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Technical Paper

Development of Intake Sound Control Technique for Sports-Type Motorcycles

Engine sound is one of the most important factors when selecting a motorcycle from various models. Therefore, it is necessary to create an appealing sound in the rider's ears in addition to complying with noise regulations. In this paper, how we control intake sound is described through the study of a sports-type motorcycle with an inline 4 cylinder engine. To control intake sound, both intake pressure pulsations generated by the engine and acoustic transfer characteristics of the intake system are important. It is shown by unsteady-state one-dimensional computational fluid dynamics analysis that specifications of the exhaust system affect intake pressure pulsations across the valve overlap period. Therefore, to emphasize high order components of the engine revolutions in the intake sound, for example, modifying the layout of the exhaust muffler is effective.
Technical Paper

Development of Fail-safe Method for Motorcycle's Electronic Throttle Control System

In recent years, even motorcycles impose demands for engine power controls that are more flexible and precise. The Electronic Throttle Control (ETC) system is one of the methods that addresses this need. However, the most important issue facing the installation of the ETC system on the motorcycle is handling failures. To avoid this problem, we developed an ETC system for motorcycles that can properly effect engine power control in case of a failure. This ETC system contains in duplicate the major components to detect failures and switch to a failure mode properly. To effect control that is optimally suited to the type of failure, this system switches between three types of failure modes. These failure modes are designed to minimize risks in case of a failure and maximize the operational capability while the rider is on the way to have the motorcycle repaired.
Technical Paper

Development of a Magnesium Swing Arm for Motorcycles

In order to improve the fuel efficiency and the operating performance of motorcycles, there is a need to reduce their weight. Magnesium, which is the lightest of the various metals currently being used and has a high specific strength, has the potential to satisfy that need. We conducted a study to clarify the weldability and strength characteristics of, and the most suitable surface treatment for, extruded magnesium alloys and rolled magnesium alloys. Based on the stress analysis by the finite element method, we designed a magnesium swing arm and produced the prototype swing arm by pressing hot rolled AZ31 magnesium alloy plates and welding them. The prototype is about 10% lighter and has higher torsional rigidity than a conventional aluminum swing arm.
Technical Paper

Analysis of Disk Brake Squeal Using Substructure Synthesis Method

This paper describes a numerical analysis method for predicting the brake squeal using the Substructure Synthesis Method. This method is more accurate than the classical method based on the mass-spring system, and simpler than the analysis of all the brake system by FEM. The squeal studied here is focused the one occurring in the low frequency range and its mechanism is due the structural instability of the brake assembly. First, some experiments were carried out in order to grasp the brake squeal phenomenon. These experiments made clear the following items. (1) The low frequency brake squeal occurred at 850Hz. (2) The vibration mode shape had 5 nodes fixed in a space. (3) The brake squeal became maximum at 0.3 - 0.5 (MPa) liquid pressure under the constant temperature condition. (4) The higher the temperature of the pad was, the stronger the brake squeal was under the constant liquid pressure condition.
Technical Paper


Motorcycle engines are operated at an extremely broad range of revolutions, from 1000 min-1 to 10000 min-1 or more. Ideally, the natural frequency of each part should never match the engine excitation frequency at any point over that entire range of revolution speeds, but practically, there are times when resonance cannot be avoided because the range is so broad, and therefore the vibration amplitude at resonance must be kept low. For this reason, it is important to grasp not only the resonance frequency but also the vibration amplitude at that point. This may be achieved by two methods, measurement and analysis. The direct measurement of vibration is generally difficult because the motorcycle muffler system has a complex shape and in addition it gets very high temperature when the engine is operating. For this reason, with the aim of being able to predict muffler vibration at the design stage, we carried out a vibration test and FEM (finite element method) analysis.
Technical Paper

Prediction of Transmission Loss for Motorcycle Muffler

This paper describes the predicted results of acoustic transmission loss (T.L.) for a motorcycle muffler. First, the T.L. of a prototype muffler with one expansion chamber was obtained by measuring sound levels at the inlet and outlet ports of the muffler by speaker test. T.L. was then calculated by using a three-dimensional Finite-Element Method (FEM) for acoustic fields in the muffler. There was good coincidence between the calculated T.L. and experimentally observed data. Second, T.L. of the prototype muffler while attached to a motorcycle engine was measured. On this step, however, a similarly calculated T.L. using FEM to consider the effect of exhaust gas temperature in the muffler showed differences from the measured one. It was estimated that muffler body vibration sounds may affect the result. A dynamic analysis of the structure was carried out using FEM to obtain the eigen modes of the muffler body.
Technical Paper

Evaluation Method of Exhaust Sound Quality of Motorcycle

The quality of exhaust sound has become one of the important factors in the motorcycle market. Therefore both an efficient sound quality evaluation method and technology to achieve ideal sound quality have become necessary. Sound qualify evaluation has generally been performed by trial and error through repeated modification of exhaust silencer construction until desired quality was obtained. But it usually took painstaking work and long hours. In order to solve such problems, we established an objective auditory evaluation method. We also applied Principal component analysis to analize the result of the “Semantic Differential Method (SD method)” so as to determine the affecting elements. Through this analysis system, “powerful sound” caused by relatively higher content of the low frequency range and “crispy sound” caused by a cyclic sound pattern were determined to be desirable sounds for “American type” motorcycles.