Ryouhei Hayama

Fault-tolerant automobile steering based on diversity of steer-by-wire, braking and acceleration

Steer-by-wire (SBW) systems, which have no mechanical linkage between the steering wheel and front wheels, are expected to improve vehicle safety through better steering capability. SBW system failures, however, can cause hazardous driving situations. This paper introduces fault-tolerant architecture based on diversified steering mechanisms consisting of SBW backed up with steering by braking and acceleration during SBW failures. These backup steering functions are chosen according to drivers intention of deceleration and acceleration. A loss of SBW function during front-obstacle avoidance on a straight highway is investigated by driving simulator experiments. The results show that the driver can maneuver the vehicle by the steering wheel during the SBW failures. Both cost and volume increase by excessive redundancy within SBW is avoided by the diversified design, thus facilitating SBW application on new-generation vehicles.

Resistance torque control for steer-by-wire system to improve human–machine interface

A steer-by-wire system, which has no mechanical constraints between steering wheel and front wheel, is expected to improve steering performance. The mechanical resistance torque is not transmitted from the front wheel to the steering wheel, and it is essential to simulate the torque around the steering wheel for better human-machine interface. Previous studies investigated resistance torque control originating from vehicle behaviour variables such as yaw rate and lateral acceleration. However, other variables such as steering wheel angle and front wheel actuation force are also good candidate sources to generate resistance torque. In this paper, first, four general guidelines are introduced to evaluate three types of resistance torques, i.e., the steering wheel angle origin, the steering force origin and the vehicle behaviour origin. First two guidelines are for ‘driver-made’ phase to make a turn, while the third guideline is for ‘vehicle-made’ phase to return to straight driving and the fourth one is the applicability guideline. Satisfaction of these guidelines by each of the three resistance torques is examined by the actual vehicle experiment. A necessity of combining these three types of resistance torques is indicated as a future subject.

Preliminary Research on Muscle Activity in Driver’s Steering Maneuver for Driver’s Assistance System Evaluation

The quantification of the driver’s workload to complement the subjective evaluation is required in order to evaluate the driver assistant system. Preliminary investigation results of muscle behavior during steering maneuver have been described. The role and the feature of muscle activities in simulated steering conditions have been clarified. Driver tends to maneuver with “push steering” in both clockwise direction and counter-clockwise direction. Muscle alternation and co-contraction between the two muscles corresponding to the opposite one could be seen at the change of the torque directions. According to the result, the driver’s steering workload might be estimated by evaluating the simultaneous activities of pectoralis clavicular and anterior deltoid of the both arms. The result of this research can be considered to be useful for the evolution of driver assistant system. Furthermore, it would contribute to spread the system and improve its performance. It might contribute to reduce traffic accidents as well.

A method to set the target on-centre steering force characteristic

In this paper, a method to set the target on-centre steering force characteristic is described. First, both the linear correlations and the non-linear correlations between subjective evaluations and objective metrics were established. During this process, subjective and objective evaluation tests regarding the on-centre steering force characteristic were conducted on a moving-base driving simulator by 15 experienced drivers. To ensure the reliability of the subjective ratings, a method to evaluate the ratings was introduced. Then the linear correlations and the non-linear correlations were analysed using multiple linear regression analysis and a neural network respectively. Second, by setting the desired subjective ratings as an optimization goal, target objective metrics were obtained on the basis of either the linear correlations or the non-linear correlations by means of non-linear programming. The target on-centre steering force characteristic was therefore designed on the basis of the target objective metrics. The results showed that the target on-centre steering force characteristic obtained from the linear correlations was quite similar to that obtained from the non-linear correlations. Also, it was verified that the target on-centre steering force characteristic matched the drivers’ preferences. From the correlations and the target on-centre steering force characteristic, engineers can establish the ratings of subjective evaluations and determine how to design the system to meet the target during the virtual design process. It shows a great potential in assisting the engineers to design a good steering feel at the early stages of the development process. Furthermore, the feasibility of this proposed method to allow customers to customize the on-centre steering force characteristic was explored. During this process, a fixed-base driving simulator was used instead of a moving-base driving simulator for cost reasons.