1,720,972 research outputs found
Experimental study on circular eccentric cam-follower pairs
Full text linkExperimental verifications of cam-follower contacts are very important because of the difficulties for a reliable simulation due to the continuous variation of load, speed and geometry of the lubricated contact. Some experiments have been carried out with a new apparatus, specifically designed and realised for investigation on cam-follower and gear teeth contacts, in order to test its capability to measure film thickness and contact forces. Circular eccentric cams have been used because they feature lower transient effects and comparison of the results with the theoretical/numerical ones is easier. The tests have been performed using cams with two different eccentricities and surface roughness, and two different followers, one made of steel and one made of glass.
The behaviour of the cam-follower contacts at several different rotational speeds, ranging from 50 to 500 rpm, and different pre-loads have been investigated. Lubrication regimes ranged from boundary to complete, being most of the tests performed under mixed lubrication conditions. Localised wear has occurred during some tests. Data of all contact force and moment components as well as of the cam shaft driving torque have been acquired at high acquisition frequency. Some methodologies for numerical data elaboration have been identified. Optical interference images have been correctly recorded at the desired frequency. The trends of the normal and friction forces measured in the different tests are presented in the paper, as well as the evaluated trends of the friction coefficient. Some sample optical interference images are also shown. The results furnish encouraging indications about the capabilities of the experimental apparatus
Investigation on plain journal bearings for severe working conditions
No full textIn this paper a theoretical and experimental work for design of plain journal bearing able to work up to severe conditions is reported.
The mathematical model and the numerical methods on which a purposely developed computer program is based are firstly described. The program is aimed to the evaluation of the behaviour of hydrodynamic plain journal bearings under heavy static loads, considering the elastic deformation of the bearing members, geometrical errors such as the axis misalignment and thermal effects.
The experimental apparatus designed and set up for testing plain bearings in several working conditions, by varying speed, load and oil supply up to extremely critical situations, is then briefly described.
Theoretical and experimental results obtained at different load, speed and oil flow rate conditions are finally compared showing a good agreement
Experimental study of engine cam-followers
No full textThe cam-follower pair is a very complex lubricated contact because its continuous variation of load, speed and radius of curvature. Experimental verification are necessary but very difficult to perform. After a literature review of the existing test rigs for cam-follower simulation, the main aspects of a new versatile apparatus are presented. Several design variations are presented, each one with its advantages and drawbacks. The final project will take into account some of the presented design solutions and the results of dynamic simulations of the rigs currently under elaboration
Wear and elastohydrodynamic lubrication studies of cams and followers
No full textThe concentrated non-conformal contact between the cam and the follower is one of the most severe working tribological components in the internal combustion engine. Due to the continuous variation of load, speed and geometry, this contact is very difficult to be investigated.
This work is mainly devoted to review the wear and elastohydrodynamic film thickness studies related to this important engine mechanism and is divided into two parts.
In the first part a review is made of theoretical/numerical studies addressed to predict the film thickness, pressure distribution and their relations with the most common surface failures as pitting and scuffing.
The second part is committed to show the experimental efforts that have been carried out to estimate the real film thickness and the force friction in order to improve the durability of mating cam/follower surfaces under elastohydrodynamic lubricating regimen. A new versatile experimental apparatus under development is also presented
Investigation on cam–follower lubricated contacts
Full text linkAbstract: The Investigation on cam–follower contact is one of the most complex lubricated non-conformal contact due to its continuous variation of load, speed, and geometry. The com-plexity of the phenomena occurring in the camshaft systems makes experimental verifications very important. In this study, an already existing versatile experimental apparatus for the inves-tigation of non-conformal lubricated contacts, able to measure film thickness using the optical interference method and friction force trough a load cell, has been modified in order to test cam– follower contacts. Some tests have been carried out for investigating the behaviour of some fundamental components of the rig. A theoretical/numerical simulation has been performed to investigate the dynamic behaviour of the system and in order to provide some indications for the interpretation of the experimental results. Purposely developed versions of the pro-gramme have been also an important support for the design of a new apparatus specifically addressed to the cam–follower contact with increased potentialities capable of more detailed measurements of film thickness and contact forces. The apparatus is able to reproduce a cam– follower mechanism that uses a rocker as a link device between the cam follower set and the valve
Numerical multilevel investigation for evaluation of pressure distribution in EHL circular contacts from film thickness measurements
No full textIn this paper an analysis of the Elastohydrodynamic lubricated circular contact through a hybrid technique is presented. In particular the attention is focused on the pressure distribution calculation. A versatile code has been developed, able to evaluate the pressure distribution starting from 3-D film thickness maps obtained from the analysis of the interferometric images. The code is developed in C++ and is based on Multigrid Technique. This hybrid technique has a basic advantage with respect to the full numerical approach: the pressure is obtained without making any assumption about the lubricant itself. The main disadvantage of the method is that high resolution of the interferometric images is requested
Hydrostatic lubrication with cryogenic fluids
No full textThe paper presents a computational procedure that can be useful in assessing the main performance parameters (load, flow rate, attitude angle) of hydrostatic journal bearings, without resorting to full numerical computing. The procedure is based on the “lumped resistance method”, which has been extended to take into account turbulence and inertia effects. Comparison with available experimental data shows a pretty reasonable agreement, in spite of the approximations that have been introduced. The procedure has been used to design a number of bearings that have been tested in order to study the possible replacement of rolling bearings in cryogenic turbopumps
Experimental and Theoretical Results on the CRTM Plain Journal Bearings up to Extreme Working Conditions
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