Engine development, driven by environmental considerations outlined in the different emission regulations, fuel economy, and fuel availability in combination with economical boundary conditions, needs new approaches in bearing material and design. Since gas engines are gaining market share and firing pressures increase in diesel engines in order to fulfill fuel economy, a special focus has also been taken to tailor-made bearings for these applications. This complex task has to consider lining compound material strength and stability under different conditions like oil condition and dilution. Thin overlays with long-term wear resistance and mixed friction capabilities as well as robust design for extraordinary events like dirt shock loading or adaptations at the engine start are neces sary. To fulfill all these requirements, different tasks have to be considered: (1) bearing lining and steel shell compound to fulfill assembly requirements to combine a safe bear ing seat with antifretting and high strength with base tribological characteristics, (2) design and use of different layers to compensate weakness of the one layer with the strength o f another layer, (3) incorporation o f special running conditions and cost reduc tion approaches in the layer design like polymer coatings for start stop and shaft designs with rougher surface finishes, and (4) bearing design incorporating special shapes to cope better with deflections and geometric deficiencies of a special engine design or application In this publication, existing and new lining compound approaches, includinglead-free designs, a variety of different overlays from electroplated, polymer and sput tered ones, are briefly described. Additionally, it is explained how these layers are com bined and how they work together to improve bearing performance. Testing of the bearing components and designs on bearing test rigs with new test conditions considering dirt shock and misalignment and their confirmation by engine running experiences are given for a gas engine and a high speed diesel engine applications. A special outlook on how this approach can be extended to other applications for the sake of robustness, cost reduction, or performance increase will summarize the paper.
The development of combustion engines is heavily influenced by environmental regulations and efficiency. Since the environmental regulation have influenced engine design already with special combustion system and exhaust gas treatments, efficiency and the greenhouse gas CO2 has become a major issue for further development. CO2 emissions and fuel efficiency are linked and are directly influenced by the internal friction of the combustion engine. One major part of this internal friction is coming from the crank train bearings. Since we have to consider different operating conditions for the crank train bearings like hydrodynamic and mixed friction (hydrodynamic in combination with boundary contact), working principles as well as different engine operating conditions like full load, idle, start stop etc. different measures need to be employed for a friction reduced crank train. The optimal dimensioning of the bearings in combination with oil viscosity reduction are already known to a certain extent. Nevertheless they result in changes of bearing loads and may in consequence increase the share of boundary friction. Therefore, only looking on these two optimization steps is not enough. In addition the friction coefficient between bearing and shaft as well as the interaction between bearing surface and lubricant need to be addressed to reduce friction loss. In order to gain a complete picture, influences and the interaction of • geometric properties and bearing dimensions, • friction coefficient of bearings in combination with crankshaft materials, • oil formulation, viscosity and their interaction with engine application and duty cycle as well as • losses caused by the lubrication system design and components are investigated and analyzed based on simulation and testing. At first the different steps are investigated individually and secondly combinations and interactions are derived on basis of parameters derived on tribological tests and material data. Oil viscosity as major driver during hydrodynamic operation but also the influence of additive packages during mixed friction is roughly estimated on basis of tribological investigations. Since the overall friction system and its optimization are very complex, an example for a truck engine in different applications shows advantages and disadvantages of the different approaches. Also border lines given by operational risk and improvement limits are explained. The improvement options given by bearing materials and special coatings are explained in combination with different engines and engine applications. Further development activities, ways of collaboration between engine manufacturer and bearing supplier and an outlook on up-coming bearing system are completing the picture for a holistic approach on friction reduction in crank train bearings.
Due to strict lead recycling regulations put upon discarded automobile engines, removing lead from new automotive engines became essential. Removing lead found in batteries from discarded automobiles is fairly straight-forward and inexpensive; however, much labor and cost is associated with removing lead containing engine bearings. Due to the relatively light loading applied to automotive gas engine bearings, lead-free aluminum alloys have been developed. Many experts predict that this lead-free trend will carry over to non-automotive bearings as well. Many of these non-automotive engines are run on diesel fuel and have much higher loading on the bearings. The current generation of lead-free aluminum alloys just cannot carry the loads required by these engines. Therefore, there has been efforts on developing lead-free copper based bearing alloys. This paper reviews one process that was undertaken to develop lead-free copper based alloy to be used in these highly loaded, non-automotive lead-free engine bearing types. This process included a fundamental understanding of the tribological role of lead in copper based bearing alloys, as well as a thorough performance screening of lead-free bearings types based on this lead-free lining and a comprehensive review of the test results. Also included in this paper are some future development plans in the world of lead-free copper based bearings alloys.
A new concept for bimetal bearings combining the development of a new bearing alloy and the bearing type design as a composition of different layers is presented. The goal was to reach the performance of typical trimetal bearings by the economical solution of a bimetal bearing design. An intensive study of performance shortages of today’s conventional bimetal bearings as well as a scope of future bearing performance needs headed the performance description of the newly developed bearing type. Metallurgical and technological options given in the publication were used to reach the design criteria. The development resulted in an aluminum bearing alloy with increased tribological and mechanical properties including a special bearing type design with a high strength bonding layer. The roll bonding procedure was adapted to produce the steel aluminum strips. As an important part of the development, resistance against corrosion and cavitation were taken into consideration. The reported results from test rigs and field tests in different engines demonstrate that the original expectations have been fully achieved. Hence, the economical advantage of bimetal bearings versus trimetal design can be realized.
This paper presents experimental performance characteristics of fixed-geometry hydrodynamic thrust bearings machined to different helical taper depths. Theoretical analysis based on the Reynold’s equation states that under favorable conditions, these taper depths can produce and maintain load-supporting hydrodynamic pressure yet result in characteristically different oil-film pressure distribution profiles and magnitudes of friction torque. These characteristic performance indicators have not previously been observed experimentally for unidirectional fixed-geometry hydrodynamic thrust bearings with helically tapered pads. An experimental test rig was developed by re-purposing a horizontal milling machine capable of subjecting the test bearings to speeds up to 1,265 rpm and axial loads up to 250 lbf (1,112 N). Under various combinations of constant speed, load, and lubrication supply conditions, the steady-state oil-film pressure distribution across the bearing pad and active friction torque are measured. The effects of variable taper-depth on hydrodynamic pressure distribution and friction torque are compared and discussed.
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