Abstract
This paper deals with an optimal control of non-linear mechanical system. In this method, the functional consists of total energy of controlled system, performance function and energy function. This energy function is described by energy flow which is transmitted from controller to controlled system. The functional is described as a first-order expression concerning with control variables, therefore it is able to induce optimal control law from the condition of minimising the functional. This method was applied to the control problems of the energy regenerative active suspension.. As a result, it is clarified that this method is useful to design controllers for energy regenerative control systems. In continued reports, it is shown that this method is applicable to nonlinear mechanical system and nonholonomic system.