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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.

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.

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.

This paper proposes a novel engine starter system composed of a small-power electric motor and a simple mechanical valve train. The system makes it possible to design more efficient starters than conventional systems, and it is especially effective to restart engines equipped with idling stop systems. Recently, several idling stop systems, having intelligent start-up functions and highly-efficient generate capabilities have been proposed for motorcycles. One of challenges of the idling stop systems is the downsizing of electric motors for starting-up. However, there are many limitations to downsize the electric motors in the conventional idling stop systems, since the systems utilize the forward-rotational torque of the electric motors to compress the air-fuel mixture gas in the cylinders. Our studies exceeded the limitations of downsizing the electric motors by mainly using the engine combustion energy instead of the electric energy to go over the first compression top dead center.

A construction of the technology concerning fuel consumption improvement is an important problem not only for the four-wheeled vehicle but also for the motorcycle in recent years when petroleum resources are depleted rapidly. Yamaha originally developed a new fuel injection system (YMJET-FI) and applied the system to a single cylinder, water-cooled and small-displacement engine. In this paper, we would introduce the results of improving the fuel economy with keeping high performance. Improvements were noted in three matters, namely, in the lower load range, 1.Strengthening of in-cylinder flow, 2.Atomization of fuel spray, and 3.Reduction of wall film quantity.

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.

With the hope of efficient and sophisticated motorcycle engine development, an engine test bed that can simulate vehicle running conditions using an ultra-low inertia motor and high response load control system was constructed, and was applied to the development of engines. By combining an exhaust gas analyzer, an exhaust gas constant volume sampler (CVS), and a data processing system, mass emissions could be measured in various test cycles. This system's advantages for data repeatability and test efficiency compared with a chassis test using a vehicle were confirmed. An acceleration test was conducted to assess running performance, and good agreement with actual driving values was confirmed. In addition, by measuring and evaluating engine response to throttle manipulation, it was possible to evaluate driveability on the test bed. These test findings indicate that this test bed can simulate vehicle driving tests with the engine only and will be a useful tool in engine development.

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.

By orthogonalizing the primary inertia moment vector produced by an engine with many engine vectors, a new engine mounting method called “the orthogonal engine mount system” was designed. This paper explains its theoretical background. In addition, a motorcycle with a two-cylinder engine incorporating this system was analyzed by means of modal analysis and building block approach techniques to determine the effectiveness of the orthogonal engine mount system.

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.

The purpose of this paper is to investigate the effect of the piston shape and weight on the friction losses. The motoring test was conducted on pistons with various shapes, rigidities, and weights at 3000-16000 rpm. The test results suggested that the piston friction loss would be abruptly increased mainly because of the increase in the skirt friction caused by the change of the piston attitude. Then, the piston behavioral simulation was conducted using a two-dimensional rigid model in consideration of the skirt rigidity, which proved the above suggestion. This paper consists of the paper presented at 1990 JSAE Autumn Convention and the results of the investigation we conducted based on the calculation of piston behavioral simulation.

MotoGP is the pinnacle of motorcycle racing, with the world's top riders racing 800cc prototype machines at leading venues around the world. The riders compete against each other to win the title and show their superiority. The manufacturers have improved the engines every year to gain high power with low-fuel consumption. The percentage of the duration in fully open throttle is less than 20% of the race, but the partial throttle is used as much as 80%. Moreover, when the rider accelerates the machine, the front tire is easy to be lifted from the ground. In the middle of corner, the rider cannot open the throttle fully because of the tire slip. Therefore, it is the most important factor to appropriately control a throttle in the partial area. The Drive-By-Wire (DBW) system is one of the solutions for the force control. The vehicle simulation in the engine dyno test helped efficiently to evaluate the DBW.

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).

This study deals with reduced-order modeling of intake air dynamics in single-cylinder four-stroke naturally-aspirated spark-ignited engines without surge tanks. It provides an approximate calculation method for embedded micro computers to estimate intake manifold pressures in real time. The calculation method is also applicable to multi-cylinder engines with individual throttle bodies since the engines can be equated with parallelization of the single-cylinder engines. In this paper, we illustrate the intake air dynamics, describe a method to estimate the intake manifold pressures, and show experimental results of the method.

A periodic impulsive sound at idle is occasionally described as ‘disagreeable’ in two-stroke engines. The relation between combustion conditions, piston vibrations, and the disagreeable sound is analyzed to clarify the phenomena. Some means to alleviate disagreeable sound are then proposed through stabilized combustion, high rigidity sound transfer systems, and refined skirt profiles. Experimental results are shown for the effects on main three factors evaluating disagreeable sound-loudness, impulsiveness, and frequency characteristics. In addition, piston behavior is measured, and the relation between piston motion and disagreeable sound is discussed in this paper.

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.

The two-stroke engines were in the main stream of the outboard motors, but they have been replaced with the four-stroke counterparts reflecting the environmental protection movement in recent years. However, the replacement with four-stroke engines involves increased number of components and additional displacement, and the outboard motors tend to be larger and heavier. This represents an issue, since the maneuverability of the boat is degraded due to the inappropriate weight distribution on the boat. Yamaha outboard motors F300B and VF250A, of which the production started in the year 2009, are equipped with four-stroke engines, and yet achieved the light weight equivalent to their two-stroke counterparts. The production volume of these models reached 20,000 units.

The Bonded Valve Seat System is the latest technology to realize drastic reduction in valve temperature in SI engines characterized by the good thermal conductivity of extremely thin valve seats bonded directly on the aluminum cylinder head. A unique and highly rationalized resistance bonding technique was developed to maintain adequate bonding strength and positioning precision in a short bonding period of around one second. Engineering data on optimization of bonding-section geometry, valve seat material and the surface treatment and bonding parameters were presented and discussed regarding the mechanism. The geometry of the bonding section of the cylinder head was optimized by FEM analysis so that the aluminum material should deform to embed the valve seat ring with the action of expelling the surface contamination and the oxide film. The bonding facility was modified so that the electrode axis should move flexibly according to distortion of the cylinder head during bonding.

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.