Research Of ABS Algorithm For Multi-axle Vehicles And Hil Test

With the ever-growing of multi-axle vehicles' application in construction and national defense, people ask for higher safety performance for multi-axle vehicles. As a basic safety performance of vehicle driving safety, braking safety is put forward strict requirements by governments of all countries in the world. To further improve braking safety for a moving vehicle, anti-lock braking system(ABS) emerges as the time requires. As a kind of active safety system, ABS is able to reduce braking torque automatically when the wheel is going to lock so slip ratio of the wheel is kept in safe range effetely. As a result, steering ability of the vehicle is improved when a vehicle is steering with braking and dangerous situation such as drifting happens less during the process of braking. Currently, ABS is widely used on passenger cars, but on commercial vehicles, especially on multi-axle vehicles, its application and research are few. Compared to two-axle vehicles, multi-axle vehicles have longer chassis and larger load so increasing vehicle velocity gives larger challenge to multi-axle vehicles' safety. The longer frame will cause greater damaging to the vehicle itself and road safety. In addition, axle load calculation for multi-axle vehicles is much more complicated than two-axle vehicle so axle load calculation and road identification have significant meaning to effectively using of adhesion and reducing brake distance for a multi-axle vehicle brakes on butt road.Taking four-axle vehicles as an example, this dissertation has comprehensively introduced ABS algorithms for multi-axle vehicles including engineering PID control, sliding mode control, and so on. Based on these algorithms and combined with characteristics of ABS of multi-axle vehicles, this dissertation proposes a new sliding mode control strategy with fractional calculus for ABS of multi-axle vehicles. It also proposes an improved feedback control strategy for currently widely used ABS with on/off valves after researching control theory of nonlinear system. To further improve ABS control effect, fuzzy logic, typical road distance factor, and vicinity estimation are used to obtain optimal target slip ratio. The control strategies are based on slip ratio of wheel and slip ratio is calculated by wheel angular speed and vehicle longitudinal velocity, but vehicle longitudinal velocity can not be obtained through wheel angular speed sensors which are the only sensors that ABS has. So vehicle longitudinal velocity estimation is very important for control effect. This dissertation proposes a method of estimating vehicle states based on ESP sensors at first. Then it focuses on longitudinal dynamics and proposes a method based on vehicle acceleration and wheel speed sensors. After further simplication, it proposes another method based on ABS control signals and wheel speed signals. To further improve ABS performance, this dissertation proposes a distance factor based algorithm to estimate optimal slip ratio. Though a series of verification by software simulation and HIL simulation, algorithms proposed in this dissertation are proven to be effective.The research in this dissertation starts from building up dynamics model of multi-axle vehicles. The main difference between multi-axle vehicles and two-axle vehicles is the calculation of axle load, so this dissertation proposes a method of calculating axle load based on suspension stiffness and damp. Then, combied with models of brake system, tire-road system, the whole vehicle system is simulated and compared with commercial models. Then a single wheel model is built. Control with fixed target slip ratio is researched based on it. According to single wheel control strategy and optimal slip ratio estimation, vehicle speed, wheel speed, wheel angular acceleration, tire-road friction are the informations which are necessary. So this dissertation proposes an method of states estimation based on many sensors at first. Then it considers longitudinal dynamics only and finally proposes a method based on ABS control signals and wheel speed signals. Finally, every algorithm is verified through HIL simulation.