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

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.