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YAMAHA Motor has developed and marketed a hybrid bicycle with an electric supplemental power source which generates assist power in proportion to the pedal torque by riders. The key function required for this assist power control system is that the variation of the assist ratio should be as small as possible over wide range of riding conditions. The assist power control system consists of mechanical and electrical components and requires a very tight quality control of each component if the design fails to be robust to disturbances such as pedal torque or vehicle speed. We applied the Taguchi method to this development and succeeded in selecting the optimum combination of component levels in the system.

Reduction in the cycle-to-cycle variation (CCV) of combustion in internal combustion engines is required to reduce fuel consumption, exhaust emissions, and improve drivability. CCV increases at low load operations and lean/dilute burn conditions. Specifically, the factors that cause CCV of combustion are the cyclic variations of in-cylinder flow, in-cylinder distributions of fuel concentration, temperature and residual gas, and ignition energy. However, it is difficult to measure and analyze these factors in a production engine. This study used an optically accessible single-cylinder engine in which combustion and optical measurements were performed for 45 consecutive cycles. CCVs of the combustion and in-cylinder phenomena were investigated for the same cycle. Using this optically accessible engine, the volume inside the combustion chamber, including the pent-roof region can be observed through a quartz cylinder.

Cycle-to-cycle variation (CCV) of combustion in low load operation is a factor that may cause various problems in engine operation. Variable valve timing and variable ignition timing are commonly used as a means to reduce this variation. However, due to mountability and cost constraints, these methods are not feasible for use in motorcycle engines. Therefore, development of an engine with minimal CCV without utilizing complicated mechanisms or electronic control is required. CCV of combustion may be caused by fluctuations in in-cylinder flow, air-fuel mixture, temperature, residual gas and ignition energy. In this study, the relationship between CCV of combustion, in-cylinder flow fluctuation and air-fuel mixture fluctuation was the primary focus. In order to evaluate in-cylinder flow fluctuation, Time Resolved Particle Image Velocimetry (TR-PIV) technique was utilized.

Recently it is becoming more necessary than ever to carry out performance prediction and factor analysis at the initial design by-computer aided engineering (CAE), in order to ensure the high performance, safety and reliability of motorcycles and also to shorten the lead time of product development. Finite element method (FEM) plays a crucial role in this respect. In particular, since the vibration characteristic is one of the most important evaluation items, the demand for accurate vibration prediction at the initial design has become much more intense. In recent years, vibration simulation methods have achieved remarkable progress, and especially the substructural synthesis method (SSM), combined with FEM, is used as an effective tool for the requirements.

In order to obtain more reduction of two-stroke motorcycle engine noise than usual, it becomes necessary to make improvements within the combustion process itself. This study was carried out for two objectives. One is the investigation of the relationship between combustion and noise, and the other one is the development of noise reduction techniques. As the result, it was discovered that there was a significant correlation between engine noise and (dP/dθ)max, called the maximum rate of cylinder pressure rise. Therefore, the reduction of the (dP/dθ) max was recognized to be effective for engine noise reduction. The optimized alteration of combustion chamber shape is the most effective noise reduction technique, because it is able to reduce (dP/dθ) max without any sacrifice of engine power. In fact, the level of noise reduction can be predicted by one of the parameters obtained from the combustion chamber shape.

Yamaha Motor Co., Ltd. has been developing 1kW generator system of direct methanol fuel cell (DMFC). The performance and durability characterization of a 1kW DMFC stack that the weight of the stack was decreased 20% in comparison with that of previous stack was evaluated. The DMFC operation condition was optimized from the design of experiment and the results of the net output. The overall system efficiency of the Yamaha DMFC system using the stack became a maximum in current 20A, was 30%. The stack was generated at 20A under the Daily Start up and Shutdown (DSS) condition for 1500h. This report describes some latest results concerning the durability characterization, which were obtained in the NEDO's project.

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.

YAMAHA MOTOR CO., LTD. has developed the YCLS system described in this report. The YCLS provides electrical support for a mechanical oil pump to offset its disadvantage. This system can reduce oil consumption at low engine speeds. As a result, it achieves its aim of reducing exhaust smoke, thus improving the dirty image of 2-stroke gasoline engines. Since the system reduces oil consumption in actual operation, it can be said that the technology contributes to resource saving.

The in-cylinder flow, mixture distribution, combustion and exhaust emissions in a research, five-valve purpose-built gasoline engine are discussed on the basis of measurements obtained using laser Doppler velocimetry (LDV), fast spark-plug hydrocarbon sampling, flame imaging and NOx/HC emissions using fast chemiluminescent and flame ionisation detectors/analysers. These measurements have been complemented by steady flow testing of various cylinder head configurations, involving single- and three-valve operation, in terms of flow capacity and in-cylinder tumble strength.

This paper reports visualization of behavior of spray, wall film, and initial flame propagation in an SI engine with port fuel injection system for motorcycle in order to directly investigate their influences on combustion and relations among them. Borescopes were used to visualize the flame propagation in the combustion chamber and wall film in the intake port. Various injection systems and injection parameters were tested: injection direction, timing, and size of droplets to investigate the effect of mixture formation. It is concluded that combustion stability under low load condition is greatly influenced by mixture inhomogeneity in the combustion chamber whose evidence is the luminous emission. It is caused by direct induction of considerable amount of liquid fuel with large size of droplets into combustion chamber or too inhomogeneous mixture in the intake port.

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 an experimental method to predict the rolling contact fatigue life of a crankpin in a market vehicle engine. The fatigue life up to pitting was evaluated by two laboratory tests including a fatigue life measurement using a ball-on-disk test machine and a crankpin durability measurement by an engine bench test. The surface observation after the tests revealed that the surface dent triggers pitting in both tests. The Weibull plot of the percent failure vs. cycle to failure as a function of the contact stress was presented. In order to directly evaluate the effect of the contact stress on the lifetime, the lifetime values measured at L50 are plotted in the diagram showing the contact stress vs. cycle to failure. The obtained relation can predict the lifetime under the controlled condition in which the number of maximum torque points is countable.

Motorcycles have been widely used as private transportation means, but are now confronted with difficult situations to meet increasingly stringent noise control regulations which requires various noise abatement technologies. Manufacturers, on the other hand, are required to produce totally balanced motorcycles overcoming restrictions in space, weight, etc. To cope with this situation, utilization of high techniques for measurement and analysis of noise is indispensable including those for detection of noise sources in order to take effective noise abatement measures. Well balanced motorcycles must be protected from tampering or improper maintenance, and it is essential that noise control regulations must be technologically feasible in view of the situation in each country.

A centralized control system utilizing optical communication has been developed. Except for the ignition system, almost all electrical functions are under the centralized control. As a method of simplifying wire harness, the time division multiplex communication system using optical communication is adopted. As a result, this new system has made it possible to reduce the number of wires in wire harness from 174 to 123, that of connectors from 60 to 50, and the weight of the wire harness from 1,600 g to 1,350 g. In addition, this system has allowed to reduce the control units (relays) from 11 to 2 (excluding the ignition system).

Recently, our research has focused on the weave mode. This is a representative vibration mode of motorcycles and is important when considering maneuverability and stability. In a method of analyzing the weave mode, a disturbance is applied to the handle bars of the motorcycle during running and then the response waveform of the roll angle and other items at that time is used to perform estimations. However, when the motorcycle is driven at low speeds, the steering operations of the rider have a large effect on the running data and this makes estimation difficult. Therefore, it was assumed that weave mode data can be estimated from slalom running data since this possesses almost the same vibration frequency as the weave mode in low speed range. In this research, a simulation was used to investigate the relationship between the weave mode and slalom running.

Combustion phenomena inside the actual Gasoline-Direct-Injection (GDI) engines have been drawing high attention to its emission characteristics as well as its potential to deal with ultra lean mixture. Although the detailed observation is necessary for its improvement, combustion visualization seems to be strangely overlooked for some reason. This study focuses on the direct observation of GDI combustion to clarify the difficulties behind GDI concept by using a test engine of an actual “wall-guided” configuration and by comparing GDI spray quality with diesel spray in a high-pressure constant volume bomb. The results show that some of the problems about GDI combustion seem to be rather essential than easily conquered, which suggests the necessity for another combustion concept.