The effect of a friction modifier on piston ring and cylinder bore friction and wear

The addition of friction modifiers to crankcase lubricants has been shown to significantly reduce the mechanical losses of critical components in internal combustion (ic) engine; thereby improving fuel economy.In this study the friction and wear of a piston ring/cylinder bore material combination was studied using a pin-on-plate laboratory tribo-test machine developed to reproduce the wear mechanisms encountered in an ic engine. Two lubricants were evaluated: (i) a standard SAE 30 grade diesel formulation, and (ii) the same formulation with the addition of a 5% soluble MoS₂ friction modifier.Analysis of the wear results identified three periods of wear: (1) running-in, (2) transient wear and (3) terminal wear. Throughout this study particular emphasis has been placed on the simulation of the wear mechanisms occurring within engines. Surface analysis confirmed that both abrasive wear and delamination wear was produced.Friction benefits attributable to the addition of MoS₂ friction modifier were obtained. However, under specific conditions the wear rate increased due to increased abrasion of the plate.     

Engine friction lubricant sensitivities: A comparison of modern diesel and gasoline engines

Engine friction models have been developed that take account of the variations in lubricants with temperature, shear rate, and pressure. These models have been used to study the lubricant sensitivities of modern diesel and gasoline engines. Total engine friction losses for a Perkins Phaser four‐cylinder, 4.0 l, turbocharged, inter‐cooled diesel engine, operating at 1300 rpm, with an SAE 15W‐40 lubricant, were estimated at approximately 2 kW, with the piston assembly contributing 46%, the bearings 49%, and the valve train 5%. Total engine friction losses for a Mercedes Benz M111 2.0 l gasoline engine (used in CEC sludge and fuel economy engine tests) operating at 2500 rpm, and medium load, for an SAE 15W‐40 lubricant, were estimated at 1.5 kW, with the piston assembly contributing 42%, the bearings 39%, and the valve train 19%.     

A tribological investigation of lubricant effects on bearing friction and fuel economy for passenger car engines and heavy duty diesel engines

Rising fuel costs and the need to conserve fossil fuel have led to increased interest in the role of lubricants in improving fuel economy. Crankshaft bearings can account for up to 40% of engine friction. Lubricant formulations can provide a beneficial reduction in engine friction, thus improving fuel economy. A unique journal bearing test rig has been developed to evaluate lubricants under transient and steady‐state conditions for passenger car engines and heavy duty diesel engines. The rig can measure bearing friction over a wide temperature, speed and load range. The rig uses production components and can be operated so as to produce the bearing pressures, lambda ratio and shear rates experienced by lubricants in fired engines. The properties of a range of lubricants of varying viscometrics, including Newtonian, non‐Newtonian and fully formulated oils have been evaluated. Significant differences due to formulation have been observed. The results of the study have been compared to fuel economy data generated from fired engines with the same lubricants as those tested in the journal bearing rig. Copyright © 2006 John Wiley & Sons, Ltd.     

A new test technique for the laboratory evaluation of energy-efficient engine oils

Testing lubricants for fuel economy is a significant part of the drive for energy conservation. Generally, the small differences in fuel economy between lubricants make measurements inherently uncertain. Furthermore, precise engine tests for assessment of energy efficiency are expensive and time consuming. There has been a need, therefore, for the development of an effective laboratory screening technique to assess the energy efficiency of engine oils. With this objective in view, a new test technique consisting of two different tests has been developed for measuring lubricant-related fuel economy. Fuel economy through the use of engine oil is achieved by reducing boundary friction and viscous friction. Whereas reduction in boundary friction is obtained through the use of friction modifiers in engine oil, viscous friction is reduced through the use of low viscosity oils and by multigrading. The efficacy of action of friction modifiers in reducing boundary friction has been assessed with a SRV-Oscillating Friction and Wear Tester, using point and piston ring/liner segment contact. For the measurement of viscous friction, an attempt has been made to find out the reduction in viscous friction by using low viscosity oils and multigrade oils on a SAE No. 2 Machine, with all-steel clutch plates.     

Numerical evaluation of the potential for fuel economy improvement due to boundary friction reduction within heavy-duty diesel engines

Advanced surface treatments have been developed by a number of research institutes as an approach to reduce friction at sliding interfaces. Laboratory tests have shown that some of these surface treatments can result in boundary friction reductions approaching an order of magnitude [1], [2] and [3]. While there are many potential applications for such surface treatments, friction reduction in internal combustion engines is of particular interest due to the apparent fuel savings potential. Ricardo, Inc. has performed simulations to estimate potential fuel economy improvements due to the application of such treatments at key interfaces within engines typical of those used in large trucks. The results show that fuel economy improvements in excess of 4% can be achieved from combined application of a surface treatment and reduction in lubricant viscosity, if the surfaces can be protected against wear.     

Reliable model of lubricant-related friction in internal combustion engines

A linear model of lubricant-related engine friction was developed. Based on lubrication fundamentals, the technique is comprised of three simple bench tests that respectively operate under thick fluid-film hydrodynamic lubrication, elastohydrodynamic lubrication, and boundary lubrication. With adequate configuration and appropriate test conditions, these bench tests are seen to simulate major friction losses in a typical internal combustion engine. Lubricant characteristics obtained in the bench tests were combined using SAS linear regression and correlated to ASTM Five-Car and Sequence VI engine tests. The linear model gave an excellent prediction of engine data. It further showed that hydrodynamic friction losses dominate lubricant-related engine friction, followed by boundary friction losses, and elastohydrodynamic or mixed friction losses. This simple, reliable, and inexpensive technique can be used as a research tool to study friction characteristics of crankcase lubricants and to develop superior fuel-efficient engine oils. Major findings from this study can be summarised as follows:

• 1 The linear model predicts that 5 to 6% fuel economy improvement over the industry high reference oil HR-4 is achievable with today's motor oil technology
• 2 Hydrodynamic friction losses in both ‘thick' and ’thin' fluid-film lubrication account for 63% of total friction losses caused by the engine oil while boundary friction losses amount to 37%.
• 3 Friction losses in the elastohydrodynamic (EHD) engine are significant, up to 22% of total friction losses. This, combined with the fact that EHD film thickness is the most significant parameter in the linear model, suggests that pressure effects (ie, high-temperature/high-shear/high-pressure viscosity, pressure-viscosity coefficients) are important.
• 4 Increasing fuel economy improvement is in general in the order: SAE 10W–40 < SAE 10W–30 < SAE 5W–30, providing that base stock and additive systems are unchanged.

     

The shell low velocity friction machine for evaluating fuel economy motor oils

Reduction in friction between rubbing surfaces (i.e. boundary friction) in engines gives better engine efficiency and hence fuel economy; this can be obtained by adding suitable boundary lubricating additives to the motor oil.A simple method of measuring the boundary friction of motor oils was devised using a modified Shell four-ball machine. The results obtained showed broad agreement with fuel economy findings obtained with a car on a test track.     

Demonstrating Improved Fuel Economy Using Subsystem Specific Lubricants on a Modified Diesel Engine

Fuel economy performance in modern internal combustion engines is of increasing importance to lubricant formulators due to regulations targeting global greenhouse gas emissions. Engines typically employ a single lubricant, with a common sump, to service all components. As a result, base oil and additive selection for fuel economy performance is a compromise among competing demands for different engine subsystems. Opportunities for significant fuel economy improvement through targeted formulation of lubricants for specific engine subsystems are presented, with specific emphasis on segregating the lubricant supplies for the valve train and the power cylinder subsystems. A working prototype was developed in a lab environment by modifying a commercially available twin-cylinder diesel engine. Motored valve train and whole-engine fired test results were obtained and compared to model data. Fuel economy benefits were demonstrated using market representative heavy-duty diesel lubricants, including mineral oil and polyalphaolefin (PAO) blends. The fuel economy benefits of a dual-loop lubricant system are demonstrated through significant viscosity reduction in the power cylinder subsystem, achieving overall engine friction reductions of up to 8% for the investigated operating condition. Results suggest that additional gains may be realized through targeted base oil and additive formulation. Implications for incorporation in larger diesel engines are also considered.     

Chemical and Physical Analysis of Reaction Films Formed by Molybdenum Dialkyl-Dithiocarbamate Friction Modifier Additive Using Raman and Atomic Force Microscopy

In order to improve the fuel economy of engines it is now common to include in modern engine oils small quantities of soluble, molybdenum-based friction-reducing additives. These additives are generally believed to form MoS₂ in rubbed contacts and thereby reduce friction in boundary lubrication conditions. This paper describes the application of Raman and atomic force microscopy to study the reaction films formed in rubbing contacts by simple solutions of molybdenum dialkyl-dithiocarbamate additive. Raman microanalysis shows that MoS₂ is present in the wear scars produced whenever this molybdenum additive effectively reduces friction. In reciprocating friction tests, the MoS₂ is unevenly distributed in the wear scar, with more in the centre of the stroke than at the reversal points. This explains the experimentally observed influence of stroke length on friction. Atomic and lateral force microscopy show that when the additive effectively reduces friction, tiny, discrete, flake-like low friction domains are present in the wear scar. These are typically 10–25 nm in diameter and 1–2 nm thick and are believed to represent MoS₂ nanocrystals as have been previously reported in the literature using high-resolution TEM. Coupled topography and lateral force measurements shows that these nanocrystals are present only on the high spots of the rubbed surface.     

Friction modifiers in engine and gear oils

Reducing friction is an important target for any lubricant oil formulator. There are several ways, such as utilisation of multi‐grade oils with low viscosity at low temperature, or use of friction modifiers, to reduce friction in automotive engines and transmissions and thus save fuel. A good means to obtain an energy‐saving lubricant is by the addition of a friction‐reducing additive in a high‐range multigrade oil. This paper presents some considerations on the action mechanism of friction modifiers and the results obtained in engine and gear oils with two new nitrogen‐, sulphur‐, and boron‐containing additives.     

Global energy consumption due to friction in trucks and buses

In this paper, we report the global fuel energy consumption in heavy-duty road vehicles due to friction in engines, transmissions, tires, auxiliary equipment, and brakes. Four categories of vehicle, representing an average of the global fleet of heavy vehicles, were studied: single-unit trucks, truck and trailer combinations, city buses, and coaches. Friction losses in tribocontacts were estimated by drawing upon the literature on prevailing contact mechanics and lubrication mechanisms. Coefficients of friction in the tribocontacts were estimated based on available information in the literature for four cases: (1) the average vehicle in use today, (2) a vehicle with today׳s best commercial tribological technology, (3) a vehicle with today׳s most advanced technology based upon recent research and development, and (4) a vehicle with the best futuristic technology forecasted in the next 12 years. The following conclusions were reached:

• •In heavy duty vehicles, 33% of the fuel energy is used to overcome friction in the engine, transmission, tires, auxiliary equipment, and brakes. The parasitic frictional losses, with braking friction excluded, are 26% of the fuel energy. In total, 34% of the fuel energy is used to move the vehicle.
• •Worldwide, 180,000 million liters of fuel was used in 2012 to overcome friction in heavy duty vehicles. This equals 6.5 million TJ/a; hence, reduction in frictional losses can provide significant benefits in fuel economy. A reduction in friction results in a 2.5 times improvement in fuel economy, as exhaust and cooling losses are reduced as well.
• •Globally a single-unit truck uses on average 1500 l of diesel fuel per year to overcome friction losses; a truck and trailer combination, 12,500 l; a city bus, 12,700 l; and a coach, 7100 l.
• •By taking advantage of new technology for friction reduction in heavy duty vehicles, friction losses could be reduced by 14% in the short term (4 to 8 years) and by 37% in the long term (8 to 12 years). In the short term, this would annually equal worldwide savings of 105,000 million euros, 75,000 million liters of diesel fuel, and a CO₂ emission reduction of 200 million tones. In the long term, the annual benefit would be 280,000 million euros, 200,000 million liters of fuel, and a CO₂ emission reduction of 530 million tonnes.
• •Hybridization and electrification are expected to penetrate only certain niches of the heavy-duty vehicle sector. In the case of city buses and delivery trucks, hybridization can cut fuel consumption by 25% to 30%, but there is little to gain in the case of coaches and long-haul trucks. Downsizing the internal combustion engine and using recuperative braking energy can also reduce friction losses.
• •Electrification is best suited for city buses and delivery trucks. The energy used to overcome friction in electric vehicles is estimated to be less than half of that of conventional diesel vehicles.

Potential new remedies to reduce friction in heavy duty vehicles include the use of advanced low-friction coatings and surface texturing technology on sliding, rolling, and reciprocating engine and transmission components, new low-viscosity and low-shear lubricants and additives, and new tire designs that reduce rolling friction.     

A Study of Piston Friction Force in an Internal Combustion Engine

Quantitative estimation of friction losses in the initial design stage of an automobile engine is a crucial issue that determines the fuel economy and performance of the automobile. However, measurements and mathematical treatments of friction losses were difficult, and practical estimation methods were scarce.

This study was carried out due to such circumstances, with emphasis placed on the analysis of mechanism of friction losses of the piston system, and the introduction of practical equations for calculation of those friction losses.     

Contemporary challenges of soot build-up in IC engine and their tribological implications

Confronted with the contemporary challenges of maximising energy efficiency with minimal impact on the environment, the automotive industry has developed various technologies to tackle them. Most of these technologies, however, have wider implications on the tribological performance of the automotive engines due to resultant soot build-up. This paper reviews the effects that attempts by stakeholders to satisfy requirements for reduced fuel consumption, reduced emissions and extended service intervals have had on increasing soot levels to an extent that can lead to engine component failure. Three areas have been identified that have either not been explored or not widely explored in the study of automotive soot namely: numerical simulation and modelling of soot wear, soot effects on wear of actual engine components and the wear and friction performance of non-metallic materials used in internal combustion engines. A paper-grading system is also utilised to present an overview of how sooty oil-related research covers various areas.     

Antifriction action of lubricant additives

The influence of antifriction additives for engine oils on fuel economy in gasoline engines has encouraged an interest in research into their action mechanisms. The influence of additives of different types on the antifriction properties of engine oils has now been investigated; additives have been discovered which effectively increase thermal stability of the lubricating layers and decrease friction coefficient, even at high temperatures. The structure and composition of the surface layers of friction pairs have been studied with Auger electron spectroscopy. The inter-relationship between the effectiveness of the antifriction action of the additives and their influence on the thickness and the composition of the surface layers has been ascertained. The most effective antifriction action was obtained where the thickness of the surface layers was reduced within certain limits, and where there was an optimisation of the oxygen and sulphur content. Certain regularities were established, since they were noticed while testing antioxidant, antiwear, antifriction, and detergent additives of different composition.     

Impact of the Oil Temperature on the Frictional Behavior of Laser-Structured Surfaces

This study investigates how the beneficial effects of laser-manufactured surface microstructures on friction vary with varying oil temperature. Laser surface texturing (LST) is a favorable method to optimize friction and wear, which have always been considerable obstacles against the performance improvement of combustion engines. The aim of this study is to detect correlations between the dimensional parameters of the laser-textured surfaces and tribological performance at varying temperatures. Although the experiments are on a fundamental level, the obvious application of combustion engines has been selected to align the material, processing, and test parameters. A wide range of micro indentations—henceforth called “dimples”—were fabricated onto honed flat aluminum samples by means of ultrashort pulse laser texturing and the frictional behavior at different lubricating oil temperatures (30 and 90?°C) was analyzed.     

Functional properties of microstructured cylinder liner surfaces for internal combustion engines

Internal combustion engines are still of major importance as propulsion systems. To fulfil future market and legislative demands it is necessary to improve engine performance, reduce fuel consumption, and limit exhaust emissions. Mechanical and thermodynamic losses, wear, and the emissions caused by lubricating oil combustion are principally influenced by the tribological behaviour of the piston assembly. The trend towards compact engines with high power densities and increased thermomechanical loads increases the importance of this tribological system and requires new approaches. One promising possibility is the utilisation of liner surfaces with specially machined microstructures. This paper describes a comparison between a conventional liner surface and a laser‐structured liner as regards their tribological behaviour. Measurements of wear as well as of oil film thickness and friction force in operation have been carried out. The results show better tribological behaviour for the laser‐structured liner surface than for the conventional plateau‐honed surface. This leads to lower fuel consumption and less wear.     

船用低速机关键摩擦副建模分析与摩擦力无线测量验证

低速机结构复杂,其关键摩擦副的性能对船舶运营的经济性、安全性和稳定性有重要影响,然而,目前对低速机摩擦学问题的理论和试验研究很少.对船用低速机关键摩擦副进行建模分析,并对摩擦力进行无线测量验证.结合多体动力学和混合润滑理论建立了低速机关键摩擦副的多学科耦合仿真模型,实现对各摩擦副性能的预测;进而,基于间接测量思想,提出...     

齿轮滑油对轿车齿轮传动效率和燃油经济性的影响

1．首先应当考虑轿车的油耗只和摩擦学有关,其中影响最明显的是润滑油。2．采用测量润滑方法只能阐述机械损失,因此,燃油经济性实现改善的可能性受到了限制,特别当考虑齿轮高效率的时候,3．在评价粘性对燃油消耗的影响时,所谓粘性必须考虑有效粘性,对这非牛顿油是非常重要的,4．按SAE粘度梯度降低齿轮油粘度,将可使燃油消耗在高温时降低0．2－1．5％,低温时降低0．4－2．5％。5．在齿轮油中应用摩擦改良时,燃油消耗的实际降低在1．0－6．0％之间。6．减少摩阻50％的基础上,考虑不同的传动过程,燃油消耗降低为其他齿轮油1．0－5．1％之间。7．汽车齿轮试验,使燃油消耗改善大小顺序按为其他齿轮油1％。8．测量结果确定计算估价的原则。     

Analysis of engine temperature and energy flow in diesel engine using engine thermal management

Recently, precise analysis of energy flow in engines has become necessary to improve fuel economy. An integrated engine thermal management model, which is introduced in this paper, is suitable for that process. The model consists of six sub-models for thermal mass, coolant, lubricant, heat transfer, friction, and exhaust. The sub-models are coupled to each other and they exchange heat and signals. Combustion energy flow analysis and temperature estimation of the engine components and working fluids were simulated under various conditions. Simulation results were compared with experimental data and they showed good agreement. Then, a variable-speed water pump (VSWP) to control coolant flow was applied in place of a conventional water pump. Engine warm-up time decreased with proper coolant flow control, and fuel economy could be improved by 2.5%.     

汽车的节能要求与润滑剂技术的发展

介绍了发动机油节能试验的发展和润滑剂流变性质、润滑油摩擦改进剂等对燃油经济性的影响和作用机理。指出了发动机油的流变性能是影响油品节能效果的重要因素,具有合理高温高剪切粘度的高粘度指数、低粘度和低粘压系数的发动机油利于节能;通过吸附作用而起到减摩效果的有机摩擦改进剂在中等温度条件下具有明显的减摩作用,利于改善发动机油的节能效果;深度精制的高粘度指数基础油的使用可以提高发动机油节能效果和保持能力。