Study on Vehicle Rollover Prevention and Ride Comfort Based on AARB

When interfered by lateral acceleration or uneven road surface, a vehicle is prone to rollover. In this paper, the active anti-roll bar (hereinafter AARB) is self-designed and a six-degree-of-freedom vehicle dynamic model is established for rollover prevention and ride comfort improvement. In order to prevent the rollover and ensure the ride comfort of the vehicle, the linear quadratic (LQ) optimal controller is designed and the weights of the controller are optimized by particle swarm optimization algorithm (PSO). Furthermore, this paper carries out a series of simulation experiments which test the validity of the proposed control strategy in the aspects of body vertical acceleration, roll angle acceleration, roll rate, roll angle, vertical displacement of the suspension and tires, and AARB roll moment. Stimulations show that the method is effective in preventing the rollover and ensuring the ride comfort of a vehicle. Introduction Because of vehicle steering or uneven pavement, the traditional roll bar can not adjust roll angle stiffness of suspension in real time. For a vehicle with higher center of gravity, it is prone to causing excessive roll angle of a vehicle body and thus a rollover occurs. In rollover prevention, the following active control technologies----such as semi-active suspension [1], active suspension [2], active steering [3], differential brake [4] and AARB control [5], [6], ----are currently being applied. As the AARB can change the roll angle stiffness of the suspension timely to prevent vehicles from rolling over according to the steering and driving condition of the car, this control technique, compared with several others, can be more direct and effective in rollover prevention. Additionally, AARB has the advantages of low cost and easy application, so it has become a research focus. Many experts have done their research on AARB. Gaffney III et al. introduced an electro-hydraulic controlled AARB with double-loop control system. It was proved to be effective to prevent a rollover of the vehicle with an AARB in simulation and experiment tests [7]. K. JEON et al. utilized an electric control AARB, established a single degree freedom dynamic model, and applied the method of sliding mode control to stop a vehicle rollover [8]. Bal ́azs Varga et al. adopted LQ theory to calculate the required roll control torque of the hydraulically controlled AARB for light commercial vehicles [9]. Due to the poor lateral stability of air suspension vehicles, Li Junwei et al. adopted the variable stiffness AARB and gave an angle rigidity relational expression between the front suspension and the rear. The simulation demonstrated that the equipment could stop body roll effectively without influencing the ride comfort [10]. In above literatures, however, only the active stabilizer bar was considered in preventing rollover, and the influence from various parameters of rollover and ride comfort was not taken into comprehensive account. So, there are some limitations. To these shortages, this paper, considering the above influence, designs a LQ optimal controller and applies particle swarm optimization algorithm (PSO) to optimize the weight coefficient of the controller when vehicles disturbed by lateral acceleration and uneven road. 6th International Conference on Information Engineering for Mechanics and Materials (ICIMM 2016) © 2016. The authors Published by Atlantis Press 634 AARB structure and vehicle dynamic model AARB structure The schematic diagram of self-designed AARB is shown in Figure1. It is composed of a DC motor, a left harmonic gear mechanism, a right harmonic gear mechanism, a left semi-stabilizer bar, and a right semi-stabilizer bar. Motor armature shaft is connected both to the left wave generator of the harmonic gear and to the right one, so each wave generator is the driving member of the left and the right harmonic gear mechanisms respectively when the motor is rotating. In the left harmonic gear mechanism, the flexible gear is fixed to the shell, and the rigid gear is a follower; in the right harmonic gear mechanism, the rigid gear is fixed to the shell, and the flexible gear is a follower. So the transmission ratio of the left side of the harmonic gear is: 4 4 4 3 0 = h z z i z z z = − (1) And the transmission ratio of the right side of the harmonic gear is: 3 3 4 3 0 =h z z i z z z ′ ′ ′ = − ′ ′ − (2) z3 is the value of the flexible gear teeth of the left side harmonic gear; z4 is the value of the rigid gear teeth of the left side harmonic gear;z’3 is the value of the flexible gear teeth of the right side harmonic gear;z’4 is the value of the rigid gear teeth of the right side harmonic gear. In the expressions, 4 3 0 z z z = + , 4 3 0 z z z ′ ′ = + . z0 is the difference of the two teeth values between the flexible gear and the rigid gear of the harmonic gear mechanisms in both sides. In order to make the value of the output torque of left semi-stabilizer bar be equal to that of the right and make the direction of the output torque of left semi-stabilizer bar be opposite to that of the right, select 3 4 = z z ′ ,then h h i i′ = − . When a vehicle is interfered by lateral acceleration or uneven road surface, the controller controls the motor output torque to make the left and the right semi-stabilizer bar generate an output torque which varies with the body roll angle, the roll rate, and the suspension stroke, etc. The output torque generated by semi-stabilizer bars can reduce the rolling suspension stroke and the body acceleration of a vehicle. So, the driving safety and the ride comfort of the vehicle are greatly improved. Fig.1 The Schematic diagram of self-designed AARB 1, 1’-left and right semi-stabilizer bar 2-left wave generators 3-left flexible gear 4left rigid gear 2’right wave generators 3’-right flexible gear 4’-right rigid gear 5motor armature shaft 6-motor rotor 7-motor stator 8-shell 9,9’-left and right supports 10, 10’-left and right connecting arm