Jean-Louis Ligier

Piston Pin: Wear and Rotating Motion

In new engines, running conditions for piston pin bushes have become very severe due to combustion pressure and temperature increase. Moreover, the lead removal from the bush material has strongly reduced the capability of the antifriction material to accept asperity contacts, geometrical defects or edge loading. Today, it is usual that wear and seizure occur in the piston pin bushes during the first steps of engine development. In order to propose basic design recommendations avoiding damage, during the early steps of engine development, it is necessary to have quick numerical simulations. In these calculations, the mixed lubrication in the piston pin bearings must be taken into account. To obtain a simple realistic tool, a refined contact model is implemented in a simple hydrodynamic lubrication program. Then, the general behaviour of the piston pin is described before focusing on the combustion cycle phases when damage may occur. The oil film thickness variations during cycle are described and show what the critical phases are. Several parameters like pin diameter, temperature, pressure-viscosity coefficient have been investigated in order to understand their influence. To have an efficient wear modelling a special emphasis is put on the description of asperity contacts in order to built a wear model for bearings located on the piston pin. In this wear model, the surface topography parameters are taken into account in order to have a realistic approach and to identify the optimal roughness parameters.

Cumulative Microslip in Conrod Big End Bearing System

High combustion gas pressure and mass reduction of modern automotive engines have generated new problems in mechanical assemblies. For example, it is now common to observe bearing shell rotation in the conrod of automotive prototype engines at the design stage. The consequence is sometimes the seizure of the bearing due to the presence of the joint face relief in the loaded area. Physically, the bearing shell rotation results from cumulated microslip between the bearing and the conrod. To have a better physical approach of the phenomenon and propose design recommendations, we have performed analyses based on the strength of material theory and numerical modellings. These tools permit us to obtain simple models allowing an easier mechanical understanding as well as an analysis of sensitivity to different parameters. The main results presented in this paper are: • The basic description of the phenomenon, • The modelling of the conrod, its sensitivity to deformation and numerical validation, • The analysis of the microslip between the bearing shell and the conrod, • The sensitivity analysis with respect to conception and physical parameters.Copyright

Fatigue Analysis of Conrod Bearing

1) Abstract For many years, bearing suppliers use efficiently the specific pressure to evaluate the fatigue risk of conrod bearings. However, modern engines have made the bearing more sensitive to various phenomena such as the thermal expansion or the elasticity of the conrod housing. These effects modify the stresses in the bearing layers and by the way the fatigue loading. In this paper, we analyze the elastic and plastic behavior of the bearing during the engine life. We detail and provide the analytical relationships, which determine stresses in the overlay and the substrate of the bearing. Various loadings are taken into account such as the thermal loading, the hydrodynamic pressure field, the fitting loading, the free spread loading. The knowledge of the relationships helps to understand the mechanical behavior of the bearing. Particularly, it allows demonstrating that plastic flow occurs in the substrate and in the overlay during the first combustion cycles and the first thermal cycles. Residual stresses are introduced by plastic flow and modify the stress tensor in the different layers. Therefore, the two layers are subject to high cycles fatigue (H.C.F.) with combustion cycles and low cycles fatigue (L.C.F.) with thermal loading. The high cycle fatigue analysis is performed with multiaxial criteria.

Cooperation and cooperative design for a new automotive engine in the Renault group

To develop a new engine, many contributors are involved in the design process, particularity when the car manufacturer is an international company. The presentation will give in a first part an overview on cooperation between various Renault members. After a description of main difficulties to exchange, we will focus on the main keys to success. A second part will be dedicated to the internal collaborative works within Renault corporate. It will be related to the different physical area which define or constrain the engine design. As a new engine is the results of many optimizations between different domains of physics, the process to get these optimizations will be described. Some focus will be given on the main difficulties encountered to get cooperative design. To finish, perspective on improvement will be mentioned.