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A method of fatigue life prediction of spot welded joint under multi-axial loads has been developed by fatigue life estimation working groups in the committee on fatigue strength and structural reliability of JSAE. This method is based on the concept of nominal structural stress ( σ ns) proposed by Radaj and Rupp, and improved so that D value is not involved in stress calculation. The result of fatigue life estimation of actual vehicle with nominal structural stress which was calculated through newly developed method had very good correlation with the result of multi-axial loads fatigue test carried out with test piece including high strength steel.

Ceramic materials such as silicon nitride and sialon are known for their excellent wear-resistance and scuffing-resistance even under high contact pressure and poor lubrication1. However, ceramic materials, which have excellent sliding properties, are not widely adopted for valve train components, at present. A main reason for this is their high cost. A ceramic cam follower, newly developed by utilizing the direct brazing technology, has the following features and can be produced at the lowest cost: (1) Parts are only three. -A thin ceramic disc, a steel body, and an active brazing foil. (2) No grinding is necessary after brazing. -A crowning at the cam sliding surface is formed by the difference of the thermal expansion coefficients between silicon nitride and steel. (3) No hardening is necessary after brazing. -The steel body is hardened by the heat treatment of brazing.

This paper describes the development of an inexpensive ceramic cam follower that uses a silicon nitride material and is more wear and scuff resistant than the sinter alloy cam follower. A thin ceramic disk is directly brazed on a steel cam follower body without using any stress-relief materials which makes the grinding for crowning unnecessary, reducing the production cost. We performed a material screening test using an abrasion tester to determine the optimum type of silicon nitride and the optimum surface roughness. Engine endurance tests proved its excellent wear and scuff resistance. Consequently, it has been adopted in the 1993 series production engines as the first ceramic cam follower.

This study establishes the feasibility of improving the motion characteristics of commercial vehicles by applying rear axle steering. A model-matching control algorithm for rear axle steering was used to achieve the desired yaw rate response to steering action. Simulations with a two-degree-of-freedom model evaluated the effectiveness of the control method. Results of vehicle tests on an experimental medium-duty truck with rear axle steering proved that this control method can improve vehicle yaw response. However, the simulation results did not well represent the vehicle test results, because the simulation model was too simple. Adding the roll effect to the model reduced the discrepancy between the simulation and vehicle test results.

Because of smaller ratios of tread to height of gravitational center, longer wheel-bases, and larger moment of inertia, vehicle roll is the most important characteristics governing truck controllability and stability. And longer wheel-bases result in a reduction in vehicle body torsional stiffness. Hence, the influence of vehicle body torsional stiffness on vehicle roll characteristics is investigated. We carried out a simulation analysis and vehicle test on medium-duty trucks, in studying the vehicle frequency response characteristics by changing vehicle design parameters. The results show that a reduction in body torsional stiffness increases the steady state gain of the front roll angle without affecting the yaw and lateral characteristics of vehicle motion. Accordingly, even if body torsional stiffness is unavoidably lowered, reducing the front roll angle by increasing the roll stiffness of the front suspension can maintain appropriate vehicle controllability and stability.