No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Tribo-dynamics analysis of engine small-end bearing under real temperature boundary conditions by a wireless in-situ measuring technology
... Firstly, a more comprehensive tribo-dynamics and bearing temperature prediction model was established with taking into account the impacts of elastic deformation and lubricant rheology for engine big-end bearing system. Secondly, the wireless in-situ temperature measurement equipment developed in our previous work [40] is modified based on the big-end bearing system features. Then, full-size engine tests were performed to measure the internal bearing temperature under actual engine operating conditions. ...
... This hinders the validation of numerical models' accuracy and could be a reason why many researchers' models do not consider bearing temperature behavior. Notably, This study benefits from the author's prior research [40], where a wireless temperature measurement device was developed specifically for small-end bearings. After some modification, this device can now be used to measure the big-end bearing temperature during ignition conditions. ...
... Notably, traditional wired or indirect measurements of bearing temperature have significant limitations. In our previous study, we successfully developed an in-situ wireless temperature measurement device for engine components [40]. In this experiment, it was successfully employed to wirelessly measure the big-end bearing temperature. ...
... Rights reserved. R. Li et al. become an academic term [12,26,37,63,69]. Building a tribo-dynamics model often starts with building a dynamics model. ...
Lubricated translational joints are extensively utilized in power equipment. Due to the presence of clearance, the moving mass exhibits transverse motion within the guide rail in addition to its reciprocating motion. This transverse motion significantly influences the friction, wear, and service life of the friction pair. In this process, multi-physics factors such as fluid lubrication, structural deformation, and frictional heat generation interact with each other, making the tribo-dynamics characteristics very complex. In the current study, a new thermal-fluid-solid coupled method for modeling the tribo-dynamics of translational lubricated joints is presented, and it is applied to the crosshead slider-guide friction pair in marine engines. Research results show that the tribo-dynamics characteristics of the slider predicted by the model is consistent with the experimental ones, the correctness of the model is verified. The frictional heat generation has little effect on the tribo-dynamics characteristics of the crosshead slider under the rated operating conditions. However, the structure deformation induced by the external load intensifies the transverse motion of the crosshead slider. Compared with the model that ignored the deformation, the transverse displacement can be increased by 30%, which indicates that it is necessary to consider the multi-physics coupling effect.
The bushing of connecting rod small end is one of the most prone components to failure in diesel engines. According to the previous study, the oil flowrate and storage of small-end bearing with splash lubrication are both minimal at maximum speed. Thus, the optimization of oil bores was performed using a model based on smooth particle hydrodynamics. By adjusting the angle between the axes of two oil bores to 90 deg, the oil flowrate and storage increase from 0.036 mL/s and 0.04 mL to 0.094 mL/s and 0.045 mL, respectively. A semicolumn baffle above the oil bore away from the piston cooling nozzle further increases them to 3.564 mL/s and 0.8 mL. The optimization greatly enhances the cooling intensity and oil supply stability of small-end bearing, conducing to prevent bushing failures.
In this study, the linear weighting summation method is adopted for the co-optimization of V-shape textured bearings to maximize the load-carrying capacity and minimize the leakage and friction. Optimal parameters including texture angle and depth and ratio of the texture width are identified based on the established numerical model. Moreover, to improve the comprehensive performance, especially leakage reduction, two profile modifications are introduced: micro-slope and micro-step. The results show that the two proposed modifications are effective for improving the comprehensive performance of V-shape textured journal bearings, and optimal values exist for both the modifications. Furthermore, the overall performance of a bearing with micro-step modification is superior to that of a bearing with micro-slope modification, but the bearing with micro-slope modification is more sensitive to leakage. In summary, this study aims to provide theoretical foundation for the multi-objective optimization design of V-shape textured bearings.
For the ring/liner conjunction, well-designed surface texturing has been regarded as a potential means to improve its tribological performance, as well as the application of coating. However, so far most researchers focused on the one of these aspects. In this study, the combined effect of coating and texturing on the performance of ring/liner conjunction is numerically investigated. A thermal mixed lubrication model is presented. The effects of the coating’s thermal and mechanical properties on the tribological performance are studied under the cold and warm engine operating conditions. Along with the increasing coating thickness, the effects of the coating’s thermal properties on friction loss are found to be significant, as well as the effects of the coating’s mechanical properties. It is also found that a soft coating with a lower thermal inertia has a greater ability to reduce the friction loss of the textured conjunction.
h i g h l i g h t s Cylinder liner temperature affects frictional losses. Optimum liner temperature improves energy efficiency and reduces emissions. Liner temperature is hardly affected by viscous shear of lubricant. This implies optimum conditions would be independent of engine speed. a b s t r a c t Despite extensive research into alternative methods, the internal combustion engine is expected to remain as the primary source of vehicular propulsion for the foreseeable future. There are still significant opportunities for improving fuel efficiency, thus directly reducing the harmful emissions. Consequently, mitigation of thermal and frictional losses has gradually become a priority. The piston-cylinder system accounts for the major share of all the losses as well as emissions. Therefore, the need for an integrated approach, particularly of a predictive nature is essential. This paper addresses this issue, particularly the role of cylinder liner temperature, which affects both thermal and frictional performance of the piston-cylinder system. The study focuses on the top compression ring whose critical sealing function makes it a major source of frictional power loss and a critical component in guarding against further blow-by of harmful gasses. Such an integrated approach has not hitherto been reported in literature. The study shows that the cylinder liner temperature is critical in mitigating power loss as well as reducing Hydrocarbon (HC) and Nitrogen Oxide (NOx) emissions from the compression ring – cylinder liner conjunction. The results imply the existence of an optimum range for liner working temperature, independent of engine speed (at least in the studied cases) to minimise frictional losses. Combined with the study of NOx and HC emissions, the control of liner temperature can help to mitigate frictional power loss and reduce emissions.
Several typical and uncommon failure modes in con-rods for internal combustion engines are commented from the stress level viewpoint. The interpretation of the fractures is supported with traditional calculations, with more advanced analytical models, and with Finite Element (FE) predictions. The repertoire of failures in a con-rod is presented by separately addressing the parts composing the con-rod itself, namely the shank, and the small and big ends.
Running conditions for piston pin boss bearing have become very severe due to the high combustion pressure and piston temperature increase over the past ten years. The aim of this paper was to analyze the friction and lubrication characteristic of piston pin boss bearings and a connecting rod small end bearing. This paper provided a comprehensive analysis of piston pin based on a multi-body dynamic model which considers the oil film cavitation and structure deformation. Effects of different lubrication models, pin structures, and thermal deformation on the lubrication were discussed. The lubrication characteristics and performance parameters including oil film pressure distribution, asperity contact pressure, the minimum oil film thickness, the maximum oil film pressure, and friction power loss were listed. The results showed that the minimum oil film thickness was very different and the maximum oil film pressure was nearly the same. A parabola profile of pin bore can reduce the wear to some extent, and a flare profile intensified wear in some places and caused the wear to be concentrated on a smaller area. Reducing the inner diameters will reduce the wear of the pin boss. However, in a realistic design of the pin, avoiding high inertial force of the piston system and satisfying the demand for reliability of the pin, increasing the inner diameters and reliability is a ‘trade off’ problem. A suitable design of the hollow diameter is very important. The results can provide guidance for the design of the pin boss bearing. © 2015, Zhejiang University and Springer-Verlag Berlin Heidelberg.
Presented in the paper is a comprehensive analysis for floating piston pin. It is more challenging because it is a special type of journal bearing where the rotation of the journal is coupled with the friction between the journal and the bearing. In this analysis, the multi-degree freedom mass-conserving mixed-EHD equations are solved to determine the coupled pin rotation and friction. Other bearing characteristics, such as minimum film thickness, pin secondary motions in both connecting-rod small-end bearing and piston pin-boss bearing, power loss etc are also determined. The mechanism for floating pin to have better scuffing resistance is discovered. The theoretical and numerical model is implemented in the GM internal software FLARE (Friction and Lubrication Analysis for Reciprocating Engines).
One of the major problems that the automotive industry faces is reducing friction to increase efficiency. Researchers have shown that 30% of the fuel energy was consumed to overcome the friction forces between the moving parts of any automobile. The interface of the piston pin and pin bore is one of the areas that generate high friction under severe working conditions of high temperature and lack of lubrication. In this research, experimental investigation and theoretical simulation have been carried out to analyze the motion of the floating pin against pin bore. In the experimental study, the focus was on analyzing the floating pin motion by using a bench test rig to simulate the floating pin motion in an internal combustion engine. A motion data acquisition system was developed to capture and record the pin motion. Thousands of images were recorded and later analyzed by a code written by MATLAB. In the simulation, friction and lubrication analysis for reciprocating engine (FLARE) tools were adopted to carry out an elastohydrodynamic (EHD) lubrication analysis of the piston pin/bore interface and simulate the pin motion. The results showed that the motion of the floating pin was significantly affected by applied load and lubrication conditions. The experimental and theoretical results match very well.
Most models of surface contact consider the surface roughness to be on one of the contacting surfaces only. The authors give a general theory of contact between two rough plane surfaces. They show that the important results of the previous models are unaffected: in particular, the load and the area of contact remain almost proportional, independently of the detailed mechanical and geometrical properties of the asperities. Further, a single-rough-surface model can always be found which will predict the same laws as a given two-rough-surface model, although the required model may be unrealistic. It does not seem possible to deduce the asperity shape or deformation mode from the load-compliance curve.
Access to clean, affordable and reliable energy has been a cornerstone of the world's increasing prosperity and economic growth since the beginning of the industrial revolution. Our use of energy in the twenty-first century must also be sustainable. Solar and water-based energy generation, and engineering of microbes to produce biofuels are a few examples of the alternatives. This Perspective puts these opportunities into a larger context by relating them to a number of aspects in the transportation and electricity generation sectors. It also provides a snapshot of the current energy landscape and discusses several research and development opportunities and pathways that could lead to a prosperous, sustainable and secure energy future for the world.
In this study, a structural optimization method driven by tribo-dynamic mechanism is proposed for the staved water-lubricated bearings (SWLBs). To this end, a tribo-dynamic model considering mass conservation cavitation is established, and the accuracy of this model is verified by comparing it with the experimental and numerical results in published literature studies. The comparative studies emphasize the significant role of mass conservation cavitation on the tribo-dynamic responses of SWLBs under the mixed lubrication regime. Based on numerical simulations, the optimal stave structure for a specific working operation under heavy load condition is identified from the perspective of the tribo-dynamic mechanism. Furthermore, in order to evaluate the applicability of the proposed optimization method, the influences of key parameters, including the rotational speed, the radial clearance, and the surface roughness, on the optimization results are comparatively analyzed. The comparative results reveal that the optimal stave structure is highly dependent on the mentioned key parameters, and the optimal method is effective for a wide range of working conditions. Moreover, the effects of the stave parameters, including stave width and number, on tribo-dynamic characteristics of SWLBs are also investigated, suggesting a more comprehensive optimization scheme for SWLBs.
The connecting rod small-end bearing system is one of engine's rotating friction pairs under the most severe condition. Significant deformation, high temperature, and the coupling action of multi-bearing tribology and multi-body dynamics make the simulation challenging. This study develops a new tribo-dynamics model considering deformation and thermal effects for the small-end bearing system. A full-scale engine test is conducted, and the predicted severe wear position is consistent with the experimental one. Results show the axial uneven wear and temperature rise happens in the bearing lower surface after considering elastic deformation and thermal effects. The piston pin is decelerated to stop nearly and then accelerated by the friction torque during compression and work strokes that differs from the simplified rigid model.
As key friction pairs affecting the whole engine reliability, the piston-ring-liner system generates more than 45% of the whole engine friction loss. But so far, three-dimensional tribo-dynamic models considering its complex motions are very limited. This paper proposes a new method from the perspective of multi-flexible-body dynamics to realize a fully coupled modeling of the system’s deformation, dynamics, and lubrication characteristics. The study considers the ring-groove contact characteristics and calculates the system boundary loads through the blow-by model. The effect mechanism of ring groove deformation on ring properties is revealed, and the system’s complex tribo-dynamic behaviors such as twisting and fluttering are characterized. After fully coupled modeling, piston deformation at the ring groove position can be 65.80μm, resulting in a 1.33μm reduction in the minimum oil film thickness compared to the uncoupled model, and ring wear unevenness is aggravated.
With the increase on the power density of diesel engine, the looseness of connecting rod small end bushing becomes one of the main faults. In order to solve this engineering problem, the swing friction test bench was utilized to investigate the bushing friction temperature increase under different working conditions. The results show that the highest temperature of the bushing can be close to 300°C. To further analyze the influence of temperature increase on bushing looseness, bushing looseness tests were carried out at 25°C, 25→100→25°C(Heat from 25°C to 100°C, hold for 1 hour, and then cool to 25°C), 25→200→25°C, and 25→300→25°C. The test results show that the bushing looseness was greatly affected by the temperature increase, especially when the temperature was 25→300→25°C. The maximum pressing force of QSn7-0.2 bushing was reduced by 83.9% at 25→300→25°C compared with 25°C. The anti-loosening ability of the bushing can be improved by replacing the CuNi6Sn6 bushing material with higher strength ones as the maximum pressing force of the bushing was higher even though the temperature increased to 300°C.
Low-speed marine diesel engines are widely used as propulsion power equipment on ocean-going merchant ships. There are three important sliding friction pairs in the engine: piston assembly-cylinder liner, piston rod-stuffing box, and crosshead slipper-guide. They greatly influence the mechanical efficiency and stability of the engine. However, there is no effective method to measure the friction of the three friction pairs so far, which limits the improvement of tribological performance and the reduction of fuel consumption in low-speed marine diesel engines. In the current study, an indirect measurement method is presented and the measurement of the friction force under fired conditions is realized for the first time. By comparing the experimental results of friction force with the model-based numerical results, it is found that they are in good agreement. The difference between the numerical and experimental maximum friction force is less than 5%. Both theory and experiments show that the friction force reaches the maximum after the top dead center, which is about one-tenth of the gas force. The work of this paper is expected to provide an effective tool for evaluating the tribological performance of marine diesel engines.
Current mobility is highly dependent on fossil fuels which are the energy vectors of internal combustion engines, which power more than 99% of all road vehicles. In order to reduce pollutant emissions from ever growing urban centers, electric vehicles have emerged and their importance is growing steeply. However, these still face several problems regarding energy supply, storage and production, as well as life-cycle CO2 emissions. Nevertheless, there is a large fleet of vehicles with a vast majority of combustion-based power plants that need to be improved for a proper transition to total electrification. Therefore, it is essential that the remaining internal combustion engines become more efficient and sustainable energy conversion devices. For policy and business decision makers, understanding the trends of evolution is essential to making appropriate decisions. Thus, this study aimed at mapping the technological evolution of internal combustion engine and at understanding the main trends through patent data. The current stage of technological maturity was determined through a Logistics model, and the subtechnologies with the greatest potential for development and diffusion were analyzed. The search for the data was performed through Questel Orbit platform, in the United States Patent Trademark Office database. In 2018, internal combustion engine had a technological maturity rate of 81.77%. The subtechnologies that have the highest diffusion speed, among those compared, are: friction loss (32.14), water injection (21.05) and hybrid technology (20.88). It is forecast that internal combustion engines have approximately 27 years of estimated remaining time for saturation in the number of patent families.
Piston Skirt-Liner (PSL) system and Piston Pin Bearing (PPB), two key friction pairs in piston-assembly, interact with each other via impact and friction when transmitting the combustion load to crank train. Literature reporting such an interaction behavior in terms of tribology and dynamics is still rare, due to the complexity in a systematic modeling way. This paper proposed an efficient numerical model that fully couples these two friction pairs to investigate tribo-dynamic interactions between them. The model is built by coupling Reynolds-based mixed lubrication models for the friction pairs with Lagrange multibody motion equations for the piston-connecting rod-crank mechanism. Coupling effects between the piston skirt-liner system and the pin assembly are explored by comparing the cases contain the two friction pairs and one of them. Based on the above analyses, some design parameters including pin assembly clearance and pin offset, are further studied to disclose their influences on the tribo-dynamic performance of these two friction pairs. This work has a guiding significance for the systematic design of piston-assembly aiming to improve the dynamic property, economical efficiency and environmental-friendliness of engines.
The hermetic rotary compressor’s bearings, including the thrust bearing, the main and sub bearings, work together under high ambient pressure. The thrust bearing works under light axial loads, but sever wear is found, which may be related to the crankshaft’s misalignment and deformation and the high ambient pressure. To investigate this phenomenon, a complete coupled journal-thrust bearing model is constructed. The bearing forces are calculated with the mixed elastohydrodynamic model under high boundary pressure. The effects of the deformations and ambient pressure on the bearing performance are investigated. Results show that ignoring the crankshaft deformation makes the simulation underestimate the thrust bearing wear, and the high ambient pressure is the leading cause of the thrust bearing wear.
Lubricated full-floating pin bearings are being more and more widely used in the industrial products because of the advantages in terms of lubrication, scuffing resistance and durability. The present study develops a numerical model for the lubricated full-floating pin bearings in multibody mechanical systems by embedding the hydrodynamic lubrication and solid contact forces in the revolute joint clearance. The modified Coulomb law is employed to deal with the numerical difficulties caused by the pin stick-slip motion, while the MEBDF approach is applied to a high computation efficiency. An application example in a gasoline engine is then used to demonstrate the validity of the proposed model and reveal the friction reducing and anti-wear mechanisms for such pin bearings.
Robust and accurate measurement techniques are essential to studying the piston-assembly friction of Internal Combustion (IC) engines. Based on the instantaneous Indicated Mean Effective Pressure (IMEP) method, this paper develops an improved measurement technique to evaluate the piston-assembly friction in engines. Wireless teleme-try technology is employed in the measurement of connecting rod axial force, which greatly minimizes the engine modifications and enhances the measurement stability compared to the conventional wired way. The measurement system, which is composed of computer, data acquisition system, sampling trigger apparatus and sensors, is exploited with special attention given to the sampling synchronization of signal channels including cylinder pressure, connecting rod force and crank angle position. Engineering implementations are carried out on a four-stroke gasoline engine under motored condition. The measurement results are compared with numerical results from a newly developed numerical coupling model system, and it shows that the two agree well. In addition, the piston-assembly friction under different engine speeds and inlet lubricant temperatures are also measured, and analyses indicate that these results are in good correlation with the well-known Stribeck curve. This improved measurement technique provides an accurate and reliable option for the friction evaluation of piston-assembly components in engine designs.
Tilting pad journal bearing (TPJBs) have been widely used in rotating machinery such as compressors and turbines due to their superior stability compared to that of conventional fixed geometry bearings. As the adoption of TPJBs increases, various failure mechanisms related to TPJBs have been reported and pad wear is a frequently reported one. Pad wear causes geometry changes of the bearing, which can sometimes result in entire system failure. Therefore, it is important to detect the problem in the early stage to prevent unexpected system shut down. The objective of the current research is to investigate the influence of pad wear on the pad temperature, which is one of the widely used condition monitoring methods of TPJBs. For the theoretical investigation, thermohydrodynamic (THD) analysis was conducted by solving the generalized Reynolds equation and 3D energy equation. The developed THD model was validated by comparing the results with test data available in the literature. The results of the analysis showed that the temperature of the loaded pad increases and that of the unloaded pad decreases when wear occurred on loaded pads. In addition, the minimum film thickness also decreases with the wear depth. The validation test conducted with a test rig which mimics axial turbine where a test rotor was supported by two TPJBs. The test bearing consists of five pads with diameter of 60 mm and a resistance temperature detector (RTD) was installed in the pad for temperature monitoring. The test was performed by replacing the two loaded pads with the worn pad. The test result for TPJB with wear depth of 30 μm showed that the temperatures of the loaded pads were 8°C higher and that of the unloaded pad was 2.5°C lower than that of the normal TPJB. Additionally, the predicted pad temperature shows good agreement with the measured pad temperatures.
Wear is a typical failure form for mechanical parts of a reciprocating compressor. The clearance of a connecting rod bearing will exceed the normal value due to the wear caused by poor lubrication or abnormal loads. Wear on the small-end bush of a connecting rod (SEBCR) in a reciprocating compressor is still a hard work to be monitored and diagnosed. In this paper, we focus on the study of the dynamic response and diagnosis method on wear fault of SEBCR based on the dynamic simulation and vibration signal analysis. A rigid-flexible coupling model of a connecting rod has been built, and the connecting rod is treated as a flexible body. The clearance between the crosshead pin and the small-end bush of a connecting rod is taken into account. The simulation results show that abnormal clearance will affect the dynamic characteristic significantly, and high acceleration impacts will occur at the reversal points of the crosshead pin. Based on the dynamic response and signal feature extraction, a new diagnosis method calculating the amplitude and change rate of average vibration energy per crank angle to detect the wear fault is proposed. The experiment results on a reciprocating compressor show that the vibration of the compressor crosshead is consistent with numerical simulation results, and the method is capable of detecting the wear fault in real time. Research presented in this paper is significant in providing tools for diagnosing wear fault of reciprocating compressors.
In this paper, a semi-deterministic analytic thermal solution is presented for the rough textured ring/liner conjunction. The energy equation is employed to reveal more detailed information about the tribological performance of the textured surfaces in terms of the thermal effects and the viscosity change. The effects of surface texturing under the cold and warm engine conditions are studied over a wide range of engine speeds. It is shown that the thermal effects play a crucial role in hydrodynamic lubrication, particularly under the cold start condition. Including the thermal effects in the numerical simulation can ensure the accurate predictions.
For the past ten years, the loads applied on small end of conrods have become increasingly severe in automotive engines. Today, the necessity of numerical simulations of lubrication of these bearings has become an imperative concern for design engineers. However, the physical phenomenon related to the oil feeding of the small end bushes are generally not taken into account in industrial models. Moreover, the specific behavior of the small end bushes is rarely considered and could be sometimes misunderstood. To provide contributions to this problem, the analysis of the main parameters related to the lubrication of this kind of bearings have been carried out. Several characteristics of the oil feeding process have been investigated such as the influence of the clearance, the oil viscosity, the engine speed and specific configurations like grooves and oil holes. The study of their influences on the oil film thickness in the small end bushes have been realized. From these different investigations, some orientations have been drawn out in order to show what could be recommended for engineers to optimize this element.
In new engines, running conditions for piston pin bushes have become very severe due to combustion pressure and temperature increase. Moreover, the lead removal from the bush material has strongly reduced the capability of the antifriction material to accept asperity contacts, geometrical defects or edge loading. Today, it is usual that wear and seizure occur in the piston pin bushes during the first steps of engine development. In order to propose basic design recommendations avoiding damage, during the early steps of engine development, it is necessary to have quick numerical simulations. In these calculations, the mixed lubrication in the piston pin bearings must be taken into account. To obtain a simple realistic tool, a refined contact model is implemented in a simple hydrodynamic lubrication program. Then, the general behaviour of the piston pin is described before focusing on the combustion cycle phases when damage may occur. The oil film thickness variations during cycle are described and show what the critical phases are. Several parameters like pin diameter, temperature, pressure-viscosity coefficient have been investigated in order to understand their influence. To have an efficient wear modelling a special emphasis is put on the description of asperity contacts in order to built a wear model for bearings located on the piston pin. In this wear model, the surface topography parameters are taken into account in order to have a realistic approach and to identify the optimal roughness parameters.
Abstract This paper presents a state-of-the-art survey of papers reported on the nature of a troublesome failure mode in bearings known as seizure. This mode of failure is thermally-induced and it occurs in both journal and rolling element bearings. To gain insight, particular attention is given to reported experimental observation, various mechanisms involved, and available prediction methodologies.
Fuel economy of large, on-road diesel engines has become even more critical in recent years for engine manufactures, vehicle OEMs, and truck operators, in view of pending CO2 emission regulations. Demands for increased fuel economy are coupled with corresponding improvements in engine performance, durability, and emissions. This project centers on resolving the adverse effects on engine wear, durability, emissions, and oil consumption that often accompany traditional low-friction concepts. A detailed analysis of the sources of friction within a heavy-duty diesel engine was undertaken and empirical data on engine friction and component wear was collected from industry as well as from studies in literature. The use of thermal barrier coatings (TBC) was investigated as a novel approach to strategically increase cylinder liner temperatures in order to reduce power cylinder friction. By coating selected parts of the liner where piston speeds are high, local liner temperature is raised and local lubricant viscosity decreased in that region. In the mid-stroke, the piston is in the hydrodynamic lubrication regime, and high surface speeds generate the majority of the power cylinder work losses which can be reduced through reduced lubricant viscosity. By coating the liner in selected regions only, top dead center temperatures are mostly unaffected thereby minimizing any increase in cylinder liner wear. This approach is expected to maximize friction reduction while minimizing risk to other engine components or increasing component wear rates. A simulation was developed to model the primary physical processes that occur in a complete four stroke engine cycle. Calculations included work done by the piston, mass flow rates through the intake and exhaust valves, heat release during combustion, and heat transfer rates. The results demonstrate the potential to decrease power cylinder between 15% and 30% depending on coating thickness and application zone. This corresponds to approximately a 0.5% to 1% improvement in vehicle fuel economy. Additional fuel economy benefits from the TBC are expected from increased exhaust gas enthalpy and reduced liner heat rejection. This strategic thermal management approach within the engine has very high potential to increase engine efficiency while maintaining the performance and durability demanded in the HD engine market.
The finite-element technique discussed in this paper may be conveniently applied to study the effect of elastic distortion on journal bearing performance. The calculation procedure reduces to a set of nonlinear algebraic equations whose solution gives the elastohydrodynamic pressure distribution in the lubricant. Since the method is not restricted to a particular bearing geometry, it can be applied to any realistic bearing configuration. It was also found that the direct iterative technique, namely, film thickness-pressure-film thickness-pressure, etc. , converges only when the elastic distortion is small compared to the clearance space. The iterative scheme used in this work was found to be effective at eccentricity ratios as high as 1. 15 when the displacements are of the same order of magnitude as the initial clearance. The sample problem shows that the elastohydrodynamic pressure distribution is significantly different from that obtained by neglecting elastic distortion.
A new approach is utilized to determine the effects of surface roughness on partially lubricated contacts. An average Reynolds equation for rough surfaces is defined in terms of pressure and shear flow factors, which are obtained by numerical flow simulation. Through the use of measured or numerically generated rough surfaces, any three dimensional roughness structure can be analyzed with this method. The average Reynolds equation is obtained for isotropic surfaces, and for surfaces with directional patterns. The flow factors for these surfaces are expressed as empirical relations in terms of h/σ and a surface characteristic γ defined as the ratio of x and y correlation lengths.
The Average Flow Model introduced in an earlier paper is extended to include sliding contacts by deriving the shear flow factor for various roughness configurations. Similar to the pressure flow factors, the shear flow factor is obtained through numerical flow simulation on a model bearing having numerically generated roughness. The flow factors for isotropic and directional surfaces are expressed as empirical relationships in terms of h/ sigma , a surface pattern parameter gamma defined as the ratio of x and y correlation lengths, and the variance ratio V//r//1 which is the ratio of variance of surface 1 to that of the composite roughness. Expressions for the mean shear stress and horizontal force components due to local pressure in rough bearings are derived through the definition of shear stress factors, also obtained through simulation. The application of the average Reynolds equation to analyze roughness effects in bearings is demonstrated on a finite slider. The effects of the operating parameters as well as the roughness parameters on mean hydrodynamic load, mean viscous friction and mean bearing inflow are illustrated. A discussion of the paper is appended.
A general method is derived for the solution of the Reynolds equation including the effects of tangential and normal velocities. It is applied to the solution of a full journal bearing under a fluctuating load with no journal rotation. The characteristics of a finite journal bearing under a cyclic sinusoidal load are shown in curve form.
A piston pin joint in a modern diesel engine operates under extreme loading and lubrication conditions. High load in combination with low relative surface velocities and limited lubrication makes this joint prone to localized wear and sudden failure. The analysis of this joint is also complicated with the pin motion, which defines surface velocities in the pin bore to pin and the pin to connecting rod interfaces. Therefore, the entire joint needs to be analyzed as a system of two bearings. Also, the hydrodynamic pressure in this joint at times may not be sufficient to balance the force applied to the joint and has to be complemented by the asperity contact pressure. The latter causes an additional deformation of the bearing. To address this problem a mixed lubrication model has been developed based on spectral EHD and nonlinear Greenwood and Trip statistical asperity contact formulation. Contact pressure distributions calculated with this model showed a pattern similar to the wear pattern in the bushing after production test. Analysis of the heat generated in the bearing was found to be a good indicator for the severity of the regime. Analysis of the bushing and piston bore with different geometry showed that asperity contact pressure and heat generated in the joint can be significantly reduced by modifications in local shape of the contacting surfaces.
From the Publisher:
Intended for introductory courses in numerical analysis,this book features a comprehensive treatment of major topics in this subject area. Using an algorithmic approach,it provides numerous worked examples with computer output,and flowcharts and programs.
The assumption of axisymmetry, employed by most of studies on piston ring lubrication, probably gives a too idealistic model for the real situation. A theoretical model for a nonaxisymmetrical analysis of piston ring lubrication has been established in the present study. When a piston ring with an arbitrary free shape is fitted into the cylinder bore, the determination of ring deflection and contact load has been modeled mathematically as a Linear Complementary Problem (LCP). By combining LCP solution with lubrication analysis, the film thickness and contact load distribution over the circumference are obtained, leading to a more realistic simulation for piston ring lubrication. The friction force between piston ring and cylinder bore is predicted by the mixed lubrication model including the effects of surface roughness and asperity contact. The static distortion of cylinder bore, gas pressure variation, and lubricant starvation are also considered in the simulation. Results show that the contact pattern and film thickness between piston ring and cylinder bore are not exactly axisymmetrical. The main reason for the nonuniform contact is the asymmetry of ring elasticity, the static distortion and dynamic load created by the secondary movement of piston skirt.
The engines in vehicles today are smaller in size and lighter in weight but are still required to produce high output power. These characteristics have been found to induce thermal problems in the engine. In solving this thermal problem, temperature measurement in the piston of the engine plays an important role. However, owing to the environment of the piston, it is difficult to measure the temperature in the piston. Thus, developing a method to measure the temperature of the piston is currently an important research topic. This paper presents a piston temperature telemetry system that was developed using Bluetooth. This system is advantageous in that it makes it possible to measure multipiston temperature using a Bluetooth wireless network, which is an area that has yet to be investigated in more depth. The telemetry system is composed of the piston part and the data acquisition part. To evaluate the performance of the telemetry system, experiments were conducted using a 2359 cm(3) DOHC engine produced by the Hyundai Motor Company. The experimental results show that the piston telemetry system is applicable to real commercial engines for measuring piston temperature.
Piston assembly friction measurement has been carried out on a single cylinder gasoline engine using the IMEP (indicated mean effective pressure) method at realistic engine speeds and loads without any major engine modifications. Instantaneous and mean piston assembly friction were measured under motored and fired conditions at different lubricant temperatures. The forces acting on the piston assembly were carefully determinated by measuring the cylinder pressure, crankshaft angular velocity and strain in the connecting rod. The difference between the resulting gas pressure, inertia and connecting rod axial forces acting on the piston yields the piston assembly friction. To achieve this with confidence, an advanced instrumentation, telemetry and data acquisition system was designed and developed, giving special attention to the synchronisation and simultaneous sampling of analogue and digital channels. Experiments are reported for piston assembly friction at a range of engine operating conditions with different lubricant formulations, with and without a friction modifier.
The effect of roughness on lubrication is considered. The research outlined in this paper was motivated by the need to find directly simple relationships between ∂h/∂x and ∂h̄T/ ∂x, ∂h/∂t and ∂h̄T/∂t instead of h and h̄T, where h = nominal film thickness (compliance); h̄T = average gap (separation). A dimensionless parameter called the contact factor is derived from the roughness deformation and probability theory. The introduction of the contact factor makes the average Reynolds equation not only much simplified but also more suitable for studying partial hydrodynamic lubrication and elastohydrodynamic lubrication. The contact factor is the probability that the surfaces are really lubricated, and this makes the physical meaning of the average Reynolds equation clearer.
Experimental results of steady dimples measured in elliptical glass-steel contact under pure sliding conditions are presented. It is found that two dimples connected with a shallower furrow are generated, each near an end of the major radius of the contact ellipse. The complete solution of the corresponding thermal elastohydrodynamic lubrication (TEHL) problem is calculated numerically. Good agreement is obtained between the experimental and theoretical results. This agreement can be explained by the temperature-viscosity wedge mechanism. Correctness of this mechanism is demonstrated using additional experiments with ceramic balls in contact with glass and sapphire disks.
Surfaces and subsurfaces of test specimens that failed in scuffing were examined. A scuffing criterion is developed stating that scuffing failure would occur when the maximum surface tangential traction is larger than the modified shear strength. A scuffing uncertainty factor is introduced to reflect the influence of factors that affect wear and scuffing and the inaccuracy in modeling.
Performance analysis of a piston ring pack is presented in this investigation with the objective of studying the behavior and interrelationships of key engine parameters such as oil consumption, blow-by/blow-back, power loss and wear loads for typical operating conditions. The analysis is based on an integrated methodology addressing the various physical phenomena associated with ring packs including (a) ring dynamics for axial and twist motions within the grooves to determine flow paths for gases, (b) inter-ring gas dynamics for blow-by and blow-back behavior, (c) mixed lubrication at the ring face-liner conjunction for friction considerations and radial ring dynamics, and (d) oil transport for distribution of lubricant along the liner. Relevant output from each of these phenomenological models such as instantaneous values of (i) inter-ring flow areas, (ii) gas blow-back, (Hi) volume of oil within inter-ring regions, (iv) oil accumulation at top ring's leading edge and (v) liner oil film distribution are utilized by the oil consumption models which enable the calculations from the various consumption mechanisms (due to throw-off, entrainment and evaporation). Additionally, wear loads on the ring faces and liner are calculated based on contact pressures due to mixed lubrication at the ring face-liner interface. Included in this investigation are results from a series of studies undertaken to analyze the behavior of the aforementioned engine parameters over a range of speed and load conditions.
The interpretation of certain phenomena occuring at nominally flat surfaces in stationary or sliding contact is dependent on the assumed distribution of the real area of contact between the surfaces. Since there is little direct evidence on which to base an estimate of this distribution, the approach used is to set up a simple model and compare the deduced theory (e.g., the deduced dependence of the experimental observables on the load) with the experimental evidence. The main conclusions are as follows. (a) The electrical contact resistance depends on the model used to represent the surfaces; the most realistic model is one in which increasing the load increases both the number and size of the contact areas. (b) In general, mechanical wear should also depend on the model. However, in wear experiments showing the simplest behavior, the wear rate is proportional to the load, and these results can be explained by assuming removal of lumps at contact areas formed by plastic deformation; moreover, this particular deduction is independent of the assumed model. This suggests that a basic assumption of previous theories, that increasing the load increases the number of contacts without affecting their average size, is redundant.