1、An Application of Nonlinear PID Control to a Class of Truck ABS Problems Fangjun Jiang Ford Motor Company, Product Development Center, GB-E65, MD 19920901 Oakwood Blvd. Dearborn, MI 48124 Zhiqiang Gao The Applied Control Research LaboratoryDepartment of Electrical and Computer Engineering Cleveland
2、State University, Cleveland, Oh 44115 Abstract: A new NPID (Nonlinear Proportional-Integral-Differential) control algorithm is applied to a class of truck ABS (Anti-lock Brake System) problems. The NPID algorithm combines the advantages of robust control and easy tuning. Simulation results at variou
3、s situations using TruckSim show that NPID controller has shorter stopping distance and better velocity performance than the conventional PID controller and a loop-shaping controller. Keywords: Nonlinear, PID, ABS. 1. Introduction ABS for commercial vehicles appeared on the market in 1960s and began
4、 to grow fast in 1970s with the technologies of microcomputers and electronics 1. ABS is recognized as an important contribution to road safety. It is now available in almost all types of vehicles. The automotive industry is continuously developing new generations of ABS. The technologies of ABS are
5、 also applied in TCS (Traction Control System) and VDSC (Vehicle Dynamic Stability Control) It is well known that wheels will slip and lockup during severe braking or when braking on a slippery road surface (wet, icy, etc.). This usually causes a long stopping distance and sometimes the vehicle will
6、 lose steering stability. The objective of ABS is to prevent wheels from lockup and achieve minimum stopping distance while maintaining good steering stability during braking. The wheel slip is defined as: VRS V （ 1.1） where S, , R and V denote the wheel slip, the wheel angular velocity, the wheel r
7、olling radius, and the vehicle forward velocity, respectively. In normal driving conditions, V R therefore S 0. In severe braking, it is common to have = 0 while V 0 , or S = 1, which is called wheel lockup. Wheel lockup is undesirable since it prolongs the stopping distance and causes the loss of d
8、irection control. 1.1 A Class of Truck ABS Problems The objective of ABS is to manipulate the wheel slip so that a maximum friction force is obtained and the steering stability (also known as the lateral stability) is maintained. That is, to make the vehicle stop in the shortest distance possible wh
9、ile maintaining the directional control. It is well known that the friction coefficient, , is a nonlinear function of the slip, S. The ideal goal for the control design is to regulate the wheel velocity, , such that an optimal slip, which corresponds to the maximum friction, is obtained. For the sak
10、e of simplicity, however, it is very common in industry to set a desired slip to .2. Given the vehicle velocity, V, and the wheel radius R, the ABS control problem becomes regulating such that the slip in (1.1) reaches a desired value, such as .2 In this paper, the control design is focused on a cla
11、ss of truck ABS problems, which pose a few unique challenges, different from passenger cars. 1. The actuator of the truck ABS is a pneumatic brake system, which is typically slower in response and harder to control than a hydraulic brake system. The control action of the brake system is discrete. Th
12、e brake pressure is controlled by discrete valves (open or close). The brake pressure can be controlled to increase, hold constant or decrease. Through PWM (Pulse Width Modulation), the actions of the discrete valves are mapped into a continues analog control signal ranging from 1 to +1, where 1 means fully exhausting pressure, +1 means fully building up pressure and 0 means holding pressure as constant. 2. The measurement of the brake pressure is not available, which makes the control of the pneumatic brake system even more difficult. The
