| Off-road vehicles is a kind of mobile machinery driving on the roads laid down by the non-human,their off-road performance is an important indicator of off-road vehicles mobility,which is defined as the ability to continue driving under the condition that vehicles is off roads,that is,the crossability of vehicles on the complex roads.The traditional method of improving off-road vehicles' off-road performance are limited to simply improving the drivability of drive system,or simply changing the operating modes and control performance of suspension system,but these can't make the vehicles' off-road performance to achieve a qualitative change.In recent years,hydraulic transmission and control devices increasingly have become a indispensable part of vehicles and other mobile machinery,especially for the engineering machinery industry which mostly needs frequent operations in the field, including driving,steering,successful application on the suspension,providing the science and technology innovation of off-road mobile machinery with new ideas and advanced techniques.Now at home and abroad in the study of off-road vehicles,the driving structure is mainly embodied in the wheel or the wheel-leg;the structural form is mainly in the electric type or the combination of electric type and mechanical type.The study of full-hydraulic off-road vehicles(the hydraulic system control the drive and suspension system) is relatively few.However,the wide application of hydraulic technology has become an important symbol of modernization in machine,and the use of hydraulic motor-driven devices in a variety of off-road vehicles has been very common.And the developed oil-gas suspension in which the hydraulic technology is as the core has become the first choice of flexible suspension in a modern high-speed off-road vehicles.The full-hydraulic active suspension device is also slowly developing.Thus,the achievement of high-performance all-terrain hydraulic off-road vehicles has become a reality.The following hydraulic parts of drive system and suspension system in full-hydraulic off-road vehicles are discussed separately.Hydraulic drive means that the mechanical energy exported from engine(internal combustion engine or motor) can be converted into the hydraulic energy in the hydraulic pump,through the pipings and control valves,etc,in the hydraulic motor the energy can be reconverted to overcome the load torque and into the mechanical energy to achieve the required speed,and the motor directly or indirectly exports the mechanical energy to drive the wheels(or track) rotate,in order to achieve the purpose of driving vehicles.The use of hydraulic drive technology in mobile machinery has two main advantages:one is the regulatory aspect,namely,the excellent speed governing performance,the capacity of direct steering with load,with load change directly to the capacity,the capacity of overload protection,the operational comfort and so on.The other is the layout aspect,embodies in its flexible layout to adapt to the diversity of morphological changes of main unit,or conversely, the use of hydraulic drive technology promotes the morphological diversity and personality development of main unit.Hydraulic pump and motor can be installed in the independent hydraulic transmission in different parts of main unit,this can more fully exploit the advantages of both aspects,and thus become the current mainstream form of transmission of a variety of hydraulic components.Among them,particularly the way of hydraulic drive that the output components(hydraulic motor) are directly installed in the close proximity to the drive wheel has a far-reaching impact on the the development of mechanical structures of vehicles and mobile machinery.Suspension,as one of the most important assemblies in modern vehicles,plays a very important role in the design and use of vehicles.Over the years,the vehicles has used the passive suspension,but also because of its difficulty in synchronously obtaining the good vehicle ride comfort and the handling stability,especially these special vehicles which need frequent operations in the field,the passive suspension's limited travel and the capacity of passive adaptation of roads,to some extent restrict the vehicles' crossability and have an impact on vehicles' off-road performance.However,with the development of hydraulic technology,especially the constant update and improvement of electro-hydraulic proportional technology,the hydraulic active suspension is gradually being paid attention by researchers in various countries.Because the electro-hydraulic proportional control system has:1) the hydraulic actuator's high power-weight ratio and torque-moment of inertia ratio, the high power transmission density;2) the high load rigidity,the high precision;3) can safely,reliably and fast realize the frequent starting and braking with load,can carry out positive,and reverse linear or rotary motion and power control,but also has great speed range;and because of the use of incompressible fluid,then the sensitivity of response is high and so on.Therefore,using electro-hydraulic proportional control technology in suspension system,the vehicles in the driving process has a obvious damping effect,can automatically level the frame in the light of the rugged road,raise or lower the height of frame in the view of needs,in order to improve driving performance,crossability and other characteristics,this is the main direction of future development of suspension system.This paper did the preliminary design work of national "863" project(item number: 2007AA04Z208),independently developed the prototype of hydraulic off-road vehicles' chassis system.Unlike the synchronous drive technology applied in the previous drive system,this system used the hydraulic resistance control technology to make the flow assign automatically,in order to achieve the balanced traction drive of wheels,and significantly improve the traction efficiency of vehicles;and this system used the hydraulic cylinder controlled by the QFT control mode,which is based on the frequency domain analysis and has a strong robustness,to achieve the suspension system with a very strong barrier property. This paper has high research value for the the development of off-road vehicles in our country.This paper mainly conducted the following research work on hydraulic off-road vehicles' chassis system:1.Independently developed and designed the prototype of hydraulic off-road vehicles' chassis system.2.Analysed the current situation of hydraulic drive system and independent suspension system of domestic and international off-road vehicles,introduced several hydraulic suspension systems on the chassis of off-road vehicles driving on any road,which are being studied or have already been completed at home and abroad.And illustrated the purpose and meaning of studying the hydraulic off-road vehicles' chassis system.3.Compared with the traditional synchronous drive vehicles,put forward a concept of balanced traction drive system,made a detailed discussion on the working principle of hydraulic drive system with balanced traction,and according to the qualitative and quantitative analysis,theoretically described that using the hydraulic resistance control technology can improve the traction efficiency of drive system,and enhance the the vehicles' power performance,crossability and so on.Theoretically analysed the mechanical structure,hydraulic system and control unit of suspension system.Because of the complex structure,the strong outside interference of suspension system,the non-linear of hydraulic proportional system and other factors,used the QFT controller based on the frequency domain analysis to control the suspension system,through the suspension assembly control flow chart,discussed in detail the whole control process of suspension system.4.Analysed the load characteristics that variable displacement pump controls the constant displacement motor,and drew the simulation curve of mutual steady-state relations among the motor speed,the pump's theoretical discharge and the external load torque.On the basis of the wheel-ground contact angle,established the mechanical model of wheel,and through the pump-controlled motor and throttle principle established the hydraulic system model,finally did the simulation analysis of the entire drive system model.The results show that compared with synchronous drive system,the balanced traction drive system can greatly improve the traction efficiency of drive system,and enhance the the vehicles' power performance and crossability.5.Established the mathematical model of partial mechanical structure of hydraulic suspension,combined the trigonometric functions with the dynamical equations to build the partial nonlinear mathematical model of mechanical structure of suspension,then did the simulation analysis,by inputting response signals of different frequency to the suspension system,analysed the regularity for change of complex and unpredictable interference.Also through the theoretical analysis of suspension's mechanical structure and hydraulic system,derived non-linear mathematical model of single-suspension control system;and on the basis of the established model,using the conventional PID control technology,analysed the impact of nonlinear factors of proportional control system in the condition of exterior interference on system performance,the simulation results show that necessity of studying the non-linearity of system and intelligent control strategy,lay the mathematical model foundation for the follow-up research on the control algorithm of suspension system.6.In accordance with the goal,which this paper require the chassis system to accomplish,set the performance indicators of suspension system;established the non-linear theoretical model of the system,set the ranges of relevant parameters,through the nonlinear model that parameters change in it,obtained a series of inputs in the light of the required outputs, and by estimating the rational transfer function obtained a series of rational linear transfer function,got the uncertain aggregate of controlled object;by using QFT robust toolbox designed the QFT robust controller for single-suspension system,and did the simulation analysis of performance of control system in the light of closed-loop frequency response indicators of off-road vehicles' chassis system.The results show that,QFT robust controller has a stronger ability to suppress all sorts of interference,has a strong robustness in view of outside interferences and the non-linear parameter perturbations of system,to make the performances of the system step response,the square wave response and sinusoidal frequency which are represented as the performance of system performance fully meet the specified requirement of design specification.7.Gave two sets of hardware used in the actual system,designed the software of suspension test systems;tested the drive system,compared the result of synchronous drive with the result of balanced traction drive,verified the analysis in Chapter 2 that the balanced traction drive is superior to synchronous drive in improving the efficiency of vehicles,but also verified the theoretical analysis of Chapter 3 is correct;and test the suspension systems again,respectively test three cases,including the system is in no load,random load and actual random load,the test results show that after using the hydraulic independent suspension system and control strategy proposed in this paper,the control performance of loader is greatly enhanced,at the same time this can improve the performance of vehicles' crossability.The principal innovation of this paper are as follows:1.Put forward a concept of hydraulic balanced traction drive system.Made a detailed discussion on the working principle of hydraulic drive system with balanced traction,and according to the qualitative and quantitative analysis,theoretically described that using the hydraulic resistance control technology can improve the traction efficiency of drive system,and enhance the the vehicles' power performance,crossability and so on.2.On the basis of the wheel-ground contact angle,established the mechanical model of wheel,and through the pump-controlled motor and throttle principle,established the model of balanced traction drive system.The simulation and experimental results show that,compared with synchronous drive system,the balanced traction drive system can greatly improve the vehicles' traction efficiency,and enhance the the vehicles' power performance and crossability.3.Used the QFT robust controller based on the frequency domain analysis to control the suspension system.And in the light of condition that off-road vehicles often drive on the wild,complex and unknown to road,QFT robust controller has a stronger ability to suppress all sorts of interference,has a strong robustness in view of non-linear parameter perturbations of system.The simulation and experiment results show that,using the QFT robust controller can make the response time faster,anti-interference ability stronger,also can greatly meet the actual needs of suspension system. |
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