Study Of The Cooperative Chassis Control System Theory And Technology Based On The Top Level Design

Vehicle electronic chassis control system is made up of several sub-control systems, which affect each other and the improvement of vehicle overall performance is dependent on the cooperation of all those sub-control systems. The cooperation of those sub-systems is good for sharing of hardware and software of sub-system integration of vehicle chassis, energy management and information exchange so as meet higher requirements on safety, comfortableness and economy to realize integration, intelligence and networking, therefore, it is the main direction towards development of vehicle technology. Researchers at home and abroad have completed a lot of researches on the vehicle chassis integrated control theory and technology but a sound theory and system are yet to be established from the perspective of methodology.As the two key parts, the steering and suspension are relatively independent and easy to be controlled, but the two are associated with tire, which is the nonlinear system and interconnected with each other. This paper gives a qualitative and quantitative study on the relationship between side force and vertical force of tire to give full play to the impact on and tire performance with the steering and suspension as the subject. In addition, it provides cooperative integrated control study with the use of top-down top-level design concept to reduce or eliminate the conflict among all sub-systems by overall arrangement to complement each other’s advantages of all sub-systems. By thus doing, the variation in vehicle body posture due to change of driving intention and external environmental influence can be optimized to the fullest extent and the driving smoothness and handling stability can be improved at the same time. Based on that train of thought, the paper is mainly developed control of semi-active suspension, electric power steering control and monitoring of tire conditions and system integrated control.The paper establishes a coupled neural network model of side force and vertical force of tire. On the basis of s series of tests on tire cornering characteristics under various operating conditions carried out on the tire ground pressure test bed, the relationship among the cornering characteristics and cornering angle, wheel speed, vertical load and charge pressure etc. is analyzed. And then,588samples are selected and those data points are regarded as network characteristic parameters. After that, a self-adaptive neural network model is trained and established to lay a theoretical foundation for analysis of suspension and steering mechanism with the use of BFGS method for parameter identification and network approximation and by means of comparatively validation with magic formula tire model.The paper also builds a vehicle multi-body dynamics model, including steering and suspension kinematics, non-linear characteristics of elastic mechanics and compares the model with actual vehicle. At the same time, the relationship between stepping motor rotation angle and damping force of shock absorber in the semi-active suspension is determined via bench test so as to provide basis for design of semi-active suspension control and integrated controller.The paper analyzes the factors which affect yaw rate and studies the non-linear relationship between the yaw rate and angle of roll by representing the operating stability of vehicles under different speed and different coefficient of road adhesion as stability index in the steering process. In addition, the impact on overall performance of the vehicle brought about by the coupled system is analyzed on the basis of the study of correlation of performance indexes under transient response. The paper proposes the top-level design concept of vehicle chassis cooperative control and builds the framework of cooperative control of top-down semi-active suspension and electric power steering. It provides a top-level design of chassis system for semi-active suspension (SAS) and electric power steering (EPS) as per the operating conditions according to the coupling mechanism of suspension and steering and with reference to driving intention and vehicle condition and divides the chassis cooperative system into four sub-systems:tire sub-system (TYPE), semi-active suspension sub-system (SAS), electric power steering sub-system (EPS) and top-level sub-system (SYS). The fuzzy relational cooperation network is introduced for each sub-system as the cooperative mechanism to deal with the coordination and cooperation so as to determine the percentage of fuzzy weight of each sub-system in real time.A unified bottom sub-system based on perception, conviction and intention is designed. Considering the requirements of semi-active suspension control system, switch and communication between the smoothness, operating stability and safety is realized, a SAS sub-system is established and design of damping shock absorber with adjustable throttling mouth is improved; due to complicate and changeable working conditions with high real-time demand during operation of the electric power steering, the EPS sub-system is established to realize fuzzy control of switch of multi-conditions; the TYRE sub-system is established in light of the requirement of calculation of force of tires during driving and alarming of various abnormalities (such as tire leakage, under-pressure and over-pressure and over-temperature) and inflating valve provided with automatic pressure measurement developed independently to replace the current tire pressure sensor. A test bed including tire, suspension and steering and a simulation system are designed. Several joint simulation tests under step-input conditions such as random road, pylon course slalom test, lemniscate test and monopulse angle are made based on the system model established in accordance with principles of multi-body dynamics and in combination of controller model. After the tests, the results under different control method are compared and analyzed to check the validity of control algorithm. A rapid prototype simulation system composed of dSPACE and hardware connections is set up to verify the correctness and effectiveness of controllers by comparison with results of the joint stimulation tests under same working conditions.Hardware and software design of cooperative chassis system is made on the basis of FlexRay network and the damping shock absorber with adjustable throttling mouth are improved and inflating valves provided with automatic pressure measurement to replace the current tire pressure sensors are developed independently. Finally, the cooperative controller of vehicle chassis system is developed and tested after installing on the vehicle and the correctness control system and reliability of hardware design is verified by comparison with test results of the rapid prototype control system.The results show that the cooperative control of vehicle chassis system based on top design could meet the requirements of different subsystems under various driving conditions. Meanwhile, the cooperation and coordination of multi-systems during the cooperative process is also achieved. Compared with the traditional hierarchical control, the RMS values of the body vertical acceleration and the dynamic deflection of the front and rear suspension is improved to different degrees in the experiment with random road excitations. In the pylon course slalom test, though the average peak value of steering wheel angle is reduced slightly, the average peak value of steering wheel torque is reduced by13.31%, and the average peak value of yaw velocity is increased by9.77%.The average peak value of lateral acceleration is also reduced by10.01%. In the lemniscate test, when the steering is performed on low adhesion road, the handling torque is decreased slightly. However, during the aligning process, the handling torque is increased. Both ride comfort and handing performance is ensured. In the complex conditions test, the proposed controller effectively solves the limitation of taking many performance indicators into account, such as the body vertical acceleration, body roll angle, body pitch angle and yaw velocity, etc, which can’t be avoided by traditional hierarchical control. Therefore, the integrated chassis system with combining the top-level design and collaborative control can autonomous coordinate the system internal resources and attenuate the contradictions and conflicts between different subsystems, which achieve the global optimization of complex chassis system based on guaranteeing the full exertion of subsystem functions. The proposed chassis system gives consideration to both the vehicle handling stability and ride comfort and significantly improved the comprehensive performance of the vehicle.