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About five years ago, the riding comfort was set after conducting various types of tuning tests. These required considerable man powers and large scale improvement was impossible in wide frequency range. To get large scale improvement and reduce these man powers, an optimum design was needed in the initial stage of development. First, the simulation model of whole vehicle was made to analyze the frequency responce on cab floor and human body when an excited force was added to the front tire. Next, 25 parameters which effected the riding comfort were allocated to L36(211 × 313) type orthogonal array and then 72 simulation analyses were conducted. Of the 25 parameters, 8 were finally selected to be the most effective, after comparing the results with many factorial effect charts. It was confirmed that the test results were well matched with the simulation and all acceleration levels at resonance points fell down over 50%.

Basically, it is recommended that non-linear analysis shoud be used with consideration for friction and etc., when engineers calculate to design the trunnion suspension system for heavy duty trucks. But non-linear analysis was very difficult. so linear analysis per piece parts was conducted under assumed conditions. According to this method, it is difficult to obtain the calculated values matching with experimental values, thus “trial and error” must be repeated consuming much man hours. Recently, accuracy of non-linear analysis has been improved by the progress of the super computer in conjunction with the development of soft-wear such as pre-post or solver. Now, non-linear analysis of the total suspension system was conducted by taking contact and friction between each part into consideration. while at the same time divergence of the solution was prevented by optimum modeling.

Every year the trucking industry demands lighter weight and lower cost truck components. But it is very difficult to achieve both these targets. This paper describes the example of a suspension system design which was conducted by computer simulation, so called CAE. The computer simulation by FEM was used completely to decide the detailed shape of each part. This paper also introduces a casting method to strengthen the aluminum alloy cast using high pressure during casting. By using this method, products have a precise metallographic structure. As a result, both the development cost and period were reduced by over the half the time required of the current system and lighter and strong parts were created.