INTERCONNECTION POSSIBILITIES FOR THE WORKING VOLUMES OF THE ALTERNATING HYDRAULIC MOTORS

Transcription

1 Scientific Bulletin of the Politehnica University of Timisoara Transactions on Mechanics Special issue The 6 th International Conference on Hydraulic Machinery and Hydrodynamics Timisoara, Romania, October 21-22, 24 INTERCONNECTION POSSIBILITIES FOR THE WORKING VOLUMES OF THE ALTERNATING HYDRAULIC MOTORS Ioan-Lucian MARCU, Assist. Eng.* Department of Machine-Tools and Industrial Robots Technical University of Cluj-Napoca Ioan I. POP, Prof. Dr. Eng. Department of Machine-Tools and Industrial Robots Technical University of Cluj-Napoca *Corresponding author: Bv Muncii 13-15, 3223, Cluj-Napoca, Romania Tel.: (+4) , Fax: (+4) , lucian_marcu@yahoo.com ABSTRACT This paper presents the interconnection possibilities for the working volumes of the alternating hydraulic motor with alternating flow and pressure energy generator and the obtained experimental results. A specific characteristic of this type of motors consists in the fact that the working volumes of each phase are independently connected, through pipes, with the chambers of the pistons of the generator. In principle, within these systems, the active stroke (drive) of the pistons, is produced by the pressurized fluid flow from the generator, while, for the retraction (return) stroke there is necessary a supplementary connection to a pressure generator, working in opposite phase with respect to the first one. The pistons can be connected either in a star or delta configuration. In addition, the paper presents a comparison between the conclusions, the advantages and drawbacks of each interconnection solution, which resulted from the experimental analysis. KEYWORDS Alternating flow, star and delta connections NOMENCLATURE C S [m 4 /N] sonic capacity L [N s 2 /m 5 ] fluid inertia p [bar] harmonic pressure p st [bar] static pressure Q [m 3 /s] harmonic flow R [N s/m 5 ] flow resistance t [s] time ϕ [rad] phase angle ω [rad/s] angular frequency Subscripts and Superscripts amax amplitude of an alternative parameter i instantaneous parameter C capacitive influence L inertial influence R resistive (frictional) influence 1. THEORETICAL APPROACHES All known methods of power transmission by fluid, and their applications, are based on continues pressure, and flow circulation, which are achieved by the pump, and collecting by final elements, we considered fluid is uncompressible. Sonic theory is based on elasticity (compressibility) of energy transmission medium. Thus, energy is transmitted forward from point to point by compression and expansion (oscillation) of fluid mass, which has an effect of longitudinal oscillation, which moves along the fluid line. Fluid mechanics and applications of hydraulics so far, mostly not considered the fluid elasticity, mentioned before, but are the most important characteristics of the transmitted medium. If is considered a hydraulic system in which every working volume of an alternating motor is connected independently, by a phase pipe, with the corresponding working volume of an generator, then any modification of the volume of the generator will produce an alternative flow and pressure transmitted along the phase line to the motor. The equation that defining the instantaneous alternative flow and pressure are: [1, 3, 4] i i ( ω t + ϕ ) sin( ω t + ϕ ) Q = Q sin (1) p = p + p (2) st Making a complete analysis of an hydraulic system working with alternative flow require to taking account some parameters which define the fall of pressure 365

2 along the line do to the friction, inertia and elasticity (compressibility) of the fluid. The fall of the instantaneous pressure do to the friction along the line will be: [3, 4] i R f ( ωt ϕ ) p = R Q sin + (3) The Eq. 5 demonstrates the fact that the instantaneous flow is in phase with the fall of pressure through the resistance. The fall of pressure do to fluid inertia is: [3, 4] i L ( ωt ϕ ) p = ω L Q cos + (4) The phase vector of the inductive fall of pressure is advanced with 9 in comparison to the instantaneous flow. If we consider the elasticity of the transmitting medium, the capacitive fall of pressure is: [3, 4] Q p + ( ωt ϕ ) ic = cos (5) CS ω It can be noticed the fact that the vector of falling capacitive pressure is behind it with 9 in comparison to the instantaneous flow. 2. EXPERIMENTAL RESEARCHES REGARDING ROTARY HYDRAULIC MOTORS USING ALTERNATING FLOWS The designed rotary hydraulic motor working with alternating flows was tested on an experimental stand. The construction allows two types of interconnection configurations between the phase pipes and motor working volumes (cylinder chambers), which are in star or in delta, each of them with their individual particularities. In principle, the designed rotary hydraulic motor consist in three associated hydraulic double end cylinders, with small dimensions, which act individually to an output shaft, obtaining in this way a rotational movement of this. In Figure 1 is presented schematically the star interconnection configuration of the working volumes of the motor cylinders. Figure 1 shows that each phase pipe (line) is connected individually to a working volume of the motor cylinders, providing in this way the active stroke of the pistons. The working volumes (chambers) of the cylinders are interconnected. In this way, if we taking account that the movement of each piston have a difference of the phase on 12, the advance of one motor piston will generate a same flow in the star connection, which provide the retraction stroke (idling stroke) of the next two pistons. A photo of the motor connected in star configuration is presented in Figure 2. Figure 1. Principle of the star interconnection Figure 2. The star interconnection of the motor A characteristic of the star connection is that the sum of alternating flows in the connection point is theoretically zero. The delta interconnection configuration is presented schematically in Figure 3, and also a photo of the motor in Figure 4. Figure 3. Principle of the delta interconnection 366

3 Figure 4. The delta interconnection of the motor The delta connection involve that each first working volume of an cylinder, which is providing the active stroke, is connected with the second working volume of the next phase cylinder, providing in this way his retraction stroke (idling stroke), the pressures in this chambers being, of course theoretically, at the same values. Schematically the entire transmission system is presented in Figure 5. The alternating flows and pressures are provided by a generator 2, acted by a continuous current electric motor 1, and transmitted along of three phase pipes having 1 m length, to a special designed rotary hydraulic motor assembly 4. The motor contains three double end hydraulic cylinders which act individually some pulleys 5, having mounted inside drawn cup roller clutches and in this way the rotational motion and also the torque is transmitted unidirectional to the output shaft of the motor. Because the functioning of the prototype was tested in idling condition and also loaded, the output shaft was coupled to a braking device 9, acted by a small hydraulic cylinder, which allows loading on the shaft torques at different values. Testing that kind of system involve a precisely control of the mechanic and hydraulic parameters, and so collecting as experimental data is possible. To do so, was mounted some proximity sensors 6, pressure sensors 7 and displacement sensors 8. Figure 5. Principle schema of the Three-phase hydraulic system working with alternating flows 3. EXPERIMENTAL RESULTS To collect the primary experimental data regarding the functioning parameters of the rotary hydraulic motor working with alternating flows and so for the entire system we used LabView programs and an acquisition board connected to the mounted sensors. The design of some components and of the entire transmission system like the electric command assembly and the generator allowed to modify the rotational speed of the generator, the stroke of his pistons and so the static pressure which load initial the connection lines (pipes). Also the construction of the motor allowed using two different types of interconnection configurations, in star or in delta, between the working volumes. Taking account of these possibilities to vary the initial conditions, we obtained simultaneously a large amount of experimental data, for each configuration, regarding rotational speeds of the generator and motor, the strokes of motor pistons and so about the pressures evolution on different point of the system. The primary data file was processed in Microsoft Excel, and the resulted diagrams are presented, like example, in Figure 6 and Figure

4 Pressure [bar] Time [ms] Piston stroke [mm] Generator pressure Motor pressure-loaded stroke Motor pressure-idling stroke Generator position Motor position Motor piston stoke Figure 6. Pressures, motor piston stroke, rotational speeds diagram, for delta interconnection configuration at: static pressure 4 bar, generator piston stroke 1 mm and rotational speed 1 rot / s Pressure [bar] Time [ms] Piston stroke [mm] Generator pressure Motor pressure-loaded stroke Motor pressure-idling stroke Generator position Motor position Motor piston stoke Figure 7. Pressures, motor piston stroke, rotational speeds diagram for star interconnection configuration at: static pressure 4 bar, generator piston stroke 12 mm and rotational speed 1 rot/s As the Figure 6 and Figure 7 shows, the diagrams contain complex information regarding the pressures at the generator and the both sides of motor piston, motor piston stroke and so the positions of the generator and motor pistons. The rotational speeds of the generator and the motor are not directly present, but they can be calculated using the number of position peaks in time. In fact every position peak indicates a complete rotation of the generator and the motor shaft. Also for the generator the position peaks indicate the minimum stroke of a selected piston. In the case of the motor, do to the construction dimensions, the rotational speed will be lower than at the generator. If taking account that the generator position peak and the lower peak of the motor piston stroke indicates the minimum value of alternating flow and considering that they have an evolution in time, we can find the alteration of phase angle between the alternative pressure and flow in both cases, for the generator and for the motor, which is important if we consider that the frictional forces, the inertia and the compressibility of the fluid mass, working together, can impose a separate influence for the system. Using the primary diagrams and data files was obtained many other diagrams in which can be observed directly or indirectly the evolutions of different measured parameters. This way can be founded the functioning limits of the studied system. The hydraulic motor was tested on load and idling functioning for the two type of interconnection configurations, star and delta. Figure 8 present for example the pressures and motor pistons stroke evolution for the delta configuration. The dynamic comportment of the system is characterized by that type of diagrams. 368

5 Pressre [bar] Rotational speed [rot/s] Motor piston stroke [mm] p generator p motor-advance p motor-retraction Motor piston stroke Figure 8. Evolutions of pressures, motor piston stroke - rotational speeds, for delta interconnection configuration at: static pressure 4 bar, generator piston stroke 12 mm Pressure [bar] Torque [Nm] Motor piston stroke [mm] p generator p motor-advance p motor-retraction Motor piston stroke Figure 9. Evolutions of pressures, motor piston stroke - torque, for star interconnection configuration at: static pressure 25 bar, generator piston stroke 12 mm and rotational speed 1 rot/s Pressure [bar] Torque [Nm] Motor piston stroke [mm] p generator p motor-advance p motor-retraction Motor piston stroke Figure 1. Evolutions of pressures, motor piston stroke - torque, for delta interconnection configuration at: static pressure 25 bar, generator piston stroke 1 mm and rotational speed 5 rot/s 369

6 2 Phase alteration p-q [degree] Rotational speed [rot/s] Static pressure 15 bar Static pressure 25 bar Figure 11. Phase alteration between motor alternating pressure and flow, for star interconnection configuration at: generator piston stroke 7 mm and rotational speed 1 rot / s On load functioning is realized using the braking device presented in Figure 5. This way the output shaft of the motor is loaded at different values. Figure 9 and Figure 1 present "on load" diagrams with different measured parameters, and by varying the initial conditions, rotational speed and piston strokes of the generator and the loaded static pressure is obtained a complete image on the limits of the designed motor and so for the system. During the system analysis was obtained the diagrams regarding the alterations of phase angle between the alternating pressure and flow. One of these is presented in Figure 11. Analyzing the obtained diagrams, on load and so on idling conditions, we can conclude that on the generator the phase alteration is always negative, indicating a strong inductive influence, but for the motor, depending on the initial conditions and interconnection configuration, the phase alteration can be positive or negative, which means inductive or capacitive influence. 4. CONCLUSIONS The paper presents the interconnection possibilities for the working volumes of the alternating hydraulic motor with alternating flow and pressure energy generator. Within these systems, the active stroke of the pistons, is produced by the pressurized fluid flow from the generator, while, for the retraction stroke there is necessary a supplementary connection to a pressure generator, working in opposite phase with respect to the first one, which means that the pistons can be interconnected in a star or delta configuration. Also the paper presents some of the experimental data obtained as a result of testing of the designed hydraulic motor. REFERENCES 1. Constantinescu G. (1985) Theory of sonics (in Romanian). Romanian Academy, Bucureşti 2. Pop I. I., Marcu I. L., Khader M., Denes Pop I. (1999) Conventional hydraulics. U. T. Pres, Cluj-Napoca 3. Pop I. I., Khader M., Marcu I. L., Denes Pop I. (1999) Modern hydraulics. Pneumatics. U. T. Pres, Cluj- Napoca 4. Pop I. I. (24) New approaches and contributions regarding sonic transmissions. Manuscript. 37