Research On The Hydraulic Active Suspension Of Cross-country Engineering Vehicle Based On The QFT Control

Since the 20th century, vehicle has entered a new period of development, because of the changes in the work environment, their, reliability and safety is also put forward higher requirements. Suspension works as an important assembly of vehicles plays a vital role on the overall performance of the project. The traditional suspension of Engineering vehicles are generally passive suspension stiffness, the passive suspension spring with a simple damping structure, no matter how the road changes, the stiffness coefficient of suspension still the same, and the body height is not adjustable. for the engineering vehicle this passive suspension is a obstructing to the development ofTherefore, this paper works to change the traditional structure of the suspension , introduce the concept of active suspension and independent suspension to the construction vehicles, develop the high-adjustable suspension system to improve the cross-country ability and stability of engineering vehicle. At the same time, the general use of the robot off-road suspension witch is height adjustable provides a good reference to the use of active suspension to the engineering vehicles.In this paper, we carry out the preparatory work for the national "863" project, "two degrees of freedom articulated off-road vehicle" , develop a hydraulic active suspension system witch have the adaptive capacity to the ground. research the structure and control of active suspension home and abroad, summarize the status and the level of active suspension technology. This suspension system use the articulated link structure and the hydraulic system witch have high system stiffness, and fast response characteristics, select the hydraulic cylinder as the active suspension actuator. As the hydraulic system is non-linear and the load changes largely, use the QFT control theory to design the controller of the suspension, develop a vehicle-mounted electronic control unit ECU of the automatic adjustment suspension system of off-road construction vehicle. The domestic suspension system of cross-country vehicle in general remain at the theoretical stage. We now have make real vehicle to carry out research, and shortened the distance between theoretical research and product development. The full text is divided into 6 chapters, each chapter are as follows:1. Introduce the origin of the subject and the significance of the study. This subject base on the national "863" project, introduce the concept of active suspension and independent suspension to the engineering vehicles, develop the high-adjustable suspension system to improve the cross-country ability and stability of engineering vehicle. Research the current domestic and foreign high adjustable active suspension. Discuss the viability of apply a hydraulic active suspension to the engineering vehicles. the main elements of research is to research and design a hydraulic active suspension system of off-road construction vehicle.2. Systematic analysis the structure and working principle of the off-road construction vehicle hydraulic suspension. The hydraulic suspension system is divided into three clear parts: an articulated mechanical structure, hydraulic circuit and the control unit ECU. Descript the work principle of each part in details. Qualitative analysis the performance of each part. Design the control system and control processes of the whole suspension, detailed description the of workflow the electronic control unit ECU.3. Do a detailed mathematical analysis on the part of the mechanical structure and the valve-cylinder system. Work out the mathematical model of the mechanical structure. Based on the dynamic equations and trigonometric functions, we build a nonlinear and simultaneous mathematical model of the. With the help of the matlab/simulink solver, Analysis the response of the mechanical structure model through different input frequency, Work out the changes of the complexity and unpredictable interference power.At present, the study of the control system of non-symmetric hydraulic cylinders with non-symmetric proportion valve is few. In this article we do a deep theoretical study of this typical hydraulic control system. With hydraulic static mechanics and fluid dynamics theory, respectively work out the pros and cons mathematical equation of this typical valve-cylinder system. and linear some non-linear equations using the Taylor expansion. Work out the mathematical model of the construction of the valve-cylinder system and transform into its transfer function, then do some qualitative analysis with its transfer function.4. QFT control theory is based on frequency domain analysis of the controller. To this cross-country vehicles, combining the parameters with experimental experience to solve the system linearization function. For this special vehicle suspension, constitute the control demand, that is, to meet the strict requirements of the tracking error in the low frequency band. Design the control system and pre-filter with the use of QFT toolbox in matlab. At the same time in simulink simulation, carry out the controller's response of frequency and time domain.5. Test the hydraulic active suspension of the Off-road vehicles. Based on vehicle prototype system, do a series test of the suspension dynamic response. Work out the tracking curve of the suspension to different frequency signals. Analysis the performance of the dynamic response of suspension and the elements witch may cause error qualitatively. The results showed that the tracking ability of the suspension system to input signal is well and the tracking error is in the tolerance.6. Proposed a number of deficiencies of the design of the control system for hydraulic active suspension of off-road construction vehicle, and in future research work can be improved.