International Journal of Vehicle Autonomous Systems (4 papers in press)
Three-axle commercial vehicle with enhanced functionality and steering redundancy
by Dan Williams
Abstract: This paper presents a new means of steering redundancy for autonomous three-axle vehicles that also cost effectively increases vehicle functionality. Functional enhancements to increase maneuverability and decrease tyre wear are already appreciated in niche vehicle markets and are reviewed in this work. Steering the rear axle to provide redundancy in event of a primary steering axle failure has recently been suggested. This prior work is built upon to present a new three-axle vehicle configuration that improves maneuverability, increases payload capacity, and provides better redundant directional control while maintaining the tyre wear improvements existing in rear axle steer vehicles. Some of these same benefits could be achieved by steering the rear of a two-axle vehicle, but it is shown that the concept creates more value when applied to three-axle vehicles, thereby uniquely improving the value proposition for autonomous commercial vehicles.
Keywords: autonomous vehicles; commercial vehicles; vehicle dynamics; rear axle steer.
Estimation of vehicle sideslip angle and individual tyre-road forces based on tyre friction circle concept
by Hui Lu, Qingwei Liu, Yue Shi, Fan Yu
Abstract: The real time information of vehicle sideslip angle and tyre-road forces of individual wheels can help advanced vehicle chassis control systems to enhance vehicle handling, stability and safety. But in practice, these state variables are difficult to measure directly for technical and economic reasons. In order to esti-mate these states, this paper proposes an observer based on the Extended Kalman Filter (EKF) by using a 7-DOF vehicle model. According to the Dugoffs tyre model, the lateral force can be expressed by a function of the longitudinal force with the knowledge of tyre work condition. Based on this concept, the reference vehicle model is modified to identify the lateral forces of each braked wheel without the online information of vertical load and tyre-road friction coefficient. The simulation results indicate that the longitudinal and lateral forces of each wheel can be well estimated under combined cornering and braking conditions.
Keywords: tyre force estimation; vehicle sideslip angle estimation; tyre friction circle concept; extended Kalman filter.
Modelling and optimisation of active front wheel steering system control for armoured vehicle for firing disturbance rejection
by Mazuan Mansor, Khisbullah Hudha, Zulkiffli Abd Kadir, Noor Hafizah Amer, Vimal Rau Aparow
Abstract: While firing on the move, the handling performance of an armoured vehicle is affected, thus causing it to lose its directional stability. This is owing to an impulse force generated at the centre of the gun turret, which can produce an unwanted yaw moment at the centre of gravity of the armoured vehicle. Hence, in order to reject the unwanted yaw moment, a new hybrid control strategy known as neural-PI controller is introduced by combining a neural network system and a conventional PI controller. This active system, furthermore, is intended mainly to reduce the yaw rate and to enhance the handling performance by providing the steering correction angle to the conventional steering system. Moreover, this paper develops 14 DOF of armoured vehicle and 2 DOF of Pitman arm steering system. Also included in this paper is the dynamic equation of the planetary gear system used as the active front wheel steering actuator implemented in the vehicle model, which is derived by using the Euler-Lagrange method. Other than that, determination of the most suitable activation function to be implemented in the neural-PI controller is carried out and optimised by using the genetic algorithm method. The performance of the controller is further evaluated by comparing the conventional PI controller with the neural-PI controller implemented with different activation functions.
Keywords: 14 DOF; active front wheel steering; firing disturbance; neural network; genetic algorithm; activation function.
Global path planning for autonomous vehicles in off-road environments via an A-star algorithm
by Qinghe Liu, Lijun Zhao, Zhibin Tan, Wen Chen
Abstract: In order to solve the problem of global path planning for autonomous vehicles in off-road environments, an improved A-star path-searching algorithm that considers the vehicle powertrain and the fuel economy performance is proposed in this paper. First, we discuss the digital elevation model (DEM) matrix adopted to describe the off-road earth surface generally. Then, we define three important concepts regarding path planners on the basis of the DEM matrix. Second, we design a novel comprehensive cost function for the A-star algorithm with shortest path distance and minimum fuel consumption. Finally, the algorithm is simulated on a DEM through several different missions. The simulation results show that the proposed algorithm is effective and robust in finding the global path in complex terrains.
Keywords: A-star algorithms; path planning; autonomous vehicles; digital elevation model.