Elsevier

Ocean Engineering

Volume 104, 1 August 2015, Pages 168-184
Ocean Engineering

Numerical and experimental investigation on torque characteristics of seawater hydraulic axial piston motor for underwater tool system

https://doi.org/10.1016/j.oceaneng.2015.05.003Get rights and content

Highlights

  • An integrated torque model including the effect of a dynamic pressure.

  • The effect of pre-compression angle, friction coefficient, and clearances.

  • The experiment verification on the pre-compression angle has been conducted.

Abstract

Seawater hydraulic axial piston motor is an important and elemental component in underwater tool system. The torque characteristics for a swash-plate-type seawater hydraulic axial piston motor is investigated, and an integrated torque model for the motor with symmetrical pre-compression angles has been developed, which consists of a torque sub-model and a dynamic pressure sub-model. Numerical simulations have been carried out to examine the effects of (a) pre-compression angle, (b) relief-groove obliquity, (c) motor speed, (d) piston chamber dead volume, (e) friction on the dynamic pressure and the output torque characteristics. The results indicate that the pre-compression angle, the friction coefficient, and the clearance between cylinder bore/piston have significant impact on the torque characteristics. The test verification has been undertaken with a five piston water hydraulic motor. This research contributes to the mechanism of output-torque fluctuation in a swash-plate-type seawater hydraulic axial piston motor, as well as the investigation of the torque transition phenomenon owing to the pre-compression angle. The research has laid the foundation for the development and improvement of the seawater hydraulic axial piston motor in underwater tool system.

Introduction

Underwater tool system is extensively applied in the sea salvage, marine resource investigation and marine structures or sea defense projects. The underwater tool system driven by seawater hydraulics has many advantages compared with hand-operated tool, electric power tool, pneumatic tool, oil hydraulic tool system, including non-flammability, low operating cost, and low pollution potential to marine environment. Moreover, the seawater hydraulic tool system has the function of pressure self-compensation, which can be designed into open system (Liu et al., 2011, Himmler, 1969). An underwater tool system driven by seawater hydraulics is illustrated in Fig. 1, which is employed to grind the hulls and underwater structures (Nie et al., 2004).

Seawater hydraulic axial piston motor (SAPM) is characterized by the higher volumetric efficiency and lower pv values of the friction pairs in comparison with hydraulic gear and vane motors (Yin et al., 2013, Lim et al., 2003, Yang et al., 2013), which is the main type applied to rotational actuator in the underwater tool system. Output torque is one of the primary performance parameters in SAPM. Because of different physicochemical properties of raw water in comparison with mineral oil, the output torque of the SAPM would be different from the mineral oil one.

Previously, several researchers studied the effect of multiple factors on the dynamic pressure and torque of oil piston pumps/motors. Himmler (1969) presented experimental studies of the low speed-motion for different kinds of hydraulic axial piston motor (HAPM). It was concluded that the static friction in axial piston motor was high, and that the leakage between piston and cylinder had an important effect on the low speed behavior and torque characteristic of HAPM. However, it was not clear from this study whether the leakage increased the effects of static/kinetic friction and was stable at low speed. Hibi and Ichikawa (1975) developed a mathematical model of hydraulic motor to study the friction and torque characteristics in the entire operating process, i.e. from start to maximum speed. Dsagupta et al. (1996) studied the steady state performance of an orbital-rotor, low-speed, and high-torque hydraulic radial piston motor. Guo and Wang (1996) had made an analysis and solving method of pressure inside piston chamber of oil pump when the piston was at transition zone of pre-expansion and pre-compression, respectively. It was proven through simulation that the piston pressure at transition zone was affected by the swashplate angle. Tan et al. (1999) analyzed the transient cylinder pressure in the radial piston hydraulic motors. They established the mathematical models for instantaneous pressure and got the simulation results that distribution overlap of motors must be strictly controlled. Meikandan et al., 1990, Meikandan et al., 1994 analyzed the effects of the tapered piston as well as the friction between piston and cylinder bore on the volumetric efficiency and torque characteristic of HAPM. Sadashivappa et al. (1996) investigated theoretically and experimentally the effects of piston-form deviations on the mechanical and volumetric efficiency of HAPM, through considering the viscous friction and the piston profiles. This study indicated that friction torque of the motor with three-lobe pistons was smaller than that with cylindrical piston. Ivantysynova et al. (2002) investigated the swash plate moment of swash plate axial piston machines through the computer aided design tool CASPAR, analyzed the influence of the valve plate design and the instantaneous pressure in the displacement chamber on swash plate torque. Ke et al. (2006) established a mathematical model of hydraulic motor’s efficiency, analyzed the influence of back pressure on hydraulic motor’s efficiency by numerical simulation and concluded that the back pressure could result in the efficiency reduction, but did not give further analysis of the impact of the back pressure on hydraulic motor’s output speed and torque. Seeniraj and Ivantysynova (2006) studied the effect of valve plate design on flow ripple, oscillating forces and volumetric efficiency. Simulation results revealed that the pressurization and decompression inside the displacement chamber directly related to the flow ripple, forces and torques applied on swash plate. The impact of various valve plate design parameters such as pre-compression grooves, cross port, indexing and additional pre-compression volume were presented by means of the computational tool CASPAR. Bapiraju (2000) developed a torque model of swash-plate-type HAPM taking into account the effects of the piston dynamics and the valve-plate geometry. In this research, the stick-slip friction model was used to numerically simulate the friction effect at the piston-cylinder bore interface. The low-speed characteristics were analyzed in time domain and the phase plane for stability and limit-cycling type of behavior. The limit cycle of the stick-slip behavior on the phase plane was examined, indicating that a chaotic drift was attributed to the variation in friction torque due to piston harmonics. It was the piston harmonics that caused an uncertainty in the motor torque during consecutive stick-slip cycles for the same angular position. The magnitude or the area of the cycle related to the stick zones and kinetic friction pattern would be of benefit to the estimate of friction parameters for HAPM. However, the developed model was based on two theoretical assumptions: (a) the hydraulic fluid inside the piston chamber is switched between high and low pressures at the top dead center (TDC, the point where the piston has the maximum length in the cylinder bore) and the bottom dead center (BDC, the point where the piston has the minimum length in the cylinder bore) of the valve-plate, and (b) the effects of the leakage and fluidic compressibility could be negligible. Bergada et al. (2012) provided a model of temporal pressure in each piston/cylinder chamber and the temporal leakage in all pump clearances. A test rig applicable to measure the dynamic pressure inside a piston chamber was built. The comparison between experimental and simulated results was very good, giving confidence to the model presented.

Although a few prototypes of water hydraulic axial piston pumps were developed, such as University of Hull and Fenner Company in UK (Dsagupta et al., 1996, Brookes et al., 1995), Danfoss A/S in Denmark, Tampere University of Technology and Hytar Oy in Finland (Terävä et al., 1995, Pohls et al., 1999), Delaware University in US (Hicks et al., 1986) and KAYABA and Komatsu Companies in Japan (Yoshinada et al., 1991), little previous study was reported on water hydraulic axial piston motor and corresponding torque characteristics. Chen et al. (2006) developed a model consisting of three masses and 14 DOF to analyze the dynamic vibration of a SAPM. The numerical simulation analysis of the dynamic response of the model due to pressure pulsation was presented and compared with experimental results. A series of the dynamic vibration characteristics of the water hydraulic piston motor were studied by the numerical simulation. It was effective for the model to simulate the vibration signal of the casing in the hydraulic motor. The waveform and frequency of the simulated signal was similar to the experimental signal. To explore the effects of piston dynamics, and output torque characteristics, Nie et al. (2009) established a torque model for the swash-plate type SAPM, which mainly considered the effects of motor speed and pre-compression angle of valve-plate without experimental verification.

As the extension of torque model (Nie et al., 2009), the integrated model is developed in this research, which will tackle the effects of (a) piston dynamics, (b) friction and clearance between piston and cylinder bore, (c) dynamic pressure inside piston chamber, (d) compressibility of hydraulic fluid, and (e) pre-compression angle of valve-plate. The detailed effects of these impact factors on the instantaneous torque will be investigated through extensive sensitivity analyses.

Section snippets

Statement of problems

The schematic diagram of the SAPM is shown in Fig. 2, and the piston forces are shown in Fig. 3. The motor is consisted of five pistons within a cylinder block. The cylinder block is held tightly against the valve-plate. A thin water-lubricating film separates the cylinder block and the valve-plate. The pistons protrude out of the right end of the cylinder block, and end in a ball and socket joint with slippers. The slippers are held against the face of the swash-plate by a retainer and a piece

Simulation and analysis

The parameters related to this simulation are listed in Table 1. Numerical simulations for the dynamic pressure inside piston chamber and the output torque have been carried out by solving the integrated model with help of MATLAB software package.

Test verification

Based on the previous research, an optimized SAPM is fabricated and the torque characteristics test is undertaken with the previous motor and the optimized motor on the water hydraulic system test rig. The test rig is designed for the study of water hydraulic components and system, with the installed power of 75 kW, rated pressure of 14 MPa and speed ranging from 0 to 1500 r/min (as shown in Fig. 15). Tested motor 16 is driven by high pressure water from water pump 5, and the system pressure could

Discussions

  • (1)

    As shown in Fig. 8a and b, when the clearance between the valve-plate and cylinder block is not considered under condition of small relief-groove obliquity on the valve-plate, the dynamic pressure (pc) at quadrant I and quadrant II would decrease to be lower than the fluidic vapor pressure (near to the absolute negative pressure). Obviously, this is impossible and not physically acceptable. Actually, the clearance between the valve plate and cylinder block does exist and would lead to leaking

Conclusion remarks

  • (1)

    An integrated torque model of an axial piston motor with symmetrical pre-compression angles has been developed, which consists of a torque sub-model (including the friction effect) and a dynamic pressure sub-model. The integrated torque model has taken into account the effects of the dynamic pressure inside the piston chamber, the piston friction, the fluidic compressibility, the pre-compression angle and other related parameters.

  • (2)

    Numerical simulation have been carried out to examine the effects

Acknowledgments

The authors would like to thank the National High-tech R&D (863) Program (no. 2012AA091103), National Natural Science Foundations of China (no. 51375018), The Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions (CIT&TCD 20130316) and Doctoral Fund of Innovation of Beijing University of Technology (YB201401) for their funding for this research. The authors would like to thank the anonymous reviewers for their insightful comments and suggestions that were

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