Shun'ichi Doi

Bifurcation in vehicle dynamics and robust front wheel steering control

A control strategy is proposed for designing a steering control for automotive vehicles to protect the vehicle from spin and to realize the improved cornering performance. The saturation characteristics of rear tires are modeled by a linear function with uncertainty terms of a special structure. The nonlinearity of the saturation is included in the part of uncertainty. The linear H/sup /spl infin// control theory is applied to the design of a front wheel steering controller which compensates the instability against the nonlinear uncertainty. The designed controller is shown to work quite well for nonlinear systems in achieving robust stability and protecting the vehicle from spin. Furthermore, the computer simulations show that the control improves cornering performance in critical motions. The motion realized by the controller resembles the one known as a counter steering which skilful drivers often use.

Vibration control apparatus

A thixotropic material is charged in a container. The container also holds a movable member which is placed in the thixotropic material so as to stir the thixotropic material. A force transmitting element is connected to the movable member. When an object, the vibration of which is to be controlled, is out of resonance, the amplitude of vibration is so small that the thixotropic material is in a gel state, thus presenting a comparatively large spring constant for the vibration control apparatus. As the excitation frequency is increased towards the resonance range, the amplitude of vibration is increased correspondingly, so that the movable member stirs the thixotropic material to generate stress in the latter, whereby the phase of the thixotropic material is changed from gel to sol. Consequently, the natural frequency of the vibration system, including the object and the vibration control apparatus, is lowered, thus averting resonance. It is thus possible to obtain vibration restraining or control effect over a wide range of excitation frequencies.

Proposal of an eco-driving assist system adaptive to driver's skill

The purpose of the present study is to develop an eco-driving assist system that is adaptive to a drivers skill and to demonstrate its effectiveness. The eco-driving assist system consists of a visual indicator illustrating the eco-driving. In the proposed adaptive system, the resolution of the indicator and the threshold of eco-driving are changed to adapt to the drivers skill. The proposed eco-driving system was installed in a driving simulator. Changes in driving behavior and the corresponding eco-driving scores, measured over five days, were investigated. As a comparison, experiments were conducted on a system without any level changes (a non-adaptive system) and on one without any assist system. In the results, eco-driving scores were higher with the assist systems than without them. The score with the adaptive system increased through the trial days, while no clear tendency was found with the non-adaptive system.

Regional frontal gray matter volume associated with executive function capacity as a risk factor for vehicle crashes in normal aging adults.

Although low executive functioning is a risk factor for vehicle crashes among elderly drivers, the neural basis of individual differences in this cognitive ability remains largely unknown. Here we aimed to examine regional frontal gray matter volume associated with executive functioning in normal aging individuals, using voxel-based morphometry (VBM). To this end, 39 community-dwelling elderly volunteers who drove a car on a daily basis participated in structural magnetic resonance imaging, and completed two questionnaires concerning executive functioning and risky driving tendencies in daily living. Consequently, we found that participants with low executive function capacity were prone to risky driving. Furthermore, VBM analysis revealed that lower executive function capacity was associated with smaller gray matter volume in the supplementary motor area (SMA). Thus, the current data suggest that SMA volume is a reliable predictor of individual differences in executive function capacity as a risk factor for vehicle crashes among elderly persons. The implication of our results is that regional frontal gray matter volume might underlie the variation in driving tendencies among elderly drivers. Therefore, detailed driving behavior assessments might be able to detect early neurodegenerative changes in the frontal lobe in normal aging adults.

Robust stabilization of vehicle dynamics by active front wheel steering control

The study of designing steering control systems for vehicles has attracted much attention, with the purpose of improving maneuverability and stability. Most of the vehicles models used to represent the dynamics were linear ones. Because of this, the control has to be restricted, at least theoretically, within a small range of steering angle, and may not be enough to compensate stability in critical motions. The purpose of this paper is to present a control strategy of the active front wheel steering system to protect the vehicle from spin and to realize the improved cornering performance. For this, the mechanism of vehicle spin behavior is analyzed and explained using concepts of bifurcation theory. The vehicle destabilization is shown to be caused by a saddle-node bifurcation and it depends heavily on a rear tire side force saturation. Based on these observations, the saturation characteristics of rear tires are modeled by a linear function with uncertainty terms of a special structure. Then the linear H/sup /spl infin// control theory is applied to design a front wheel steering controller which compensates the instability against the nonlinear uncertainty.

Can passengers' active head tilt decrease the severity of carsickness? Effect of head tilt on severity of motion sickness in a lateral acceleration environment

Objective: We investigated the effect of the passenger head-tilt strategy on the severity of carsickness in lateral acceleration situations in automobiles. Background: It is well known that the driver is generally less susceptible to carsickness than are the passengers. However, it is also known that the driver tilts his or her head toward the curve center when negotiating a curve, whereas the passengers head moves in the opposite direction. Therefore, we hypothesized that the head-tilt strategy has the effect of reducing the severity of carsickness. Method: A passenger car was driven on a quasi-oval track with a pylon slalom while the participant sat in the navigator seat. The experiment was terminated when either the participant felt the initial symptoms of motion sickness or the car finished 20 laps. In the natural head-tilt condition, the participants were instructed to sit naturally, to relax, and not to oppose the lateral acceleration intentionally. In the active head-tilt condition, the participants were asked to tilt their heads against the centrifugal acceleration, thus imitating the drivers head tilt. Results: The number of laps achieved in the active condition was significantly greater than that in the natural condition. In addition, the subjective ratings of motion sickness and symptoms in the active condition were significantly lower than those in the natural condition. Conclusion: We suggest that an active head tilt against centrifugal acceleration reduces the severity of motion sickness. Application: Potential applications of this study include development of a methodology to reduce carsickness.Objective: We investigated the effect of the passenger head-tilt strategy on the severity of carsickness in lateral acceleration situations in automobiles. Background: It is well known that the driver is generally less susceptible to carsickness than are the passengers. However, it is also known that the driver tilts his or her head toward the curve center when negotiating a curve, whereas the passenger’s head moves in the opposite direction. Therefore, we hypothesized that the head-tilt strategy has the effect of reducing the severity of carsickness. Method: A passenger car was driven on a quasi-oval track with a pylon slalom while the participant sat in the navigator seat. The experiment was terminated when either the participant felt the initial symptoms of motion sickness or the car finished 20 laps. In the natural head-tilt condition, the participants were instructed to sit naturally, to relax, and not to oppose the lateral acceleration intentionally. In the active head-tilt condition, the participants were asked to tilt their heads against the centrifugal acceleration, thus imitating the driver’s head tilt. Results: The number of laps achieved in the active condition was significantly greater than that in the natural condition. In addition, the subjective ratings of motion sickness and symptoms in the active condition were significantly lower than those in the natural condition. Conclusion: We suggest that an active head tilt against centrifugal acceleration reduces the severity of motion sickness. Application: Potential applications of this study include development of a methodology to reduce carsickness.

A deceleration control method of automobile for collision avoidance based on driver's perceptual risk

To reduce rear-end crash of automobiles, it is important to judge necessity of deceleration assistance as earlier as possible and initiate the assistance naturally. On the other hand, we have derived a mathematical model of drivers perceptual risk of proximity in car following situation and successfully derived driver deceleration model to describe deceleration patterns and brake initiation timing of expert driver. In this research, an automatic braking system for collision avoidance will be proposed based on the formulated brake profile model and brake initiation model of expert driver to realize smooth, secure brake assistance naturally. It will be shown that the proposed control method can generate smooth profile for various conditions. In addition, experimental results using a driving simulator will show validity of the proposed system based on subjective evaluation.

Consideration of a human dynamic characteristic and performance evaluation of an electric active suspension

A rotary actuator type electric active suspension system, adopted for the investigation, enable to control roll, pitch, and bounce. The system allows controlling the vehicle attitude by an inertial input logic while sky-hook logic improves ride comfort. Actual vehicle motion control effects on the driverspsila reaction were investigated. Driverspsila reaction differences were examined on the slalom driving under the active suspension-produced small and large roll angles. A roll oscillation simulator is set up in order to investigate influence of the roll angle which side acceleration of cornering does not act on. The simulator is applied to analyze the driverspsila adjusting characteristics under several roll angles and to examine driverspsila movement optimization. Analyzed results and consideration of the human characteristics are reported in the active suspension mounted vehicle case and the simulator case.

Effect of driver's head tilt strategy on motion sickness incidence.

Abstract Car drivers receive the acceleration stimulation and the rotational stimulation when negotiating with a curve. In such a situation, the driver controls his/her posture such as the head and the body appropriately. It is known that the driver tilts his/her head toward the curve direction while the passengers’ head movement is likely to occur in the opposite direction. There are some interpretations of the role of the drivers active head movement such as increasing visibility and decreasing of effect of the inertial force to the body including the trunk and the neck. The goals of this research are to understand relationship between head tilt strategy and motion sickness incidence and apply its result to the design of comfortable vehicle motion. First, we derive a mathematical model of the motion sickness incidence caused by the head movement in 3D space based on subjective vertical conflict. Then, we analyze effect of the head movement on decrease of motion sickness incidence using the mathematical model.

The Study of Characteristic of Attention in Depth of Drivers in Supposed Traffic Environment

The number of traffic accidents keeps increasing in China with the development of road traffic environments. From statistical data, it is well known that there are a lot of accidents at twilight time. The cause of these accidents is depending upon the shift of attention in depth according to the changes in twilight. Investigations of the characteristic of shift of attention in depth in three-dimensional (3-D) space by changing periphery luminance when the subjects were moving forward were carried out using a three-dimensional attention measurement system in order to examine the effects of luminance environment on the shift of attention. In the experiments, two kind of luminance condition were used, brightness condition and twilight condition. In each experiment, there were three kinds of clue condition: valid, invalid and neutral condition. It was the location of the appearance of the target relative to the fixation point. Observer moved forward at 0.44 m/s speed, and illuminance were 480~6801times and 95~1351times in the experimental device inner. The subjects task was to judge whether the target presented nearer than fixation point or further than it. Reaction times of the subjects on the clue were measured. As the results, it was clarified that (1) the visual adaptive ability of the subjects had a individual difference, (2) the shift of attention was faster from far to near than from near to far, (3) the reaction time was effected by the attention moved distance, (4) brightness has had very great influence upon the delay of reaction time of the drivers in traffic environment, and the delay of reaction time depended on the quantity of attention moved.