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The improvement of fuel consumption is the most important issue for engine manufactures from the viewpoint of energy and environment conservation. A piston-cylinder system plays an important role for the reduction of an engine friction. For the improvement of the frictional behavior of the piston-cylinder system, it is beneficial to observe and analyze the frictional waveforms during an engine operation. To meet the above-mentioned demand, frictional waveforms were measured with using the renewed floating liner device. In the newly developed floating liner device, an actual cylinder block itself was used as a test specimen. The measured single cylinder was an aluminum monolithic type made of hypereutectic Al-17%Si alloy using a high pressure die casting process. The combined piston was a light weight forged piston and a DLC coated piston ring was used. For the measurement, 110cc air cooled single cylinder engine was used.

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.

Gasoline fueled Homogeneous Charge Compression Ignition (HCCI) combustion with internal exhaust gas re-circulation using Negative Valve Overlap (NOL) was investigated by means of calculation and experiment in order to apply this technology to practical use with sufficient operating range and with acceptable emission and fuel consumption. In this paper we discuss the basic characteristics of NOL-HCCI with emphasis on the influence of intake valve timing on load range, residual gas fraction and induction air flow rate. Emission and fuel consumption under various operation conditions are also discussed. A water-cooled 250cc single cylinder engine with a direct injection system was used for this study. Three sets of valve timing were selected to investigate the effect of intake valve opening duration. Experimental results demonstrated that an engine speed of approximately 2000rpm yields an NMEP (Net Mean Effective Pressure) range from 200kPa to 400kPa.

In this study, lean combustion concept was investigated to realize better Fuel Economy (FE) on a single cylinder motorcycle engine. A low-pressure direct injection (DI) system was applied to realize lean stratified combustion concept with good combustion stability. In addition, Exhaust Gas Recirculation (EGR) system applicable to small motorcycle engines was used to attain FE improvement and NOx reduction. EGR gas temperature and EGR return position were focused on and effects on FE and NOx were investigated. Computational Fluid Dynamics (CFD) was used to reveal EGR distribution and air motion in both the intake port and the cylinder. As a result, the influence of the stratified charge, EGR temperature and EGR return position on FE and NOx were explained quantitatively. These techniques were effective in reducing NOx and improving FE for a single cylinder motorcycle engine.

Attempts have been made to develop an electronically controlled fuel injection system that is ideal for small motorcycles, cost-efficient, compact, and electric power-saving while maintaining accuracy. For reducing the number of sensors and cost, highly accurate methods have been developed for the measurement of intake air mass, detection of acceleration, distinction of engine stroke, and estimation of atmospheric pressure without using a throttle position sensor, cam timing sensor, and barometric sensor in such a manner as to carry out sampling with the intake manifold pressure of single-cylinder engines synchronizing with the crank angle. For compactness and electric power saving, an injector and in-tank fuel pump module have been developed for small motorcycles.

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.

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.

We compared motoring friction loss, output performance at WOT (wide open throttle) and specific fuel consumption of big-end bearings on engines having identical specifications between the case of using plain bearings and rolling bearings to investigate the effect of the lubricating oil supply rate on these parameters in an attempt to improve output through reduction of friction loss for big-end bearings of small, high-output motorcycle engines. Testing was performed using a 125 cc, 4-cycle, single cylinder engine at high engine speeds mainly above 10,000 rpm.

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.

Any improvements of the fuel economy with engines are always required for all petroleum fuel vehicles. The goal of such improvements must lead to reduce fuel consumption of the engines. However it may cause some deterioration with riding feeling that is one of the most important characteristics of the motorcycles. Yamaha has developed the strong hybrid motorcycle "HV-X"(hereafter the motorcycle). The motorcycle consists of a 4-stroke 250 cm₃ a cylinder engine and two 300V AC motors with a planetary gear set. The motorcycle reduces fuel consumption without severe influence onto the drive performance by utilizing the electric power.

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.

This paper describes aspects of YAMAHA 2 cycle, high speed, high output engines. Generally speaking, in order to obtain good results in developing engine performance, high delivery ratios and high thermal and mechanical efficiencies are essential. In addition to these, the most suitable cooling and lubricating systems must be employed. YAMAHA has developed a separate and automatic lubrication system for 2-cycle gasoline engines, which keeps YAMAHA engines well lubricated.

In this study, an improvement of fuel consumption by changing the exhaust timing of a two-stroke engine has been made. The study results revealed that a remarkable improvement of fuel economy is possible by controlling the exhaust timing according to the engine speed. The reason for the better fuel economy was clarified through an analysis of exhaust gases, theoretical cycle calculations, and an analysis of combustion pressure. As an example of actual application, the results of tests made on an engine equipped with Yamaha power Valve System (YPVS), which is a variable exhaust timing mechanism using a tabor-shaped valve, will also be discussed.

It is in the plating process that the worst bottleneck occurs in plant automation. We, however, have succeeded in making our plating process free from pollution and compact, allowing us to install this system within a production line and consequently establish a continuous production line resulting in a decrease in plating cost to about 1/2 of the previous cost. We have achieved an excellent chrome plating speed of 60µ/min, by placing an anode relatively close to the part to be plated and by sending the plating solution into the space between the two by means of a pump. This provides a plating speed 100 times faster than with conventional methods, while improving the quality of the plating coat considerably. The system is optimum for functional platings, and can be used for the plating of shock absorber rods, engine valves, engine cylinders, etc.

THE MULTI-VALVE FOUR STROKE CYCLE engine design trend is Coward increased engine power and higher fuel efficiency. While a four-valve system is the most common direction, problems occur when the valve area is widened by increasing the cylinder bore for a higher engine output. The layout of four larger valves causes the combustion chamber shape to flatten and the combustion time period to increase. In pursuit of the optimum multi-valve engine we have studied four, five, six and seven-valve per cylinder design. Performance targets and design constraints led us toward the successful five-valve engine technology. This technology develops high engine torque and efficient combustion over a wide range of engine speeds.

Carburized and quenched materials with high fatigue strength are often used for motorcycle engine parts. Nitrided materials exhibit less deformation during heat treatment than carburized and quenched materials, so if the same or higher fatigue strength can be achieved with nitrided materials as with carburized and quenched materials, the geometric precision of parts can be increased and we can reduce engine noise as well as power loss. When the fatigue strengths of a nitrided material with its compound layer surface put into γ’ phase through nitriding potential control (hereafter, G), and a nitrided material put into ε phase (hereafter, E) were measured, the results showed the fatigue strength of the G to be about 11% higher than that of carburized and quenched materials. It was inferred that the strength of the compound layer determines fatigue strength.

With emergence of fuel cells which have much better thermal efficiency than internal combustion engines (later abbreviated as ICE), ICE has to improve its thermal efficiency to the level of 50%. One of the ways to improve the thermal efficiency of ICE is to utilize ultra-lean combustion and several technical papers have been published. But it seems the thermal efficiency has not been improved as the theory predicts. The test data of these technical papers were re-examined and it was concluded that the thermal dissociation of burned gas and NOx formation is the key factor of a discrepancy between the theory and the actual test data. In order to prevent an occurrence of thermal dissociation, emulsified fuels (mixture of carbonaceous fuels with water) was proposed.

The specific output of 4-cycle engines are generally smaller than that of 2-cycle engines. Increasing engine speed is one method to improve the specific output, however, it contains some disadvantages in application. Hence, improvement in torque with the 4-cycle engine is desirable. Although torque could be improved by super-charging, it seems difficult to apply existing systems for small displacement engines due to problems of their size and cost. We have, therefore, newly developed a super-charging system named Advanced Crankcase Super Charge (hereinafter referred to as ACSC) using a crankcase as a supercharger. In this study, we made a 50cc single cylinder prototype engine with ACSC and carried out the engine unit tests and actual running tests on a scooter. From these tests, the torque that is twice as that of the naturally aspirated engine was obtained.

In the past, the performance of motorcycle engines has improved quite rapidly through intensive competition in racing and in the marketplace. Motorcycle engines have contributed to the technological progress of internal combustion engines (hereafter abbreviated as ICE). Today's environmental concerns require motorcycle engines to improve fuel economy and exhaust emission pollutants. After examination of potential measures to improve the thermal efficiency of small engines, it was concluded that if engineers of motorcycle engines fail to take on new ideas such as those being developed in cold fusion, it is foreseen that motorcycle engines will be replaced with new power plants as was seen on locomotives in the past.

In recent years, global warming, depletion of fossil fuels, and reducing pollution have become increasingly prominent issues, resulting in demand for environmentally-friendly two-wheeled vehicles capable of reducing CO2 emissions. However, it remains necessary to meet customers’ expectations by providing smaller drivetrains, lighter vehicles, and support for long-distance riding, among other characteristics. In the face of this situation, hybrid electric vehicle (HEV) systems are considered to be the most realistic method for creating environmentally-friendly powertrains and are widely used. This research introduces a hybrid electric two-wheeled vehicle fitted with an electrical variable transmission (EVT) system, a completely new type of electrical transmission that meets the aforementioned needs, achieving enhanced fuel efficiency with a compact drivetrain. The EVT system comprises double rotors installed inside the stator.