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Since it takes a long time to design motorcycles in order to prevent weaving and wobbling, which are self-excited oscillations, this paper aims to shorten the design process. The reason for the extended duration is that the weave and wobble strongly depend on ‘forward speed’ when the design variables are altered. Therefore, this paper focuses on speed and visualizes the region where self-excited oscillation does not occur for each design variable as a function of vehicle speed. The results demonstrate that at high speeds, the caster angle and steering damper are the only design variables for which this region exists near the design value. Due to the narrowness of these sweet spots, they become the most crucial variables in the design. However, this paper solely considers the caster angle as the most important design variable, as the steering damper adversely affects handling.

This paper considers the phenomenon that the self-steer speed when riders bank a motorcycle. This paper points out that this phenomenon originates from capsize mode. Further, it is specified that the first order differential equation representing capsize mode is included in the equation of motion of the steering system. Furthermore, it is specified that this differential equation is the first order differential equation for the roll angle. Therefore, as the roll angle increases, the roll angle further increases and the steering angle also changes, which is the mechanism of capsize mode. Finally, as a result of parameter studies, it is stated that the design parameters that most affect capsize mode were front and rear camber stiffness.

Grip feeling is an important facet in vehicle dynamics evaluation from a driver satisfaction and enjoyment standpoint. To improve grip feeling, we analyzed the subjective comments from test driver's about grip feeling and an evaluated human sensitivity to lateral motion. As a result, we found that drivers evaluate transient grip feeling according to the magnitude of lateral jerk. Next, we analyzed what vehicle parameters affect lateral jerk by using theoretical equations. As a result, we found that cornering power is an important parameter, especially the cornering power of rear tires as they can be create larger lateral jerk than can front tires.

An understanding of human sensitivity is an important factor in enhancing vehicle dynamics. The purpose of this study was to evaluate human sensitivity to vehicle dynamics, especially visual and motion sensitivity. The first step of this study involved the development of a human sensitivity evaluation system composed of a highly responsive six-degree-of-freedom motion device and a visual device with high spatial frequency resolution. This system is able to apply sensory and visual information to a test subject corresponding to that experienced during driving. Perceptional characteristics with regard to single motions were evaluated using this system.

Vehicle stability after releasing the accelerator during limit cornering (from now on “Tuck-in”) is the behavior that the turning radius of a vehicle gets smaller after releasing the accelerator. This paper presents that the main factors of yaw moment variation by releasing the accelerator are the change of lateral forces due to longitudinal transfer of normal loads, lateral shift of vehicle center of gravity due to vehicle roll and tire lateral deflection, and the change of lateral forces due to deceleration. It also shows that roll stiffness distribution and longitudinal acceleration have an influence through the formulation of turning radius ratio.

This paper introduces vehicle test method, data processing and result parameters of an objective evaluation method to quantify on-center handling at freeway driving. Vehicle test is conducted on a flat straight road with a low frequency sinusoidal steering angle input. The result consists of eleven parameters that describe relations of two quantities such as gain, non-linearity and lag time.

Attaining optimum balance between longitudinal compliance and sideforce compliance steer in a torsion beam suspension system is a challenging task. We developed a suspension in which the longitudinal compliance is almost doubled and the side force compliance steer amount is improved by using the link effect of toe control links. This suspension system has been developed to realize excellent controllability, stability, riding comfort, and road noise performance.

This paper examines the steering inputs that cause rear-wheel skid. First, we compare the front and rear side force at maximum lateral acceleration and thus distinguish rear-wheel skid from front-wheel skid. Next, we examine the affect of forward velocity on rear-wheel skid, and show that rear-wheel skid cannot occur below a given forward velocity. We use this velocity as an index of rear-wheel skid tendency and formulate it. This formula shows that the difference between front and rear axle trajectories strongly affects rear-wheel skid.