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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.

Various sensors including throttle position sensors (TPS), manifold pressure sensors (MPS), crank angle sensors, engine temperature sensors, and oxygen sensors are mounted in electronically controlled fuel injection (FI) systems to accurately regulate the air-fuel ratio according to the operating state and operating environment. Among these vehicle-mounted sensors, TPS has functions for detecting a fully-closed throttle and estimating intake air volume by the amount of throttle opening. Currently, we have conducted a study on transferring TPS functions into the MPS (manifold pressure sensor) in order to eliminate the TPS. Here we report on detecting a fully-closed throttle for achieving fuel cut control (FCC) and idle speed control (ISC) in fuel injection systems. We contrived a means for fully-closed throttle detection during ISC and controlling changes in the bypass opening during FCC in order to accurately judge each fully-closed throttle state via the manifold pressure.

Cost reduction is an important development goal for small motorcycles (1). As a way to reduce costs, we have developed an electronically controlled fuel injection (hereafter FI) system without a throttle position sensor (hereafter TPS). Ordinarily, the high throttle range is controlled and computed by TPS, and the low throttle range by manifold pressure sensor (hereafter MPS). The intake airflow is estimated with consistent high precision regardless of the engine load, and the basic fuel injection is executed accordingly. Also, transient correction monitors the size of TPS changes, to inject fuel immediately when a TPS change equal to or greater than a threshold value is detected. In our development, we replaced these functions with control by MPS. For calculation of basic fuel injection quantity by MPS, we carried on the conventional method. However, MPS transient correction control had some aspects with poor tracking.

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 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.

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.

We have developed an electronically controlled four-speed automatic transmission with a "D-range neutral control system" for vehicles of small piston displacements (0.66 to 1.0 liter). When the vehicle is stationary with the engine idling, the system reduces the pressure being supplied to the clutch, thereby creating a neutral clutch condition. This helps reduces fuel consumption of the stationary vehicle without intervention of the driver. The non-intervention, however, can cause discomfort for the driver when the system is engaged and disengaged as the vehicle condition (i.e., engine revolution speed, vibration or noise transmitted to the vehicle) may change noticeably. Such a cause of discomfort that surfaced during the system development stage was thoroughly investigated and successfully eliminated by improving the method of control.

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 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.