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On a bluff body which has a slant surface on the rear upper part, it is well known that the drastic change of a wake structure behind the rear body occurs at 30°of the slant angle. Originally, this critical phenomenon was pointed out by L.J. Janssen, W.H. Hucho, and H.J. Emmelmann in the middle of the 1970s. In 1984, S.R. Ahmed conducted systematic measurements by changing the rear slant angle of the bluff body, called the “Ahmed Body”, to find the critical phenomenon. In the 2000s, D.B. Sims-Williams found that the Ahmed Body had vortex structures which had specific frequencies. However, the relationship between the critical phenomenon and the unsteady behaviour has not been clarified yet. Therefore, as the first step of this study, we measured the unsteady wake behaviour for various slant angles to find the relationship between the Strouhal number and the angle. The characteristics of the fluctuation were captured with two hot-wires.

An air-dam spoiler is commonly used to reduce aerodynamic drag in production vehicles. However, it inexplicably tends to show different performances between wind tunnel and coast-down tests. Neither the reason nor the mechanism has been clarified. We previously reported that an air-dam spoiler contributed to a change in the wake structure behind a vehicle. In this study, to clarify the mechanism, we investigated the coefficient of aerodynamic drag CD reduction effect, wake structure, and underflow under different boundary layer conditions by conducting wind tunnel tests with a rolling road system and constant speed on-road tests. We found that the air-dam spoiler changed the wake structure by deceleration of the underflow under stationary floor conditions. Accordingly, the base pressure was recovered by approximately 30% and, the CD value reduction effect was approximately 10%.

A simulation framework for vehicle aerodynamics using up to 10 billion fully unstructured cells has been developed on a world-fastest class supercomputer, called the K computer, in Kobe, Japan. The simulation software FrontFlow/red-Aero was fully optimized on the K computer to utilize up to 10,000 processors with tens of thousands of cores. A hybrid parallelization method using MPI among processors and OpenMP among cores inside each processor was adopted. The code was specially tuned for unsteady aerodynamic simulation including large-eddy simulation, and low Mach number approximation was adopted to avoid excessive iterations usually required for the fully incompressible algorithm. The automated mesh refining system was developed to generate unstructured meshes of up to 10 billion cells. In the system, users only generate unstructured meshes in the order of tens of millions of cells directly using commercial preprocessing software.

The critical change in drag occurring on the Ahmed body when the slanted base has an angle of 30° is due to a transition in the wake structure. In a previous study on flow analysis across the Ahmed body, we investigated the unsteady wake experimentally using hot-wire and particle image velocimetry measurements. However, because the experimental analysis yielded limited data, the spatially unsteady wake behaviour, interaction between the trailing vortex and transverse vortices (up/downwash), and flow mechanism near the body were not discussed sufficiently. In this study, the unsteady wake structures were analysed computationally using computational fluid dynamics to understand these issues, and the hypothesis was tested. The slant angle was 27.5°, which is identical to that in the experiment and corresponds to a high drag condition indicated experimentally.

A wall-resolving Large Eddy Simulation (LES) has been performed by using up to 40 billion grids with a minimum grid resolution of 0.1 mm for predicting the exterior hydrodynamic pressure fluctuations in the turbulent boundary layers of a test car with simplified geometry. At several sampling points on the car surface, which included a point on the side window, the door panel, and the front fender panel, the computed hydrodynamic pressure fluctuations were compared with those measured by microphones installed on the surface of the car in a wind tunnel, and effects of the grid resolution on the accuracy of the predicted frequency spectra were discussed. The power spectra of the pressure fluctuations computed with 5 billion grid LES agreed reasonably well with those measured in the wind tunnel up to around 2 kHz although they had some discrepancy with the measured ones in the low and middle frequencies.

In open-grille vehicle aerodynamics simulation using computational fluid dynamics, in addition to basic flow characteristics, such as turbulent flow with a Reynolds number of several million on the bluff body, it is important to accurately estimate the cooling air flow introduced from the front opening. It is therefore necessary to reproduce the detailed geometry of the entire vehicle including the engine bay as precisely as possible. However, there is a problem of generating a good-quality calculation grid with a small workload. It usually takes several days to a week for the pretreatment process to make the geometry data ‘clean’ or ‘watertight’. The authors proposed a computational method for complex geometries with a hierarchical Cartesian grid and a topology-independent immersed boundary method with dummy cells that discretize the geometry on a cell-by-cell basis and can set an imaginary point arbitrarily.

The purpose of this study is to show cycle-to-cycle combustion variation in transient conditions of quick throttle opening and to control the combustion fluctuation improve acceleration in a two-stroke motorcycle engine. Two phases of engine operation were focused on: the low-load condition before quick throttle opening, and the transient condition after quick throttle opening. The time-series variation of the heat release rate based on the in-cylinder pressure, the engine-speed and the exhaust pressure variation were measured simultaneously, in an engine with a new multiple-timing-ignition-system, and in an engine with a modified exhaust port. Stable ignition performance and fast burning velocity were the keys to attaining smooth acceleration.

The purpose of this study was to find compatible specifications both of emission reduction and high power output with good throttle response for a sports utility motorcycle. In the emission reduction challenge, we examined equipping the exhaust system with a catalytic converter to achieve sufficient emission reduction. The catalytic converter, however, caused a temperature rise in the exhaust system, which caused a pressure propagation change. Additional muffler design optimization effectively maintained high performance and acceleration. The exhaust valve device was also optimized for emission reduction and high power output over a wide engine speed range. The optimized control of the exhaust valve was beneficial to preventing short-circuit of fresh mixture gas and early activation of the catalyst. Such comprehensive specifications could satisfy the performance and driveability characteristics required for sports utility motorcycles.

The Emission Regulations for Motorcycles in Japan was put into effect in October 1998 with the goal of reducing the total hydrocarbon emissions from motorcycles in the country to around 50% of the present amount. These regulations initiated a need to develop emission-converting catalysts, having the three characteristics written below, for two-stroke engines that historically have produced more hydrocarbons than four-stroke engines: 1 High performance of hydrocarbon conversion 2 High light-off performance 3 High thermal stability under high temperature Among a number of catalytic adjustment methods, the loading method of precious metals and the washcoat preparing method were modified to realize mass production of high-performance, low-cost catalysts.

When the planing craft with outboard motor is running, cavitation occurs around the surface of propeller and lower unit of outboard motor. Cavitation has been classified under several categories by the feature and cause of occurrence. Among them, cloud cavitation and root cavitation lead to erosion damage on the surface of lower unit and propeller. To prevent from poor appearance or performance deterioration of outboard motor by erosion damage, it is important problem to predict the erosion occurrence. Currently we can predict the cavitation phenomena sufficiently, but the area of cavitation does not necessarily correspond with the area of erosion. In this study, we present the new method to predict the area of erosion due to cavitation using CFD (computer fluid dynamics) analysis. In order to evaluate the accuracy of erosion occurrence simulation, the simulation results are compared against the result of a full-scale cruising test.

This paper describes our attempts to improve the power generation efficiency of single-phase permanent magnet generators of outer-rotor type for motorcycles by their reducing electric losses (iron loss and copper loss) by electromagnetic analysis. In this study, we first broke down the electric losses into iron loss and copper loss by electromagnetic analysis. Then, focusing on the iron loss that the loss ratio was high, we modified the thickness and material of the stator core sheets and reduced the iron loss in the non-magnetic protection covers of the magnets on the rotor, and thus improved power generation efficiency. Further, we analyzed the flow of magnetic flux and magnetic flux density and found that it would be effective against leakage of the flux between the magnets if we spaced the magnets, which we did and which also allowed us to reduce the amount of magnets used.

It has become clear that a motorcycle rider regards the sound and vibration which occurs from a motorcycle as a feeling of a “Kodo-kan” which is not unpleasant and becomes a part of comfortable nature. In this paper, the physical quantity relevant to a feeling of a beat was extracted from the sound and oscillating measurement data of an idling state for the purpose of quantification of the feeling evaluation of a “Kodo-kan” of the motorcycle, and the feeling evaluation score prediction of a beat was tried from the physical quantity.

In this study, to improve the cruising performance of planing craft with outboard motor, we have examined a estimation method of the hull attitude angle at cruising and resistance in case of changing the tilt angle and mounting position of the outboard motor by the tank test using a scale model of a hull and an outboard motor in the ship testing tank. Planing craft with outboard motor have different characteristics from large vessels. The characteristics are shown below. The hull attitude angle at cruising is different in each forward speed. The thrust accounted for a large percentage of hull weight. And the flow field around the hull changes along with the operation of the propeller. The hull attitude angle at cruising is changed by the rigging state of the outboard motor.

The electrodeposition painting can make a coat adhere not only to the exterior surface but also on the inside of an object, and has excellent corrosion resistance. Therefore, it is widely used as paint for anti-corrosion to various vehicles. In electrodeposition painting, by the electricity from an electrode flowing into the surface of an object through paint solution, a paint deposits to the surface of an object and a paint film is formed. Therefore, if the object is simply in contact with paint solution, a paint film will not necessarily be formed. For example, even if paint solution has touched, since the electrical resistance of paint solution is not high, sufficient current flows through the outside of a motorcycle frame, nor the inner surface of the automobile body and a paint film may not be formed. In order to check the paint film thickness of electrodeposition painting conventionally, it was measuring by disassembling the actually painted object.

The Mechanical CVT is mainly used for small size motorcycle called “scooter”, which has a 250 cc or less engine capacity. The speed characteristics of the Mechanical CVT are decided by engine speed and load-torque on driven pulley. In few papers, these characteristics are studied under full-load or no-load condition [1]-[2]. However, the characteristics at part-load condition are not well known. To develop a motorcycle with low fuel consumption, it is important that the characteristics at part-load condition are considered in driving cycle. Driving cycle simulation is needed to estimate CVT ratio at design stage. This research proposes equations representing the speed characteristics of the Mechanical CVT at part-load condition. Driving cycle simulation is also developed for estimation of the fuel consumption at optional driving cycles and the dynamic behavior of the CVT system. It could be a CVT design tool to makes sure whether its performance is achieved for design targets.

Traditionally, a Boundary Element Method (BEM) is often used for a radiation noise analysis. In recent years, to define an infinite region, a Finite Element Method (FEM) that can use an infinite boundary condition has been developed. However, studies on the radiation noise analysis by the FEM are few. Recently a number of an electric scooter has been increased. One of development issues is a radiation noise by a vibration of a wall surface of a swing-arm. In this paper, the vibration of the wall surface of the swing-arm is calculated, and a sound pressure level (SPL) of the radiation noise is calculated using a result of the frequency response analysis. And compare results of an experimental and an analytical sound pressure, its results were matched to within 5% error. Furthermore we used the method of this paper, proposed the model to reduce the radiation noise 10dB. Then we compare with the FEM and the BEM to verify the computation time and the mesh size.

Anodizing is applied to improve the durability and the corrosion resistance of aluminum alloy parts of engines and car bodies. Generally, anodic oxide film is formed using direct current anodizing (DCA). However, in the case of anodizing high silicon aluminum alloy cast parts, it is difficult to derive uniform film thickness distribution. Furthermore, it takes a long treatment time which causes low productivity. In this study, the authors have developed an anodizing method by using high-frequency switching anodizing (HSA) to solve these problems. The growth process of anodic oxide film is susceptible to the metallographic structure. Thus, the typical DCA application to the high silicon aluminum alloy produces a non-uniform film thickness, while HSA has the potential to form uniform film without being affected by metallographic structure. Moreover, the current density of HSA is higher than that of DCA which reduces treatment time to 1/5 as the film formation enhances.

Suzuki Motor Corporation unveiled the Burgman Fuel Cell Scooter (Burgman FCS) at the “TOKYO MOTOR SHOW 2009”. It is a simple and high-efficiency fuel cell scooter, which is equipped with a compact and unique air-cooled fuel cell system, jointly developed with the UK firm, Intelligent Energy Ltd. In order to evaluate the vehicle performance and find any powertrain related issues from actual road and traffic conditions, it has been tested in a fleet testing program supported by the UK Technology Strategy Board (TSB), in UK since February 2010. In addition, seeking for different operating conditions, it is planned to provide it in 2011 to a further field test to be held in Japan. Additionally in March 2011, it obtained Whole Vehicle Type Approval (WVTA) in the European Union; the first time this has been achieved for any fuel cell vehicle. This proved that it has achieved the high level environmental acceptability and safety requirements which are essential for the practical scooter.

Lead-added free-cutting steel has been used by many parts which need high machinability because lead improves chip friability and drill life. However, the demand of lead reduction increases in recent years, because of environmental impact substance reduction. Therefore, we developed lead-free crankshaft for motorcycle. Until now, crankshaft for motorcycle has been manufactured with lead-added free-cutting steel by a following process; Hot-Forging - Quenching and Tempering (QT) - Prior Machining - Nitrocarburizing - Finishing process because of strength and machinability. When we tried to change steel to lead-free, we examined to change to sulfur-added free-cutting steel. However, chip friability of sulfur-added free-cutting steel is inferior to lead one. Thus, we concerned about increase in machining expense. Then, heat-treatment after forging was examined to change from QT to normalizing for reducing the heat-treatment expense.

Gear shift feeling is often an important factor which appeals to motorcycle riders. Therefore, it is important for designers to create a pleasant gear shift feeling when developing a motorcycle. Sensory evaluation tests are indispensable for quantifying the gear shift feeling, but are very difficult to conduct with an actual motorcycle. Therefore, we developed a simulator dedicated to sensory evaluation tests, used it to conduct sensory evaluation tests, and thus clarified the relationship between the physical amount of gear shift properties and gear shift feeling. This paper describes the development of the simulator, the sensory evaluation tests conducted on gear shift feeling using the simulator, and the results of analysis.