Cam-follower Contact Research Articles

Analytical, Numerical and Experimental Analysis of a Positive Displacement Cam Mechanism—A Case Study

Cam mechanisms, covering a large structural variety, are widely used in machinery, mainly as components of automated systems. Their functioning behavior is affected by negative dynamic phenomena determined by specific high velocities and acceleration rates. Within the various types of research on the dynamic behavior of cam mechanisms, this study addresses the need to clarify the influence of geometrical parameters and technological conditions on some indicators of the jump phenomenon in contact loss for a cam-follower mechanism. This particularly developed case study referred to a mechanism with a profiled grooved disk cam and oscillating follower. To highlight the influence of the cam-follower contact elasticity on the jump phenomenon, two dynamic models were developed: one considering rigid elements in contact and the second considering elastic cam-follower contact. The models were tested within a virtually simulated experiment, and the numerical simulation results evidenced the influence of input factors like the applied load on the mechanism, the clearance in the cam-follower kinematic pair, and the rotational speed of the cam, and the inertia moment was reduced to the follower on some indicators of the jump phenomenon. Validation FEA and experiments were performed, proving the reliable appropriateness of the dynamic model based on elastic cam-follower contact.

Tribological parameters analysis of cam and follower pair used in IC engine using ANSYS

The cam and follower pair play an essential role in the valve train mechanism in IC engines. An IC engine has a specific form of contact condition called cam and follower contact. The tribological parameters related to this contact are vital for engine performance. In this paper, the cam and follower pair are analyzed, and improvements to the traditional material used for making the cam and follower are suggested. A 3D geometry of the disc type cam and spherical follower used in a typical IC engine is designed using Solidworks software, and Finite Element Analysis (FEA) of the cam and follower assembly is done using the CAE software ANSYS Mechanical. The materials taken for this analysis are structural steel and grey cast iron. We have done analyses of two of the most important tribology parameters: contact pressure and Hertzian contact stress. The maximum value of contact pressure and Hertzian contact stress is calculated for both types of material, and the results are presented and compared in tabular form and using graphical plots. The results showed that the contact pressure, Hertzian contact stress increase linearly with each other for both type of materials. Also, the maximum values of Hertzian contact stress and contact pressure were lower for grey cast iron material. So, it is a preferable substitute to structural steel for making the cam and follower pair of a motorcycle IC engine. A good agreement of results showed that our model provided a reliable prediction of the tribological characteristics of the cam follower contact.

Triboinformatic modeling of the friction force and friction coefficient in a cam-follower contact using machine learning algorithms

In this study, the coefficient of friction and friction force in a cam follower mechanism were estimated using modern machine learning (ML) algorithms. Three different ML algorithms were implemented to the experimental tribological data to estimate the change in the friction coefficient and friction force depending on the cam rotation angle: Artificial Neural Network (ANN), Support Vector Machine (SVM), and Gaussian process regression (GPR). We demonstrated through performance analysis that ML-based models can effectively estimate the change in the friction coefficient and friction force. We also comparatively evaluated the performance of ML-based models. The FF-ANN model estimated the friction force with the best performance while the FC-GPR model was more successful in estimating the coefficient of friction. The models show different estimation performances at different preloads and different cam rotation speeds.

Contact Force Measurements in Cam and Follower Lubricated Contacts

Cam-follower contacts are characterized by continuous changes of operating parameters such as speed, load and geometry, so that both numerical simulations and experimental measurements are very complex. An experimental apparatus has been specifically designed and realized to perform tests with cam–follower pairs. The apparatus allows measurements of contact forces with a custom-made dynamometer and of lubricant film thickness and shape with optical interferometry. After an introductory review of experimental works on cam-follower pairs mainly related to force measurements, the test rig used for the experimental work reported in the paper is briefly described. Some trends of all components of the contact forces measured during the rotation of a circular eccentric cam and an engine spline cam are presented. Tests have been performed at different rotational speeds and preloads. The friction trends can be associated to mixed and boundary lubrication regimes. Some unattended friction peaks are found in tests with the spline cam and possible explanations are given.

Film Thickness and Shape Evaluation in a Cam-Follower Line Contact with Digital Image Processing

Film thickness is the most important parameter of a lubricated contact. Its evaluation in a cam-follower contact is not easy due to the continuous variations of speed, load and geometry during the camshaft rotation. In this work, experimental apparatus with a system for film thickness and shape estimation using optical interferometry, is described. The basic principles of the interferometric techniques and the color spaces used to describe the color components of the fringes of the interference images are reported. Programs for calibration and image analysis, previously developed for point contacts, have been improved and specifically modified for line contacts. The essential steps of the calibration procedure are illustrated. Some experimental interference images obtained with both Hertzian and elastohydrodynamic lubricated cam-follower line contacts are analyzed. The results show program is capable of being used in very different conditions. The methodology developed seems to be promising for a quasi-automatic analysis of large numbers of interference images recorded during camshaft rotation.

DESIGN AND ANALYSIS OF CONSTANT-BREADTH CAM MECHANISM WITH OSCILLATING FLAT-FACED FOLLOWER

A simple yet comprehensive method is presented for the design and analysis of a constant-breadth cam mechanism with an oscillating flat-faced follower. In the proposed approach, the kinematic characteristics of the cam mechanism are first derived. The cam profile is then designed using homogenous coordinate transformation and conjugate surface theory. Moreover, the sliding velocity at the cam-follower contact points is determined. Finally, the pressure angle of the constant-breadth cam mechanism and the principal curvatures of the cam are analyzed. The validity of the proposed design methodology is verified by means of motion simulations performed using CAD software.

Transient Thermal Elastohydrodynamic Modeling of Cam–Follower Systems: Understanding Performance

ABSTRACTThis article deals with the lubrication of cam–follower contacts in automobile racing applications. Time-dependent thermal elastohydrodynamic line contact simulations are performed to analyze the contact performance achieved with a shear-thinning lubricant under highly dynamic conditions. Comparisons between different simulations are used to quantify the respective influence of shear thinning, thermal softening, and transient effects on friction and film thickness. Furthermore, this article highlights the formation and transport of a transient dimple responsible for an increase in lift close to the conditions where reversals of entrainment occur. Temperature distributions across the film thickness and pressure variations are reported to discuss the underlying phenomena.

Dynamic analysis of a car engine valve train system

In this paper, a multibody model of a car engine valve train system was developed, by using LMS Virtual.Lab software, in order to analyse its resonant vibrational behaviour. The model complexity is the result of a compromise between the need to obtain accurate results (with acceptable run times) and the requirement of an easy integration of subcomponent models into a virtual assembly. The cam-follower contact was modelled using appropriate tools of the adopted code (Generator Cam, Cam Contact). Model validation was realised by comparing the kinematic laws of the valve motion, obtained from the numerical simulation, against those obtained from the experimental tests performed by FCA Group. Then, the dynamics of the valve train system was analysed, applying a ramp to the crankshaft with a variable engine speed (1,000 to 6,000 rpm) and considering the motion unsmoothness deriving from the inertia and combustion pressure loads. The camshaft is considered rigidly connected to the crankshaft by a mechanism with a transmission ratio equal to 0.5. Such analyses allow to assess the valve bounce, the disengagement phenomena of the cam-follower system, the resultant forces acting on the camshaft bearings, and the resisting torque on the camshaft.

Cam mechanisms based on a double roller translating follower of negative radius

Constant-breadth cam mechanisms are characterized by the fact that the closure of the cam-follower contact is guaranteed thanks to the geometry and, therefore, auxiliary elements as springs are not necessary. On the other hand, cam mechanisms with a negative radius roller follower allow designing simple machines exerting remarkably high forces when the space is restricted. This work proposes a new constant-breadth cam mechanism with a double roller translating follower of negative radius. The cam profile is designed with an optimizing method based on Bézier curves.

COSRING-LUJET, Integrated New Concept in Automotive I.C. Engines for a Better Lubrication

The COSRING-LUJET is a new concept for integrated solution to improve the lubrication regime in internal combustion engines. Introducing a conical shape for the peripheral surface of the rings, the authors analyze the conditions for the lubrication regime. Under this new concept, entitled COSRING, has developed a method for determining the transversal profile of the first and the second compression ring in order to obtain a better lubrication conditions for the piston ring – cylinder line assembly. On the other hand, the authors analyze the main factors affecting the cam-follower contact conditions, emphasizing the influence of the lubrication regime conditions over the couple wear reduction. The LUJET concept, proposed and studied by the authors, is an original solution for the improvement of the lubrication regime and engine life by using additional oil jets directed over the contact area.

Radius of curvature and sliding velocity in constant-breadth cam mechanisms

In constant-breadth cam mechanisms closure of the higher kinematic pairs formed by the bilateral cam-follower contact is guaranteed by the geometry of both cam and follower. A study of the cam profile by means of its radius of curvature and the sliding velocities in the upper pair enables us to predict the correct functioning of the mechanism. This work presents the equations for calculating cam breadth when the translating follower is eccentric with an inclination, the radius of curvature of its profile and the sliding velocities of constant-breadth cam mechanisms with translating and oscillating followers. This study also analyses the influence of the angle of inclination and the offset of the flat-faced translating followers on the size of the cam and the kinematics of the mechanism. Numerical examples are given of constant-breadth cams obtained for distinct values of the mentioned parameters. Additionally, this paper describes the redesign of a cam of a conventional sewing machine and the new cam prototype, with a continuity of an order higher than the original profile, is included.

Experimental study on circular eccentric cam–follower pairs

Experimental verifications of cam–follower contacts are very important owing to the difficulties faced during 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 r/min, and different pre-loads have been investigated. Lubrication regimes ranged from boundary to complete, with most of the tests being 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 as well as the evaluated trends of the friction coefficient are presented in the paper. Some sample optical interference images are also shown. The results furnish encouraging indications about the capabilities of the experimental apparatus.

Ways to improve conditions in mineral oil lubrication of the internal combustion engines

AbstractThe paper analyses some phenomena affecting the cam-follower contact conditions, highlights some detrimental influences over the lubrication regime in this contact. The analysis of the theoretical model revealed the significant influence of thermal and starvation effects on the reduction of film thickness. To avoid these negative phenomena and in order to improve the lubrication regime we propose an original technical solution by using additional oil feed with oil jets, directed over the contact area.

Investigation on cam–follower lubricated contacts

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 complexity of the phenomena occurring in the camshaft systems makes experimental verifications very important. In this study, an already existing versatile experimental apparatus for the investigation 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 programme 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.

Synthesis and analysis of coupler curves with combined planar cam follower mechanisms

Cam and follower mechanisms are widely used to convert a rotary input motion into a controlled reciprocating or oscillating motion as output in machines or robots. As this mechanism has an ability to provide unlimited variety of output motions. Many works are done on the synthesis of coupler curves or path generation using four bar mechanism. The present work investigates the alternative way of dealing with the path generation problems of industrial application by using cam mechanisms. Proposed a new mechanism which comprises four bar and cam follower mechanism, these mechanisms are combined together to obtain a single-input combined cam mechanism (CCM). Dimensional synthesis has been carried out by guiding the coupler point along predefined path (ellipse or straight line) of profile cutting machine. One of the objectives was to compare the path of coupler in four bar and CCM. Further, kinematic simulation of both mechanisms was performed to estimate the error and validate the proposed methodology. Results show that coupler point follows same path as ellipse or straight line profile in both mechanisms. Proposed CCM successfully applied to the complex path generation problems of profile cutting machine like square, circle and figure eight profiles. A method of kinematic analysis of proposed mechanism was also discussed. Finally, dynamic stability and separation of cam follower contact was simulated by using Matlab Simulink tool. Results show that proposed CCM was found stable from kinematic and dynamic point of view. International Journal of Engineering, Science and Technology, Vol. 2, No. 6, 2010, pp. 231-243

Scuffing detection of TU3 cam–follower contacts by electrostatic charge condition monitoring

The increasing costs associated with lubricant development and qualification has driven the need for condition monitoring techniques to be deployed on test engines to maximise information gained from expensive testing programmes. This paper discusses the results from a motorised TU3 engine with electrostatic sensors focused on the cams. System characterisation tests and an oil starvation test were used to decouple charge mechanisms associated with a lubricated wear test, accelerated through the use of carbon black. Cross-correlation of various charge signal processing techniques, scanning electron microscopy and profilometry revealed that tribocharging dominated during running-in/mild wear and contact potential difference (CPD) dominated during the progression of severe adhesive wear. Tribocharging (the charge generated by a low conductivity fluid) has been shown to be affected by oil temperature, cam rotation speed and the presence of charged species within the lubricant. Contact potential differences was principally generated by the work function difference between oxidised and nascent regions associated with adhesive wear on the cam surface. Electrostatic monitoring which is sensitive to lubricant chemistry and wear, and can be implemented in an industry standard engine, has great potential for the lubricant industry.

Combined multi-body dynamics and experimental investigation for determination of the cam-flat tappet contact condition

The paper investigates the tribological contact conditions between a polynomial automotive cam and a flat follower. A multi-body model of the system is presented to take into account the complex tappet motions. A set of such models is presented in order to predict the cam-tappet friction force, the tappet-tappet bore friction force and the resulting tappet spin. The tribological conditions giving rise to these kinetic actions include the elastohydrodynamic regime of lubrication in the concentrated cam-follower contact and a mix of hydrodynamic and boundary friction action in the tappet-tappet bore contact. While boundary friction dominates the tappet-tappet bore friction at low engine speeds, for high engine speeds the boundary friction dominates the closing event of the cam, and hydrodynamic and mixed lubrication dominate the opening event of the cam. The simplified friction models are experimentally validated on a single-cylinder diesel engine. The measuring techniques are based on a redesigned engine tappet equipped with four strain gauge bridges.

Mid-life scuffing failure in automotive cam-follower contacts

There are several practically important engineering systems that fail by scuffing long after the initial running-in has been completed. A common feature of these systems is repeated contact between the same points on the mating surfaces. The processes leading up to such mid-life scuffing failures have been examined by monitoring the development of cam follower surface roughness and wear at regular intervals during a series of valve train wear tests in a fired engine. By the application of both statistical and numerical models for the elastic contact of rough surfaces, the following stages in the scuffing process have been identified: (a) surface roughening in the mild-wear regime, which progressively increased maximum asperity contact pressures until (b) the elastic shakedown limit was exceeded, causing plastic deformation wear, accelerated roughening and enlargement of valleys, leading eventually to (c) a transition to high rates of wear, probably resulting from hydrodynamic pressure loss and oil-film collapse.

Simulation of the mild wear in a cam-follower contact with follower rotation

Mild wear may have damaging effects on contacting components, when the material removal distorts component geometry. Surface pressures can then be redistributed in an unfavourable way which increases the probability for surface fatigue. Phenomena like this have been observed in an ordinary automotive cam-follower contact. The purpose of this work is to derive a simulation model for the mild wear in a cam-follower contact with follower rotation. The mild wear in such a contact is simulated using the principle of single point observation. The simulation model is based on a modified Archard's wear equation. After each simulation step the pressures are recalculated using the topographically changed surfaces. Three cases are studied: one where only follower wear is considered, one where only the cam wear is simulated and finally the case where both and cam follower wear is simulated. An FEM analysis of the follower was used to verify the infinite half plane assumption in the pressure calculations. The present work highlights the importance of including follower rotation in the wear simulation and the use of the single point observation method in the derivation of a wear simulation model. The results show that the case where only the cam is worn gives the lowest contact pressures. The case where only follower wear is considered is the most unfavourable when it comes to contact pressures and wear.

Simulating follower wear in a cam—follower contact

Mild wear in a rolling-sliding contact may gradually worsen the contact conditions. The probability for surface fatigue will then increase due to changes in the surface topography. This phenomenon has been observed for cam-follower contacts in automotive engines. A simulation model of the wear of a follower based on the principal of single point observation has been developed. The wear is simulated using a modified version of Archard's wear equation. The simulation is carried out in steps, recalculating the pressures as the surface topography gradually changes. The results show good agreement with corresponding worn surfaces. It can be concluded that the simulation method presented here, using a modified Archard's wear equation, can be used to simulate the mild wear in a rolling-sliding contact. This work highlights the importance of including follower rotation in the wear simulation and the use of the single point observation method in the derivation of a wear simulation model.