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5 belt wind tunnels are the most common facility to conduct the experimental aerodynamics development for production cars. Among aerodynamic properties, usually drag is the most important development target, but lift force and its front/rear balance is also important for vehicle dynamics. Related to the lift measurement, it is known that the “pad correction”, the correction in the lift measurement values for the undesirable aerodynamic force acting on wheel belt surface around the tire contact patch, must be accounted. Due to the pad correction measurement difficulties, it is common to simply subtract a fixed amount of lift values from measured lift force. However, this method is obviously not perfect as the pad corrections are different for differing vehicle body shapes, aerodynamic configurations, tire sizes and shapes.

This research investigated the mechanism of the effects of hydraulic dampers, which are attached to vehicle body structures and are known by experience to suppress vehicle body vibration and enhance ride comfort and steering stability. In investigating the mechanism, we employed quantitative data from riding tests, and analytical data from simplified vibration models. In our assessment of ride comfort in riding tests using vehicles equipped with hydraulic dampers, we confirmed effects reducing body floor vibration in the low-frequency range. We also confirmed vibration reduction in unsprung suspension parts to be a notable mechanical characteristic which merits close attention in all cases. To investigate the mechanism of the vibration reduction effect in unsprung parts, we considered a simplified vibration model, in which the engine and unsprung parts, which are rigid, are linked to the vehicle body, which is an elastic body equipped with hydraulic dampers.

At present, measurements of running resistance are conducted outdoors as a matter of course. Because of this, the ambient temperature at the time of the measurements has a considerable impact on the measurement data. The research discussed in this paper focused on the temperature characteristic of the tires and developed a new correction technique using a special rolling test apparatus. Specifically, using a tire rolling test apparatus that made it possible to vary the ambient temperature, measurements were conducted while varying the levels of factors other than temperature that affect rolling resistance (load, inflation pressure, and speed). Next, a regression analysis was applied to the data for each factor, and coefficients for a relational expression were derived, making it possible to derive a quadratic equation for the tire rolling resistance correction formula.

In motorcycles, the mass difference between a vehicle and a rider is small and motions of a rider impose a great influence on the vehicle behaviors as a consequence. Therefore, dynamic properties of motorcycles should be evaluated not merely dealing with a vehicle but considering with a man-machine system. In the studies of a simulation for vehicle dynamics, various types of rider models have been proposed and it has already been reported that rider motions have a significant influence on the dynamic properties. However, the mechanism of the interaction between a rider and a vehicle has not been clarified yet. In our study, we focused on weave motion and constructed a full vehicle simulation model that can reflect the influences of the movements of the rider’s upper body and lower body. To construct the rider model, we first measured the vibrational characteristics of a human body using a vibration test bench.

In motorcycles traveling at medium to high speed, roll stability is usually maintained by restoration forces generated by a self-steering effect. However, when the vehicle is stationary or traveling in low speed, sufficient restoring force does not occur because some of the forces, such as centrifugal force, become small. In our study, we aimed at prototyping a motorcycle having roll stability when the vehicle is stationary or at low speed with a steering control for self-standing assist, while maintaining stability properties in medium to high speed. A model was built to represent dynamics of roll motion, which is composed of a fixed point mass located above the vehicle’s center of gravity and another movable point mass below that gravity center. According to the model, when steered, the roll moment direction generated by the shift of the movable point mass becomes the same as the direction generated by the ground contact point shift of the front tire.

Designing a lightweight and durable engine is universally important from the standpoints of fuel economy, vehicle dynamics and cost. However, it is challenging to theoretically find an optimal solution which meets both requirements in products such as the cylinder head, to which various thermal loads and mechanical loads are simultaneously applied. In our research, we focused on “non-parametric optimization” and attempted to establish a new design approach derived from the weight reduction of a cylinder head. Our optimization process consists of topology optimization and shape optimization. In the topology optimization process, we explored an optimal structure with the theoretically-highest stiffness in the given design space. This is to provide an efficient structure for pursuing both lightweight and durable characteristics in the subsequent shape optimization process.

When fluctuations in the speed of rotation of the drive pulley are transmitted to the driven pulley via the metal V-belt, the transmitted fluctuations become attenuated as friction force approaches a state of saturation. The research discussed in this paper focused on these fluctuations in the speed of rotation and developed an index for the slip state between the belt and the pulleys. The drive and driven pulleys were regarded as a one-dimensional vibrating system connected by elastic bodies, and changes in the state matrix of the system were focused on. It was determined that when all of the eigenvalues in this state matrix become real numbers, slip speed between the belt and the pulleys increases sharply. A method was proposed of estimating this behavior of the eigenvalues from changes in the speed of rotation of the drive and driven pulleys, and indexing the current slip state.

The change in the aerodynamic lift force (henceforth CL) by heave motion is discussed in this paper in order to clarify the effect of aerodynamic characteristics on the vehicle dynamic performance. We considered that phenomenon in actual car running at 160km/h and 1Hz heave frequency. Using a towing tank to change its water from the air to the working fluid to more easily observe this phenomenon. That makes possible to observe the same phenomenon with reduced velocity and small models under same Strouhal number condition. This method can be reducing vehicle speed to 3m/s (1/15 actual) and frequency to 0.2Hz (1/5 actual) in case using 40% scaled model. The results of these tests showed that unsteady CL is proportional to heave motion. These results showed the proportional relationship between unsteady CL and heave motion. The formularization of unsteady CL made it possible to introduce shape coefficients to vehicle dynamics simulations as functions of heave velocity.

Predicting fuel consumption and performance of an outboard motor for a high speed small planing boat are numerically challenging. The propeller is one of the most popular propulsion systems used for outboard motors. We focused our attention on the fact that the thrust performance of a propeller has a major impact on cruising fuel consumption and performance. We believe that we can numerically predict cruising fuel consumption, which has conventionally been estimated through experiential means, using accurate thrust performance measurements via CFD simulation without cavitations model. This study aims to develop a simulator that could quantitatively predict cruising fuel consumption and performance of an outboard motor used for a high speed small planing boat. After comparing the CFD simulation of propellers against the results of model tests, the simulated results are in good agreement with the experimental results.

The effects of aerodynamic coefficients on handling response and flat ride were quantified. For handling response, the aerodynamic effect was quantified by analysis with linear representation and a two-wheel simulation model, using aerodynamic coefficients obtained from a full scale car wind tunnel. The correlation of aerodynamic coefficients and handling response with driving feel was also ascertained. Aerodynamic yaw moment and side-force were also converted to equivalent front and rear lift to standardize aerodynamic indexes and improve aerodynamic development efficiency. For flat ride, steady and unsteady aerodynamic effects were quantified by analysis with a two-degree-of-freedom mass-spring-damper simulation model and aerodynamic coefficients obtained from a 35% scale model wind tunnel and towing tank test. Unsteady aerodynamic force occurrence mechanism was ascertained by unsteady CFD using dynamic mesh.

Super-sport motorcycles have shorter wheelbases than other category motorcycles. Due to this, strong braking occasionally causes large pitching motions to occur, including rear-wheel-lift. In order to reduce such pitching motions and achieve an effective braking force, the authors have developed a brake-by-wire system that uses a pressure sensor to detect the braking input pressure and an electric actuator to variably control the hydraulic pressure. This system makes it possible to precisely control the braking force compared with the previous ABS. Large pitching control was performed by the distribution of a front wheel and a rear-wheel braking forces, CBS (Combined Brake System), by using electronic control, and Brake-by-Wire has been suitable for sport riding. As a result, stable braking performance could be obtained without spoiling the handling characteristics of super-sport motorcycles.

Determination of an engine's inertial properties is critical during vehicle dynamic analysis and the early stages of engine mounting system design. Traditionally, the inertia tensor can be determined by torsional pendulum method with a reasonable precision, while the center of gravity can be determined by placing it in a stable position on three scales with less accuracy. Other common experimental approaches include the use of frequency response functions. The difficulty of this method is to align the directions of the transducers mounted on various positions on the engine. In this paper, an experimental method to estimate an engine's inertia tensor and center of gravity is presented. The method utilizes the traditional torsional pendulum method, but with additional measurement data. With this method, the inertia tensor and center of gravity are estimated in a least squares sense.

Engine mount loads are mostly measured from load cells or calculated from measured engine accelerations. This paper introduces an innovative new method to calculate engine mount loads from measured spindle loads. The method starts from calculating suspension attachment loads to body or chassis frame, then calculating engine center of gravity accelerations, and finally calculating engine mount loads from engine inertia forces. This spindle-based engine mount load analysis method is validated by a vehicle with measurements by wheel force transducers and engine load cells. The correlation includes load time history, peak-to-peak load range, and pseudo-damage values. The correlations show good comparisons between measured and predicted in all the categories, especially for the high load components. It is recommended to implement this method in early vehicle design phases.

Buffeting is a wind noise of high intensity and low frequency in a moving vehicle when a window or sunroof is open and this noise makes people in the passenger compartment very uncomfortable. In this paper, side window buffeting was simulated for a typical SUV using the commercial CFD software Fluent 6.0. Buffeting frequency and intensity were predicted in the simulations and compared with the corresponding experimental wind tunnel measurement. Furthermore, the effects of several parameters on buffeting frequency and intensity were also studied. These parameters include vehicle speed, yaw angle, sensor location and volume of the passenger compartment. Various configurations of side window opening were considered. The effects of mesh size and air compressibility on buffeting were also evaluated. The simulation results for some baseline configurations match the corresponding experimental data fairly well.

This paper presents a method for optimization design of an engine mounting system subjected to some constraints. The engine center of gravity, the mount stiffness rates, the mount locations and/or their orientations with respect to the vehicle can be chosen as design variables, but some of them are given in advance or have limitations because of the packaging constraints on the mount locations, as well as the individual mount rate ratio limitations imposed by manufacturability. A computer program, called DynaMount, has been developed that identifies the optimum design variables for the engine mounting system, including decoupling mode, natural frequency placement, etc.. The degree of decoupling achieved is quantified by kinetic energy distributions calculated for each of the modes. Several application examples are presented to illustrate the validity of this method and the computer program.

HONDA completed research and development of the Metal V-Belt for CVTs in-house for the purpose of reducing the minimum pitch radius. The newly developed belt is essential to the compactness of a CVT and increases the speed ratio range. Increase of ring stress caused by reducing the minimum pitch radius is treated by improvement of element shape, optimizing clearance between elements and between element and ring and improving materials.(1) In this paper, the optimization of clearance between elements, heat treatment of elements and optimization of ring material are described in detail. Optimum total clearance between elements for a virgin belt is defined by test results during operation using a specially engraved gap sensor and a telemeter system. Tolerance and conditions of heat treatment for elements are optimized concerning fatigue strength of the element nose.

A traction test machine, developed for evaluation of traction-CVT fluids for the automotive consortium, USCAR, provides precision traction measurements to stresses up to 4 GPa. The high stress machine, WAMhs, provides an elliptical contact between AISI 52100 steel roller and disc specimens. Machine stiffness and positioning technology offer precision control of linear slip, sideslip and spin. A USCAR traction test methodology includes entrainment velocities from 2 to 10 m/sec and temperatures from -20°C to 140°C. The purpose of the USCAR machine and test methodology is to encourage traction fluid development and to establish a common testing approach for fluid qualification. The machine utilizes custom software, which provides flexibility to conduct comprehensive traction fluid evaluations.

In recent years, the slip lock-up mechanism has been adopted widely, because of its fuel efficiency and its ability to improve NVH. This necessitates that the automatic transmission fluid (ATF) used in automatic transmissions with slip lock-up clutches requires anti-shudder performance characteristics. The test methods used to evaluate the anti-shudder performance of an ATF can be classified roughly into two types. One is specified to measure whether a μ-V slope of the ATF is positive or negative, the other is the evaluation of the shudder occurrence in the practical vehicle. The former are μ-V property tests from MERCON® V, ATF+4®, and JASO M349-98, the latter is the vehicle test from DEXRON®-III. Additionally, in the evaluation of the μ-V property, there are two tests using the modified SAE No.2 friction machine and the modified low velocity friction apparatus (LVFA).

In order to reveal the shifting mechanisms for CVT using a metal pushing V-belt, three shifting rates were introduced. The belt motion in the pulley groove was also characterized using mean coefficients of friction as parameters, which identify the slippage condition of the belt in the pulley groove. The experimental results showed that one of shifting rates, dR/ds was almost constant in the narrowing pulley regardless of both rotational speed and transmitted torque. Here, R is the belt pitch radius in the pulley and s is the length measured along the belt pitch line. This fact indicates that the shifting is primarily governed by elastic deformation of blocks of the belt. Power transmitting states were also evaluated using a different type of lubricating oil whose nominal coefficient of friction was higher than that for the conventional AT oil. The observed mean coefficients of friction vary due to oil although the basic response of the CVT unchanged.

Four forces act in rings for a metal pushing V-belt. These forces are: two kinds of intercepting forces which prevent blocks from going outside of pulleys (one caused by pulley thrust, the other caused by centrifugal force), frictional force acting between the rings and the blocks, and bending force in longitudinal direction. In the previous paper (1)(2)(3)(5), distribution of three forces, excluding centrifugal force, were presented at low belt speed. We successfully measured all four kinds of forces including centrifugal force continuously at practical operation conditions for layered rings. In this paper, distribution of these four forces on the innermost ring is described at steady states.