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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.

Recently the response of the engine speed at starting has more importance than ever for quick start satisfying rider’s needs, as well as exhaust emissions. We have developed a simulation for studying engine and starter specifications, engine control algorithm and other engine control parameters. This system can be utilized to realize appropriate starting time by considering air-fuel ratio under various conditions. This paper addresses what are taken account of in our method. Examples applying this to a conventional motorcycle engine are shown.

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.

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.

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.

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.

This paper concerns a torque control of a rear wheel of a motorcycle equipped with a rubber/aramid belt electronically-controlled continuous variable transmission where a primary sheave position is controlled by an electric motor. In particular, the paper discusses a method to calculate a required engine torque and a required primary sheave position, given reference values of a rear-wheel torque and an engine rotational velocity. The method forms a foundation of a hierarchized traction control where a higher control layer decides an optimal motorcycle motion (rear-wheel torque and engine rotational velocity) and a lower control layer realizes the motion by actuators (engine torque and primary sheave position). Difficulties of the control are due to large mechanical compliance of the rubber/aramid belt, which leads to an inevitable lag from the primary sheave position to a speed reduction ratio.

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.

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.

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.

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.

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.

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.

This paper presents a practical simulation model of the rubber V-belt CVT which is widely used as a low cost driveline element for small displacement motorcycles. The characteristic of this CVT is determined by the axial force balance between driver and driven pulleys, and the elastic force of a rubber V-belt. Because these axial and elastic forces are calculated by the kinematic and FEM analysis, a large-scale simulation model which costs long execution time for the calculation is needed to estimate the characteristic of CVT. This calculation uses the one-dimensional simulation model built up with MATLAB and SIMULINK environment, so that it was possible to get the calculation result with relatively low execution time. The elastic deformation of the rubber V-Belt was calculated by a simple spring model which was verified by experiments and FEM.

The continuously variable transmission (CVT) with a rubber belt used in scooters is also regarded as a potential automatic transmission mechanism for conventional motorcycles. By making this system more compact and building it into the engine, a motorcycle CVT engine has been developed that is about the same size as a manual transmission (MT) engine. During driving with a CVT, heat is generated by friction at the sheaves, and therefore it was necessary to secure a certain length of belt to ensure that external air flows efficiently to the sheaves. However, making the CVT more compact restricted the belt length, which decreased cooling performance and increased the number of bends in the belt, making it difficult to maintain durability. To address this issue, a plastic resin drive belt and newly designed sheaves were adopted, and durability of more than that of a scooter was achieved.

Mixture formation is one of the most important factors for the combustion in the spark ignition engine with port fuel injection. The relation between combustion and mixture quality, however, is not quantitatively well established. In this study, the connection of combustion and mixture formation was explored with various measurement techniques. Borescopes were used in order to investigate the flame propagation in the combustion chamber and behavior of spray and fuel film on the wall in the intake port. For the purpose of investigation on the effect of mixture formation, various port fuel injection systems and parameters were tested and compared: direction, timing, and size of droplet. An SI engine for small vehicle was used under condition of 4 000 rpm. The investigation by images obtained has shown that inhomogeneity of mixture causes low combustion stability, especially due to direct introduction of fuel droplets into the combustion chamber.

Yamaha Motor Co., Ltd. has developed the new model EC-03 designed and engineered with technology developed under the Company's Smart Power ideal. Launched on the market in September 2010, the Model is an “electric commuter” entry in the personal mobility category that is expected to show increasing demand in the future.

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.

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.

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.