This paper gives the General Motors (GM) perspective in vehicle tribology. Tribology plays an important role in vehicle durability, reliability, and fuel efficiency. While several areas in the vehicle are included, major emphasis is given to engine tribology. Piston skirt, piston rings, crankshaft and its bearings, and the valve train are identified as the most critical reciprocating engine components for tribological investigation. In addition to discussing these, engine friction, engine lubricants, clutches and brakes, and sheet metal forming are briefly covered. In each case the tribological state-of-the-art, as applied in design, is identified. GM's analytical and experimental capabilities are discussed, and areas where more work is needed are identified.

A new computational model, using the finite element method for both fluids and solids, is presented for transient elastohydrodynamic lubrication analysis. The relative (differential) displacements of lubricated surfaces are represented by linear combinations of selected modeshapes, which form an acceptably adequate basis for both relative rigid body displacements and relative elastic deformations. The model combines both elastostatic (solid) and hydrodynamic (fluid) aspects in a single coupled initial value problem of relatively low order. A case study of an idealistic bearing structure is presented to explain fully the detailed workings of the new computational model, which is subsequently applied to a realistic automotive connecting rod to demonstrate its versatility and accuracy.

The elastohydrodynamic lubrication of an automotive piston was analyzed. The important effects of thermal and pressure distortions were demonstrated by analyzing two piston skirts which have different axial profiles but are otherwise identical. Results show that a significant reduction in friction can be realized.

An approximate method for solving the elastohydrodynamic (EHD) lubrication problem has been developed. The method is based on two assumptions: the separation of variable for pressure and a parabolic pressure distribution in the axial direction. To solve the governing equations, the Newton-Raphson method, in conjunction with Murty’s algorithm, is used. The finite-element and the finite-difference methods are then used to obtain approximate solutions. The rod bearing of a typical connecting rod is analyzed by the new method. The results are compared to the full EHD solution and the rigid bearing solution. Significant reduction in computation time is realized when compared to the full EHD solution.

The effect of support structure on the performance of a connecting rod bearing is analyzed by elastohydrodynamic lubrication theory. The support structure is modified iteratively until an optimum design is obtained. With the connecting rod of a typical gasoline engine as an example, it was found that a 150 percent improvement in film thickness and a 34 percent reduction in peak pressure can be obtained by changing the structural design. This design, however, increases the peak octahedral shear stress in the rod. Structural design changes considered were found to have surprisingly little effect on the power loss of the bearing.

The Newton-Raphson algorithm was used in conjunction with Murty’s algorithm and the finite-element method to analyze the elastohydrodynamic lubrication of a journal bearing under dynamic loading. Cavitation boundary conditions were used. A realistic compliance matrix and load schedule were used in the illustrative example. Solutions for the film pressure, the film thickness and its rate of change with time were obtained as functions of the crank angle.

The mobility method of solution is frequently used for analyzing dynamically loaded journal bearings. Curve fits of journal-bearing solutions are used in this method. All the currently available curve fits are lacking in one or more of three important features—the solution accuracy, the solution detail, and the solution time. A new set of analytical curve fits is presented in this paper. The set includes: the two components of mobility vectors, location and magnitude of maximum film pressure, and the starting and finishing angles of the pressure curve. For an ideal journal bearing, the new curve fits give accuracy and solution detail comparable to an expensive finite-element analysis, while keeping the solution time comparable to that required for the short-bearing approximation. An example is presented to demonstrate the use of the new curve fits.

In this paper a finite element formulation for transient analysis of journal bearings is described. The formulation can be used for partial or full-arc bearings with oil-supply hole and oil-feed grooves, with tapered or misaligned journal, and with elliptical or eccentric bearings. An important feature of this analysis is relatively low computing cost. The analysis is followed by an illustrative example in which 17 different cases of a connecting-rod bearing are solved.

This addendum informs the reader on additional references on multiple offset bearings from the Japanese literature

The finite element formulation for regular cylindrical bearings is extended to include irregular (noncylindrical) bearing surfaces. The optimum bearing shape is sought for a specific duty cycle with a constant load and sinusoidal angular displacement. The optimization is done with a view to maximizing the minimum film thickness. For the purpose of optimization a one-dimensional cylindrical bearing is considered. The optimum among all elliptical shapes is found to combine a specifically elliptical sleeve and a perfectly circular journal. For this optimum noncylindrical bearing the absolute minimum film thickness is about a factor of 36 higher than that for the corresponding regular bearing. The absolute maximum pressure for the optimum bearing is about a factor of 5 lower than that for the regular bearing.

Novel “offset” designs offer greatly improved durability and reduced power loss in applications for which conventional journal bearings are only marginally satisfactory. They are particularly attractive for duty cycles which combine nonreversing loading with limited angular oscillation. Production applications presently include piston-pin / cross-head bearings for two-stroke Diesel engines. The present analysis combines impedance concepts with a generalized short bearing film model for partial arc bearings. A numerical example compares performance of offset and conventional designs for a specific application.

Analytical solutions are not available for spherical bearing problems except for very specialized cases. However, the finite element method presented here can be used to analyze virtually any such bearing having an incompressible lubricant between surfaces which are smooth, rigid, and impermeable. The method can be easily extended to account for permeable surfaces and lubricants with variable viscosity and density. Triangular finite elements with linear interpolation functions are used to model the lubricant film. For complete films an elimination method solves the resulting system of equations; for incomplete films an iteration scheme incorporates Reynolds boundary conditions. The method is extended from “direct” (explicit) problems of specified planar motion to “indirect” (implicit) problems with specified planar loads and can be further extended to solve these problems with general spatial motion and loads. The results for spherical bearings are similar in trend to those for cylindrical journal bearings and suggest the former as possible alternatives, especially if axial as well as radial forces are present.