Study on Low-Speed Steering Resistance Torque of Vehicles Considering Friction between Tire and Pavement

Abstract

Electric power steering (EPS) systems under existing vehicle power systems cannot provide enough power for heavy-duty commercial vehicles under pivot or low-speed steering conditions. To solve this problem, the paper proposes an EPS system that is based on the hybrid power system constituted by the vehicle power system and the supercapacitor in parallel. In order to provide a theoretical basis for the intervention and withdrawal mechanisms of a super-capacitor in the new EPS, the law of steering resistance torque at a low or extremely low vehicle speed should be explored. Firstly, the finite element model of tire/pavement was established to conduct the simulation and calculation of the low-speed steering friction force between the tire and pavement, and to obtain the fitting expression of the equivalent steering friction coefficient with the running speed of the tire. Secondly, the expression of the steering friction torque was deduced based on the calculus theory and mathematical model of the low-speed steering resistance torque, including the steering friction torque and aligning torques, established to conduct the simulation of the equivalent resistance torque applied on a steering column under low-speed condition. Subsequently, the real vehicle experiments were carried out and comparisons of the experimental results and simulation results was performed. The consistency indicated that the model of low-speed steering resistance torque had a high accuracy. Finally, the law of low-speed steering resistance torque with a vehicle speed and steering wheel angle were analyzed according to the 3D surface plot drawn from the simulation results.

Optimization of Energy Management Strategy for the EPS with Hybrid Power Supply Based on PSO Algorithm

“…Finally, the real-time current fluctuation is obtained by accumulating the real-time I g in the PSO program. 6 and high I . According to these inputs, the energy management strategy program, which is interpreted to Matlab code based on Table 1, calculates and distributes the output current of the VPS g I and the charging current sc C I − or discharging current sc D I − of SC.…”

“…In this condition, the power/current requirement for EPS is far beyond the power supply capacity of VPS. Vehicles usually run in a medium or high speed, when the VPS can provide sufficient current to overcome the corresponding small steering resistance torque [6]. Therefore, it is necessary to focus on solving the problem of insufficient power provided by the VPS in the vehicles when turning at low speeds to promote the application of EPS on heavy-duty vehicles.…”

Steady-State Steering Characteristics of Mathematical Model for Semitrailer Based on Variations in Camber Parameters

“…where M ϕ 1 and M ϕ 2 are the roll torques of the tractor and trailer, respectively; h 1 and h 2 are the heights of the tractor and trailer centroids, respectively (m); and a Y 1 and a Y 2 are the lateral accelerations for the tractor and trailer, respectively (m/s 2 ). In this case, the variations in the camber angle caused by body roll and lateral forces can be calculated using [21]…”

Multi-Mode Switching Control of the EPS With Hybrid Power Supply

“…Considering the maximum power which the vehicle power supply can provide to the steering motor, the maximum assistant torque of the steering motor is equal to the certain threshold of steering resistance torque. According to the law of steering resistance torque at low speed [23], the steering angle and vehicle speed in critical state are obtained as shown in the TABLE 2.…”