Geometrical imperfections on pistons cause an asymmetric pressure distribution in the clearance between the piston and cylinder bore. Due to this, the piston attains different eccentricity positions during a stroke. The eccentricity of the piston affects the performance of the cylinder by influencing the frictional and leakage aspects. A compact mechatronic test rig is designed and fabricated to measure the piston eccentricity and friction in a dynamic condition. Pistons of defined geometric profiles such as elliptic and three-lobe are fabricated using a machining center. These pistons have been introduced into the test rig. The eccentricity and dynamic friction tests are conducted at various operating conditions and the results are presented and analyzed.

Makaram Singaperumal

K. Narayanasamy

Engine cylinders

Force measurement

Friction

Leakage (fluid)

Pressure distribution

HYDRAULIC CYLINDERS

PISTON ECCENTRICITY

Engine pistons

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Piston eccentricity and friction force measurement in a hydraulic cylinder in dynamic conditions considering the form deviations on a piston

Mechatronics

Friction in servo hydraulic assemblies reduces the response characteristics of the system. The friction is influenced by various factors including the geometry (form and surface errors) of the sliding surfaces. In this work, functionally significant 3D surface parameters from the Birmingham parameters are investigated for reduced friction. A 3D surface modelling approach is presented using random process modelling as the basis. An exponential decay areal autocorrelation function is used to model the grinding and honing processes which are commonly employed for the manufacture of the hydraulic assemblies. Honed surface is modelled with the crosshatches of appropriate angle. Method of surface modelling is validated using the data obtained through measurements on a practical surface. Different surface maps with varying surface parameters of the ground and honed surfaces are generated. The fluid continuum gap geometries of the hydraulic assemblies are modelled using these surface maps as envelopes. Pressure distribution, velocity and viscous friction force are used as measurands of the frictional characteristics. Using computational fluid dynamics (CFD) approach, these measurands are evaluated for different functionally significant Birmingham parameters. Based on further analysis, negative skewness, lower kurtosis values, higher valley fluid retention index were found to have lower frictional characteristics. © 2008 Elsevier Inc. All rights reserved.

Precision Engineering

Modelling of fluid continuum considering 3D surface parameters in hydraulic assemblies

Axial piston motors rely on a close fit of piston to bore to minimise leakage past the piston due to axial pressure drop. Machining imperfections in the cylinder bore and the piston change the clearance between them, affecting the performance of the motor. The effect of machining imperfections like out-of-roundness and taper in the piston on the mechanical and volumetric efficiency of the motor, in the speed range where the viscous friction is dominant, are studied. Experiments to measure torque and leakage flow are conducted on a fixed displacement swash plate type axial piston hydraulic motor and results are presented. Copyright © 1996 Elsevier Science Ltd.

On the efficiency of the axial piston motor considering piston form deviations

Use of seals on the piston surface of servo hydraulic actuators causes, apart from excessive wear, positional inaccuracies arising out of large mechanical friction due to physical contact. In order to improve their performance, modern servo hydraulic actuators use pistons with tapered surfaces. When such pistons move within the cylinder there is a chance of generating sufficient oil pressure to lift the piston owing to hydrodynamic action. Theoretical study on three types of such pistons was reported earlier. In this paper, experimental work carried out on those tapered pistons is presented. A new test-rig has been developed to test the actuators, and the test results confirm the main findings of the theoretical study. © 1994.

Wear

Experimental study of friction in hydraulic actuators with sealless pistons

In a high speed hydraulic actuator the usage of seals on the piston surface causes excessive wear on the seals and positional inaccuracies owing to coulomb friction. Hence sealless pistons with sloping surfaces have been tried by some manufacturers of such actuators. Here an attempt is made to analyse systematically the three types of profiles commonly considered for high speed actuators, using Reynolds' differential equation. Analyses are made using an analytical method for one-dimensional flow and using the finite element method for two-dimensional flow. The analyses reveal that single tapered pistons have certain limitations and that double tapered pistons can function successfully under different conditions in hydraulic actuators. It is also shown that friction in these types of pistons is much less than in conventional pistons with seals. © 1990.

Journal	Mechatronics
ISSN	09574158
Open Access	No