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All the primary inertia forces and/or moments generated by engines having three cylinders or less are not normally in balance by themselves and thus may be a great source of vibration for the frame supporting the engine. If the mass distribution of the crankwebs is selected in a proper manner, it is possible to determine arbitrarily the directions and the length ratio of principal axes of ellipses, which are obtained as Lissajous diagrams of inertia force and moment. This method can be effectively applied to reduce vibration in the frames. In this paper the appropriate inertia force and moment ellipse equations are developed and the analysis is outlined for optimizing the engine balance. Also the fundamental properties of the linear vibration systems excited by the elliptical forces as well as some experimental examples of elliptical excitation are detailed.

We introduce a research on steering dampers using MR fluid (Magnetorheological Fluid). In recent years, steering dampers have been used in on-road and off-road motorcycles. Steering dampers stabilize the front end of motorcycles. The advantage of a steering damper is increased stability, but hydraulic steering dampers give rise to the problem of ‘Heavy Steering’. In order to resolve this heavy steering, we need to set the restrictions on the maximum damping force and avoid it from interfering when the rider is steering. However only reducing the damping force will lead to insufficient damping force when the handle, unresponsive because of kickback, shakes. We solved this problem with the development of an electric control damper which generates sufficient damping force at low steering angle rates and also allows for mechanically limiting the maximum damping force.

In this paper, we introduce a research of Steering Damper using MR fluid (Magnetorheological Fluid). In recent years, Steering Dampers have been used in motocross races on off road courses. Steering Dampers stabilize the front end of motocross bikes that are used in competitive races held on rough terrain. The advantage of a Steering Damper is increased stability, however hydraulic Steering Dampers give rise to the problem of ‘Heavy Steering’. In order to solve this problem, we used MR Fluid and developed an Electronic Control Steering Damper that does not use a valve like hydraulic damper. The damper design uses “Direct Shear Mode” and features a steering angle sensor built into the damper, which results in easier, smoother steering. To test the effectiveness of our new design, we installed our new Steering Damper on the YZ 450F (Yamaha's competition model). We then asked for feedback from riders both in Japan and overseas.

This paper covers certain aspects of the 2-stroke cycle, high-speed, high-output racing engine developed by Yamaha. Based upon design concepts and data from the development of the general racing engine, as well as the development of Grand Prix racing engines, this material is especially concerned with intake, scavenging, and exhaust systems. In addition, data on cooling and lubrication systems are presented.

The propeller blade hydrofoil section is one of the factors that determines the propeller performance. In the development of the hydrofoil, repeatedly performed experiments using many foil models and the cavitation tunnel involve extended time and high cost. This is why there are expectations for the numerical simulation to realize shorter development time and cost cutback. On the other hand, a technique for reproducing the hydrofoil characteristics taking account of the cavitation effect using CFD (Computational Fluid Dynamics) has hardly been established. There is no example of performance prediction especially for a hydrofoil section of the outboard motor propellers in which the trailing edge is cut off. This paper describes the results of the prediction of hydrodynamic characteristics performed in regard to the two differently shaped outboard motor propeller blade hydrofoil sections taking account of the cavitation effect.

A high-quality die-casting technology has been developed for lightweight aluminum frame structures that produces high-strength aluminum parts that are also weldable. This new technology has been used in casting frames for motorcycles and snowmobiles and has enabled improved frame designs with far fewer component parts than was possible before. This die-casting technology also results in a significant reduction in energy consumption during the manufacturing process.

A laser Doppler velocimeter is used to measure in real time the velocities of pipe flows in a crankcase-scavenged small two-cycle engine with piston and reed valves. Consequently the optical windows in each pipe must be exchanged instantly by using rotary window systems. The flows in both the inlet and exhaust pipes show different patterns in the motored and firing conditions, but the flows in the scavenging pipe are in a similar pattern regardless of the operating conditions.

This paper describes the development of a new concept two-wheel steering system for realizing motorcycle motion control. By considering the whole of the main frame as the rear-wheel steering axis, it was possible to move the rear-wheel steering system from the conventional installation position at the rear arm to the head pipe. As a result, the developed two-wheel steering system is both lightweight and compact. This two-wheel steering system was installed in a motorcycle, and starting and stopping tests were carried out with two people riding on the motorcycle. The test results confirmed that the two-wheel steering system is capable of changing the motion characteristics of the motorcycle in actual riding. Furthermore, by calculating the equivalent wheel alignment of this system, this paper also theoretically demonstrates that these changes in motion characteristics are caused by changes in caster and trail.

A connecting rod made of titanium alloy is effective for lower fuel consumption and higher power output comparing to a steel one because the titanium connecting rod enables to reduce the weight of both of reciprocating and rotating parts in an entire engine substantially. But up to now, it has been adopted only to expensive and small-lot production models because a material cost is high, a processing is difficult and a wear on a sliding area should be prevented. In order to adopt the titanium connecting rods into a more types of motorcycles, appropriate materials, processing methods and surface treatment were considered. Hot forging process was applied not only to reduce a machining volume but also to enhance a material strength and stiffness. And the fracture-splitting (FS) method for the big-end of the titanium connecting rod was put into a practical use.

The fracture splitting (FS) method for case hardened connecting rods has been developed to improve engine performance while decreasing production costs. The FS method is widely used for automotive connecting rods because it effectively improves their productivity. Normalized forging steels, microalloyed forging steels and powder metals have generally been used as the material in the FS method as they are easily split due to their brittleness. On the other hand, the materials to be used for high performance motorcycles are case hardened low carbon steels because they allow the connecting rods to be lightweight due to their high fatigue strengths. These materials, which have a hardened area of approx. 0.5mm in depth from the surface, have a ductile texture inside. This texture obstructs the crack propagation and makes the split force too high to split without deforming the bearing area.

Generally, the gearshift mechanism for outboard motors shifts into forward or reverse gear without using the synchromesh arrangement (dog clutch engagement)(See Fig.1). This type of shift mechanism has advantages in simple structure and in saving space and cost, but at the same time, this is often the source of problem due to the abrasion caused by the hitting of gear against the dog clutch before the engagement, as well as large gearshift shock and noise. In addition, the outboard motor horsepower is getting bigger in recent years. As they are equipped with bigger and heavier engines and propellers, the shifting shock and noise tend to become more severe. For this reason, the improvement in this aspect is required. We looked into the way to reduce the shock and noise by means of propellers, because the propeller can be mounted and replaced easily, which allows the effective improvement to be spread to the outboard motors already in the market.

In four-cycle single-cylinder motorcycle engines, high Hertzian stress is generated on and beneath the big-end surface of the connecting rod. If the surface strength would be improved, the diameter of the big-end could be made smaller, making the entire engine smaller and lighter. Therefore, application of carbide dispersion carbonitriding using a vacuum furnace (hereinafter referred to as “vacuum CD carbonitriding”) on the big-end surface was investigated. Vacuum CD carbonitriding was carried out by three processes. The first was a CD carburizing process. This process is done to obtain granular cementite, but in order to avoid decreasing the strength, it is necessary to prevent the formation of coarsened cementite at the grain boundary. The second process was a refining process. This process is done for the purpose of refining the prior austenite grain size. The third process was a carbonitriding process.

This paper presents an approach for efficiently evaluating motorcycle main frame strength using external loads predicted from measured strain data in our development process. The loads are calculated by simple matrix inversion, and can be used as boundary conditions of static analysis that resembles actual phenomena. The advantage of this method is that it allows relatively precise reproduction of actual boundary conditions without the data usually needed for dynamic simulation such as tire and suspension characteristics which often take large amount of time and man-hour to obtain. Although this approach is simple and common practice, there are a lot of things to be concerned for gaining useful results in a broad range of stages in the motorcycle main frame development process. How we effectively make use of this approach is going to be introduced here.

Regarding S.I. gasoline engine, it is one of the most important matters to eliminate cyclic variation of combustion. Especially with high compression ratio and high boosted engine, the difficulties increase more. This paper describes the analysis of combustion process precisely by using many ion-current probes and CFD with the unique approaches. The number of used ion-current probes is 80 and they are mounted on whole combustion chamber wall especially including moving intake and exhaust valve faces. Thus cyclic variations of flame propagation can be measured precisely under high compression ratio and high boosted conditions in a multi-cylinder engine. In addition, CFD combustion simulation is conducted through full four strokes of continuous nine cycles. Moreover air motion and pressure vibration in intake and exhaust manifolds in whole cycles are considered. These unique approaches have made CFD result correspond to the measurement result of cyclic variations of actual combustion.

Connecting rod design factors, such as geometric shape, capscrew torque and materials can significantly affect bore distortion and assembly stress. In this paper, experiments using different materials were conducted on several connecting rod big-ends with various shapes, bosses and bolts. The results show that the distortion of the big-end bore and the bolt stress are influenced considerably by the big-end shape, the bolt axial tension and the material under inertia force. It was also observed that the bolt bending stress and the load separating the big-end joint surface could be calculated with high accuracy using three-dimensional FEM in the initial connecting rod design.

A direct injection system in which fuel was injected through the cylinder wall was developed and detailed investigation was made for the purpose of reducing short-circuit of fuel in 2-stroke engines. As a result of dynamo tests using 430cc single cylinder engine, it was found that the injector was best attached at a location as close to TDC as possible on the rear transfer port side, and that the entire amount of fuel should be injected towards the piston top surface. Emissions were worsened if fuel was injected towards the exhaust port or spark plug. Although the higher injection pressure resulted in large emissions reduction effects, it did not have a significant effect on fuel consumption. When a butterfly exhaust valve, known to be effective against irregular combustion in the light load range, was applied, it was found to lead to further reductions in HC emission and fuel consumption while also improving combustion stability.