Optimization of a Heavy Duty Diesel Engine Cam Profiles to Eliminate the Contact Loss using Multi-body Dynamic Model

The design of a cam profile and its effect on the dynamic performance of the operated mechanisms has long been a centre of attention. Cam profile has been known as one of the most important parameters which can directly affect engine performance and the mean gas temperature. Valve timing overlap in turbocharged heavy duty diesel engines can exceed to 120 degrees and even more. In addition, in these types of engine, need for increase the exhaust and inlet valve opening time by dwelling individuates cam design basis of these engines. Two main issues which restrict the cam design are piston strike and maximum negative acceleration which can lead to contact loss. Higher inertia force due to the heavier valvetrain parts in heavy duty diesel engines would increase inertia forces that can aggravate contact loss in system.

In this paper, the valvetrain of a heavy duty medium speed diesel engine under development has been studied. The valvetrain mechanism is modeled by a multi-body system, using ADAMS commercial software, including discontinuities because of the loss of contact between two consecutive components of the valvetrain. The objective is to maximize the area below the valve lift, which has a great influence on the gas flow. Also the contact separation criteria, which are validated by the multi-body dynamic valvetrain model, are discussed in detail. The final generated cam lift ensures the permanent contact without change in spring properties and at the same time preserved engine performance.