|
|
|
|||||||||
|
|||||||||
|
|||||||||
By Tomasz W. Liskiewicz, Ardian Morina and Anne Neville
TRIZ provides a number of tools to not only solve, but also to properly define, problems. The definition stage is crucial for the successful output of the project and sometimes can be more time consuming than the solution stage. The problem definition techniques based on TRIZ have been applied to: 1) indicate if there is a room for development of current lubrication technology, 2) place the investigated problem in time and space and, finally, 3) prepare for the next stage of dealing with TRIZ – application of an appropriate problem solving tool.
From the authors' observations, engineers tend to find it difficult to devote much time to the problem definition stage. They may think they have defined the problem properly, but actually they have only partially done so. Working on the final solution can be more attractive than looking closer at the problem, even if intensive and in-depth problem analysis typically leads to more ideal solutions in a shorter period of time. Problem definition techniques force the engineer to look at the system from a perspective different from where the problem is set. As Albert Einstein once stated, "Problems cannot be solved by thinking within the framework in which the problems were created."
The problem definition stage is an integral part of TRIZ, with four stages shown in Figure 1. TRIZ provides systematic problem definition tools that encourage users to devote more time to identify and formulate the problem and facilitate the analysis of input data. In that sense, TRIZ ensures that the effort is directed toward solution of a real problem and no time is wasted on answering inappropriate questions. If the problem is not properly analyzed the loop of stages 1 to 4, the loops needs to be repeated – taking more time than a single generic process with a deep analysis of the problem. The problem definition stage identifies contradictions, benefits and harmful effects within a problem, which is crucial for the selection and solving stages in the TRIZ framework.
| |||||
The aim of this paper is to analyze lubricant additives technology for the internal combustion engine with systematic problem definition tools provided by TRIZ. This analysis will determine if the current technology can be further developed or if a completely novel solution is required to meet the challenges of future lubricants market.
The lubrication process is found within the field of science called tribology. The term tribology is related to the mechanisms of friction, lubrication and wear of interacting surfaces under relative motion.2 The current effort on lubricant performance in internal combustion engines is mainly focused around additive technology. The main studies are directed toward the understanding of mutual interactions between additives and the material surface.3,4,5 Commercial engine oils contain a number of additives with different functions: to control friction and wear (viscosity index improver, anti-wear additive, friction modifier, corrosion inhibitor), to reduce contamination, maintain cleanliness (anti-oxidant, dispersant, detergent) and to maintain fluid properties (pour point depressant, anti-foam additive).
The performance of the contact in terms of friction and wear is dependent on the formation of a tribofilm, which is supported by presence of the adequate additives. The tribofilm is a very thin layer (~150nm) that covers the surface irregularities and has the following beneficial properties:
If the proper oil composition is not used, metal-to-metal asperity contact occurs and high friction and wear rates take place.
Passenger and commercial light vehicles have been estimated to account for 20 percent of the total CO2 delivered into the atmosphere from hydrocarbon sources in the United States and other developed countries.6 When the population of vehicles in the Western world is considered, it is easier to see how a realistic link between tribology and ecology can be made. According to recent United Kingdom government statistics, in 2005 in the UK alone there were 32 million motor vehicles registered for use on the public highway.7 International numbers are even more impressive, with the total number of road vehicles in service in the U.S. in 2003 at 200 million.8 Bearing in mind that this excludes the rest of Europe, all of Asia, Australasia, Africa and South America, the staggering scale of the use of the reciprocating internal combustion engine becomes clear.
Incremental steps are being made to move toward environmentally-acceptable solutions to achieve target COx and NOx emissions, alongside retained engine performance but these are unlikely to deliver any more than an insignificant move to keep in line with the shifting targets imposed by government. The broader scope of this project, beyond analyzing the field of engine lubricants technology, is to find a radically new way of lubricating engines that is both effective and environmentally friendly.
In this study, the following three problem definition analyzes have been carried out to assess the current lubricant additives technology: 1) system operator – for thinking in time and space, 2) S-curves – to define how mature the current system is and 3) ideal final result (IFR) – to find out how the ideality can be increased.
This concept, called also 9-windows, is usually applied to overcome natural psychological inertia and to reflect where the solution of the problem might lie. By working on all eight windows surrounding the central "local quality," the problem is approached globally in time and space. The technology system is encapsulated in a three-by-three matrix with different time levels in the horizontal direction: past, present, future and different scale levels in the vertical direction: sub-system, system and super-system.
From the tribological performance point of view, the tribofilm should be a central point of the analysis in time and space as it provides key properties of the system: low friction and low wear. (See Figure 2) Formation of the tribofilm is in present within the time space as it is formed only under rubbing conditions. Tribofilm does not exists in the past, i.e., before friction takes place. The additives and base oil are on the sub-system level in relation to the main system object. The super-system is associated with the tribological interface, where two rubbing components are separated by the tribofilm.
| |||||
The characteristic manner of the S-curve describing the evolution of systems in time has been proven by researchers from different areas (engineering, biology, economy). TRIZ recommends that the S-curve is analyzed in order to determine the ideality of the current system and, as a result, to decide if there is potential for further development or whether a novel (and often radical) approach is required.
Solid line = ideality evolution of the first generation of the product; | |||||
Ideality is defined as benefits divided by the sum of cost and harm. Here, the benefits are related to low friction and low wear, cost factor to lubrication expense and harm factor to environmental issues, which can be quantified by fuel economy and pollutants.
The basic concept of decreasing friction by application of the fluid dates back to ancient Egypt, when olive oil was poured under the runners of great sledges dragged by the power of human muscles to reduce friction. Nevertheless, the birth of real lubrication coincides with the technical revolution at the beginning of the twentieth century. The sudden growth of the main classes of lubricant additives took place in the 1930s and 1940s when the need for well-lubricated and reliable machines increased rapidly, partly due to wartime demands. (See Figure 4) From the 1950s until now lubrication technology has been developed continuously.
Significant progress toward optimizing current additive technology has been made in parallel with evolution of chemical characterization tools. "Design" of additives was made possible once the key functionality of additives was delivered. Molecular modeling introduced in the last 10 years has added to the capabilities of synthetic chemists in being able to develop functional additives. There is little doubt that the speed at which lubricant additive technology is evolving has slowed in the last decade – partly due to the ever-increasingly stringent legislative constraints imposed on additive manufacturers. Taking into account that legislation will inevitably force further reduction of phosphorus and sulphur to extremely low levels, the ideality of a lubrication technology is likely to drop from the current level. The removal of those compounds will dramatically decrease the benefits unless effective replacements are found.
| |||||
There are four quantitative properties of the system proposed by Genrich Altshuller and his colleagues, which translates into the performance of the system in the S-curve: 1) profitability over time, 2) number of inventions or patents over time, 3) performance over time and 4) level of inventiveness over time.10 It has been also proposed to relate the ideality of the system to the number of competing companies on the market.11 This trend illustrates the situation in the lubricant industry in the U.K. There were around 600 lubricant manufacturers on the market just after World War II, around 250 in the 60s, some 80 in the 90s and now there are less than 50 lubricant suppliers.12
This radical tool requires thinking in terms of a desired solution, focusing on the ideal system. By approaching the problem without any constraints and trying to imagine the ideal solution, the situation "where we are" is compared with the situation "where we would like to be." The starting point is a solution that is completely perfect (e.g., no cost, no wear, self-healing). Problem solvers then work back from the IFR, applying minimum compromises at each stage, as shown in Figure 5.
S = sulphur, P = phosphorus | |||||
The ideal lubricated system would be environmentally friendly and would perform spontaneously under rubbing conditions. It is not necessary to produce the tribofilm (as it is in the current technology) as long as the low friction and low wear of the components is assured. It should be an autonomic, self-healing system, operating without external interference or help.
The current lubricant additives technology has been analyzed in this paper using TRIZ tools. The aim of the study was to focus on the problem definition stage and to assess how ideal the current technology is. It was also necessary to complete this phase of generic TRIZ process before the selection of the appropriate tools and problem solution.
System operator analysis of the friction process confirms that the system should be considered on different time and scale levels. To ensure desired tribological performance in the present and future stages, action needs to be undertaken in the past in relation to all system levels. Attention needs to be paid especially to the fact, that the super-system and sub-system constituents act simultaneously at the interface, where the tribofilm is formed. The additives technology developed for steel components cannot be used directly to components made of aluminum, for example, as different chemical reactions take place between surface and lubricant additives.
Summarizing the S-curve analysis, there is little scope for the development of the present system; the most likely way to improve the ideality is through the introduction of a new approach. Next generation technology will be characterized by another S-curve, with the initial ideality lower than that for the current system. Nevertheless, it will be on its first-concept stage, from which the ideality will evolve with time.
The IFR analysis suggests that the sought-after solution is a self-lubricating, self-healing, durable and green frictional interface. It brings to mind some analogies with natural systems, which are characterized by these qualities. It has been shown that the combination of TRIZ and biomimetics is a powerful and effective technique for solving engineering problems.13,14 Natural systems attract a lot of attention from engineers, not only due to their sophisticated beauty but mainly because of their high efficiency and durability. There are several examples of successful use of biomimicry for the manipulation of the interface to provide desired functions, such as self-cleaning surfaces based on the surface of the lotus leaf, drag reduction based on shark skin riblets or adhesive surfaces based on nano-structured fibers on the gecko's feet.15,16,17
Tribology is also a discipline that can benefit from bionics engineering. The researchers have already looked at the mechanism of ice friction, bacterial flagellar motor rotary action and frictional characteristics of beetle head-joint material.18,19,20 From the lubrication point of view, the most promising example is the mammalian synovial joint system with its very low friction and long durability.21 The next step for this project is to analyze the synovial joint lubrication mechanism and isolate the processes which can be mimicked in the engineering environment.
Dr. Tomasz Liskiewicz is an Academic Research Fellow in Engineering Design with a broad expertise in the field of materials science. He received his Ph.D. diplomas from the Technical University of Lodz in Poland and from Ecole Centrale de Lyon in France. Since 2005 he has been a member of the School of Mechanical Engineering at the University of Leeds in the UK where he has been appointed jointly by the Institute of Engineering Systems Dynamics and Institute of Engineering Thermofluids, Surfaces and Interfaces. He is actively using a wide range of surface analysis techniques and he has keen interest in the field of biomimetics and TRIZ. Contact Tomasz W. Liskiewicz at T.Liskiewicz (at) leeds.ac.uk.
Dr. Ardian Morina obtained his Ph.D. from the Heriot-Watt University in Edinburgh, U.K., and now holds the RCUK Academic Research Fellowship in the School of Mechanical Engineering/School of Process, Environmental and Materials Engineering at the University of Leeds. His research is focused in the interdisciplinary fields of biomimetics and bioinspiration, tribochemistry, engine tribology and surface analysis. Contact Ardian Morina at a.morina (at) leeds.ac.uk.
Professor Anne Neville has been a chair in Tribology and Surface Engineering in the School of Mechanical Engineering in the University of Leeds since 2003. She is Director of the Institute of Engineering Thermofluids, Surfaces and Interfaces (iETSI), one of three research institutes in the School of Mechanical Engineering. She was awarded the Makdougall-Brisbane prize from the Royal Society of Edinburgh in October 2000 for “an outstanding contribution to engineering science.” In May 2001 she was awarded the Guy Bengough prize from the Institute of Materials for her contribution to the corrosion literature. She is Editor of the new IoM/Maney journal “Tribology – Materials, Surfaces and Interfaces.” She was elected Fellow of the Royal Society of Edinburgh in May 2005, of the Royal Society of Arts, Manufactures and Commerce in November 2005 and of the Institution of Mechanical Engineers in July 2007. Contact Anne Neville at a.neville (at) leeds.ac.uk.
