Ensuring the operationality of connecting rod bearings of the KAMAZ–740 automotive diesel engines



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Abstract

BACKGROUND: Unacceptable shape changing of the liners, which have been studied quite fully with regard to influence of changing the geometric parameters on their technical condition, but the factors causing such a process are not fully described, is a special one among the causes of operational failures of connecting rod bearings of automotive diesel engines crankshafts.

AIM: Improving the reliability of automotive engines by eliminating the shape changing of crankshaft connecting rod bearing liners in operation.

METHODS: This paper summarizes the results of studies of the performance of connecting rod bearings of the KAMAZ–740.10 automotive diesel engines under bench test conditions using original methods. The results are obtained from ongoing exploratory research work using original proprietary methods using laboratory equipment of the manufacturer and test objects, modified and prepared to obtain data under standard and limiting conditions. Decrease in protrusion and straightening, which determine the stressed state of the liner in a bed, and deflection along the generatrix, which violates the cylindricity of the bearing and reduces the actual clearance in the bearing, acting simultaneously as a single process are the study object.

RESULTS: The paper presents the results of comprehensive studies of factors contributing to the development of deformations of connecting rod bearings under the influence of a stressed state in a steel base, taking into account various temperature conditions and conditions for supplying oil to connecting rod bearings. It has been found that stresses in the steel base of the liners are formed during their manufacture, during stamping and pouring, to which the stresses from installation and temperature gradients in the bed during diesel operation are then summed up. The ongoing process of stress relaxation in the steel base when the stress is excessive causes the decrease in the performance of the liners. The liners change their initial stress state and geometric parameters (protrusion and straightening), and relaxation takes place within 180–200 running hours of engine operation at nominal mode, after which the intensity of the change approaches zero. Data on significant temperature gradients of the steel base of the liner in the bed were obtained: the temperature difference between the inner and outer surfaces of the liner can reach from 60 °C to 80 °C, and between the liner and the connecting rod – from 50 °C to 70 °C, which causes the formation of additional compressive stresses and associated shape changes of liners. Deformations lead to shape changes of the working surface and to a violation of the oil layer, as well as to direct contact of the liner with the neck due to deflection sampling, gripping of surfaces and turning of the inserts.

CONCLUSION: The new results obtained on the process of decreasing the performance of connecting rod bearings due to shape changes make it possible to optimize the design and operational parameters of crankshaft bearings and lubrication systems of automotive diesel engines. Examples of innovative design solutions for connecting rod bearings with high resistance to deformation are given.

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About the authors

Vyacheslav N. Nikishin

Kazan Federal University

Email: VNNikishin@kpfu.ru
ORCID iD: 0009-0004-3880-9419
SPIN-code: 6978-1196

Dr. Sci. (Engineering), Professor

Russian Federation, Kazan

Ruslan F. Kalimullin

Kazan Federal University

Author for correspondence.
Email: rkalimullin@mail.ru
ORCID iD: 0000-0003-4016-2381
SPIN-code: 3492-4311

Dr. Sci. (Engineering), Professor, Head of the Automobiles Department

Russian Federation, Kazan

Alexander T. Kulakov

Kazan Federal University

Email: alttrak09@mail.ru
ORCID iD: 0000-0002-6443-0136
SPIN-code: 6745-0764

Dr. Sci. (Engineering), Professor

Russian Federation, Kazan

References

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Supplementary files

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2. Fig. 1. Scheme of development of shape changes in connecting rod bearings with increasing deflection: 1: connecting rod, 2: bearing, 3: crankshaft; а: initial state of the connecting rod bearing without deflection; b: initial phase of deflection development; c: phase of the maximum permissible deflection of the liner; d: phase of maximum deflection of the liner; S1, S2, Sп.д, Sп : deflection measurements corresponding to the phases of development of shape formation.

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3. Fig. 2. Installation of thermocouples in the liner and connecting rod: points 1…18: thermocouple installation points; ω: direction of shaft rotation.

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4. Fig. 3. Temperature distribution diagrams in thermocouples installation points on the working and outer surfaces of the upper and lower connecting rod tabs: I: upper liner; II: lower liner: 1: idle speed at 2930 RPM; 2: nominal mode at 2600 RPM.

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5. Fig. 4. Changes in the temperatures of the working surfaces of the liners and oil parameters according to full-load characteristic: tшн; tшв; tкн: average temperature of the connecting rod lower, upper and lower main liners; tм; pм; Qм: average temperature, pressure and oil consumption.

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6. Fig. 5. Change in the temperature of the working surfaces of the liners from the oil temperature at the inlet to the main bearing when the engine is operating in nominal mode; tшв; tшн; tкн: temperature of the connecting rod upper and lower, and main lower liners.

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7. Fig. 6. Change in the temperature of the working surface of the liners from the oil pressure at the entrance to the main bearing at oil temperatures of 70°С and 110°С when the engine is operating in nominal mode; tшв; tшн; tкн: respectively, the temperature of the connecting rod upper and lower, and main lower liners.

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8. Fig. 7. Scheme for determining pressure losses in the crankshaft channels due to the action of centrifugal forces and outflow modes from the connecting rod cavity: 1: tube from the channel along the axis of the crankshaft; 2 and 3: tubes from the connecting rod cavity; 4: slink.

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9. Fig. 8. Profile diagrams of the working and outer surfaces of the liners and connecting rod along the generatrix depending on engine operating hours during reliability tests: I: upper bearing liner; II: lower bearing liner: 1: connecting rod; 2: outer surface of liner; 3: working surface of liner; 4: working surface of liner; 5: outer surface of liner; 6: connecting rod cover.

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10. Fig. 9. Shrinkage of geometric parameters of connecting rod bearings during testing: ∆─∆: upper liner; ○─ ─ ○: lower liner; 1: protrusion h; 2: straightening Dсв.

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11. Fig. 10. Stress diagrams in the cross-section of the liner due to the liner tension (а), from the reduction in straightening (b) and the total assembly and thermal stresses (c); σс: stresses from compression; σи: stresses from bending; σТ: thermal stresses; σ: total stresses; b: liner width.

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12. Fig. 11. Diagrams of stresses in the liner due to temperature changes (а, b) and total assembly and thermal stresses (c); σDt1, σDt2: stresses, respectively, from the temperature gradient along the thickness of the liner and between the liner and the bed; σс: compressive stress; σТ: thermal stresses; b: liner width; Δb: liner width extension.

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