 and Figs. 5–7. Difficulties in obtaining high working pressures were encountered when the oil characterized by lower viscosity was used. The difficulties were due to high internal leakage, as a result of which the volumetric efficiency was close to
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Fig. 7 – Efficiency characteristic of pump with unit delivery q¼0.8 cm3/rev. for HL 68, n¼ 1500 rpm.
zero. Therefore if the pumps were to be used to pump low viscosity liquids, the dimensional tolerances should be tightened and the axial and radial clearances between the gear wheels and the housings of the slide bearings should be reduced. This means that the pumps are dedicated to oils characterized by working viscosities in a range of 65–70 cSt [13].
5.
Conclusion
The results of research aimed at designing and testing of a new type series of internal-meshing gear micropumps have been presented. It has been found that for nominal pressures and nominal micropump shaft rotational speeds the achieved volumetric and total efficiencies are not satisfactory when a lower viscosity oil, e.g. Azolla ZS 22, is used in the system. According to the general guidelines for oils for microhydraulic systems in the considered application area one should use oils with lower viscosity in order to reduce the heating up of the working liquid (and of the other components of a microhydraulic system) and flow losses (mainly in hydraulic ducts). Therefore there is a need to conduct further simulation, design, constructional and process research on the development of gear micropumps in order to improve their efficiency for the recommended hydraulic oils. The CFD methods, by means of which one can determine the distribution of the total velocity of the liquid flowing through a hydraulic microelement and the distribution of pressure in a selected cross-section of a hydraulic microelement, and study the phenomena (e.g. cavitation) associated with the flow of a liquid through a hydraulic microelement, can be useful in simulations and for creating numerical models. The
application of numerical simulation methods based on CFD for this purpose can be found in, e.g., [15,16].
r e f e r e n c e s
[1] R. Dindorf, P. Łaski, J. Wołkow, Drive and fluid microelement control engineering (in Polish), in: Proceedings of the 10th Conference CYLINDER 2000. The Study, Design, Manufacturing and Operation of Hydraulic Systems, 09.2000, Szczyrk, pp. 49–54. [2] R. Dindorf, J. Wołkow, Microhydraulics, Hydraulics and Pneumatics (in Polish), Issue 6/99, 1999, pp.16–19. [3] R. Dindorf, J. Wołkow, Microhydraulics in automotive vehicles (in Polish), Portfolio of Motorization Scientific Problems Committee, vol. 20, 2000, ISBN:83-910107-4-0. [6] User's Manual for SensorAT Meter and Torquemeter Type MT-5, MT-10, MT-20, MT-50, MT-100, MT-200, MT-500, MT1000 (in Polish). [7] A.S. Jihostroj, Aerotechnology & Hydraulics Catalogue. [8] Marzocchi Pompe Catalogue: Micropompe ad Ingranaggi, Gear micropumps 0.25-0.5, September 2006. [10] Sauer Danfoss catalogue: general gear pumps and gear motors, Technical Information, January 2008. [13] W. Kollek, Fundamentals of design, modelling and operation of microhydraulic elements and systems (in Polish), Wrocław University of Technology Publishing House, Wrocław, 2011. [14] M. Byung-Phil, S. Mi-Young, J. Ho-Seung, K. Chul-Ju, Fabrication of a no-leakage micro-valve with a freefloating structure for a drug-delivery system, Journal of the Korean Physical Society 43 (5) (2003) 930–934. [15] F. Wilczyński, M. Zawiślak, Analysis of technical parameters of valve PN16 (in Polish), in: Proceedings of Hydraulic and Pneumatic Drives and Controls Conference 2009: Domestic Sector in Turbulent Market Conditions,
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International Science & Technology Conference, Wrocław, 7– 9 October 2009, Wrocław SIMP Personnel Training Centre, pp. 354–359. [16] T. Tabaczek, M. Zawiślak, A. Zieliński, Computations of flow with cavitation in centrifugal pump (in Polish), Systems:
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Journal of Transdisciplinary Systems Science 16 (2) (2012) 385–394. [17] W. Kollek, P. Osiński, Modelling and Design of Gear Pumps, Wrocław University of Technology Publishing House, Wrocław, 2009.