| The hydraulic transmission system composed of the hydraulic torque converter as the main component is widely used in passenger,agricultural,engineering,military,and other vehicles because of its advantages of flexible transmission,low-speed high-torque characteristic,self-adaptive adjustment of speed ratio to an external load and so on.However,the efficiency of the hydraulic transmission system is not high.The hydraulic torque converter mainly relies on the change of the kinetic energy of the working fluid to transfer energy,and the torque of the engine undergoes two energy transformations at the hydraulic torque converter,thus reducing the transmission efficiency of the hydraulic transmission system.The hydraulic split transmission improves the transmission efficiency of the hydraulic transmission system to a certain extent.However,the split transmission greatly reduces the low-speed high-torque characteristic of the hydraulic torque converter,which makes the hydraulic transmission system unable to adapt to the complex and changeable loads.In addition,the characteristics of agricultural,engineering,and military vehicles are that they need to work when they are walking;that is,the power of the engine is not only used to drive the vehicle but also needs the hydraulic system to drive the working device.Due to the high power of the driving device,which usually accounts for 40%-60% of engine power,the matching of the hydraulic transmission system and engine can be divided into full power matching and partial power matching.The demand of capacity coefficient of the hydraulic transmission system is different between full power matching and partial power matching.However,the capacity coefficient of the torque converter is fixed,so the hydraulic transmission system can not take full power matching and partial power matching into account.Combined with the analysis of the above reasons,based on retaining the low-speed high-torque characteristic of the hydraulic torque converter,improving the transmission efficiency of the hydraulic transmission system has special capacity characteristics,which can give consideration to the research of full power matching and partial power matching,which is the key and difficult problem to promote the wider application of the hydraulic transmission system.In this paper,the project " Design Theory and Control Method of New Return Variable Transmission System" is supported by National Natural Science Foundation of China(Project No.: 51875055),aiming at the problems of low transmission efficiency of hydraulic torque converter,fixed capacity coefficient unable to take full power matching and partial power matching into account,and hydraulic shunt transmission system unable to retain low-speed high-torque characteristic,which hinder the wider application of hydraulic transmission system,a power reflux hydraulic transmission system with capacity adjustment device is proposed.The structure uses the power return technology to improve the transmission efficiency of the hydraulic transmission system on the basis of retaining the low-speed high-torque characteristic of the hydraulic transmission and self-adaptive speed ratio adjustment.At the same time,the capacity characteristics of the system are changed by the capacity regulating device to meet the different requirements of the capacity characteristics of the system with full power matching and partial power matching,so that the full power matching and partial power matching can achieve better matching results.In view of this new transmission structure,taking the wheel loader as the service object,combining with the derivation of basic characteristics and the analysis of working principle,this paper puts forward the selection method of hydraulic torque converter,the optimization design method of power matching,the optimization design method of gear transmission ratio and the design method of shift strategy,and preliminarily realizes the creation of the design theory of hydraulic reflux variable speed transmission system,which provides a reference for the design of the new transmission structure The hydraulic variable speed drive system with capacity regulating device can be used in engineering,agricultural and military vehicles.The main contents of this paper are as follows:(1)In view of the low transmission efficiency of the traditional hydraulic transmission system and the inability to balance full power matching and partial power matching,comprehensively considering the efficiency characteristics and matching characteristics of the hydraulic transmission system,a power reflux hydraulic transmission system with a capacity adjustment device is proposed,and the basic characteristics are deduced according to the working principle of this structure.According to the research results of basic characteristics,the influence of the penetration characteristics of the torque converter on the matching performance of the power reflux hydraulic transmission system is analyzed,and it is revealed what kind of penetration characteristics of the torque converter can ensure a good matching performance.On this basis,considering that the capacity adjustment device can change the working characteristics of the capacity coefficient of the power reflux hydraulic transmission system,a method for obtaining the value range of the capacity coefficient of the torque converter is proposed.The above research provides theoretical guidance for the structural design,basic characteristic analysis,and torque converter selection of power reflux hydraulic transmission system.(2)Calculated the speed ratio characteristic,torque ratio characteristic,capacity characteristic,and efficiency characteristic of the power reflux hydraulic transmission system under different structural parameters,and analyzed the influence of different structural parameters on the basic characteristics of the power reflux hydraulic transmission system.On this basis,combined with the working principle of the capacity adjustment device,careful consideration is given to the full power matching and partial power matching of the wheel loader.The key structural parameters are selected as design variables,and the optimization evaluation index is designed.A multi-objective optimization model is established,and the structural parameters of the planetary platoon and the speed ratio of the capacity adjustment device are optimized.Based on the above research,the power matching optimization design method of the power reflux hydraulic transmission system with capacity adjustment device is proposed,which provides theoretical guidance for power matching and structural parameter optimization design.(3)Aiming at the blindness of designing the transmission ratio according to the offset geometric series in the traditional speed ratio design method,data mining is carried out through the historical working conditions of the wheel loader,and the middle gear ratio of the gear transmission is optimized.Combining the two output characteristics of the power reflux hydraulic transmission system with capacity adjustment device and historical working condition data,the maximum transmission ratio and the minimum transmission ratio are designed.On the basis of determining the maximum and minimum gear ratios,a non-dominated sorting genetic algorithm with an elite strategy is selected.A multi-objective optimization solution for the mid-gear speed ratio of the gear transmission of the hydraulic reflux transmission system operating under the V-type operating condition is carried out.Because the capacity adjustment device has two-speed ratios,it is necessary to make a preliminary formulation of the speed ratio switching strategy of the capacity adjustment device when multi-objective optimization of the speed ratio of the gear transmission.Through cluster analysis of historical working condition data,combined with the working principle of the capacity adjustment device,the speed ratio switching strategy of the capacity adjustment device for the optimization design of the gear transmission ratio is designed.(4)In view of the complex and changeable working conditions of the engineering,agricultural and military vehicles,the application of the traditional shifting strategy to the capacity adjustment device will lead to frequent or wrong shifts.It is proposed to introduce a working condition recognition algorithm in the capacity adjustment device shifting strategy.The shifting strategy is revised according to the recognition results of the working conditions to avoid frequent shifts and wrong shifts.In view of the problem that the introduction of the operating condition recognition algorithm in the shifting strategy of the capacity adjustment device will reduce the real-time performance of the control system,in the design of the working condition recognition algorithm,the code complexity of the algorithm is reduced as much as possible on the basis of ensuring the realization of the functional requirements of the recognition algorithm.In view of the problem that the capacity adjustment device will change the speed ratio of the power reflux hydraulic transmission system before and after shifting,the same set of gear transmission shift strategy will reduce the performance of the wheel loader,corresponding to the two-speed ratios of capacity adjustment devices,two sets of gear shifting strategies are designed respectively.The above research puts forward the shift strategy including the capacity adjustment device and the shift strategy of the gear transmission,which provides theoretical guidance for the new structure of the shift control.(5)Build a hardware-in-the-loop verification platform and an experimental bench for the power reflux hydraulic transmission system,and carry out empirical research on the real-time performance of shift control strategies and system capacity characteristics.By building a hardware-in-the-loop verification platform,compiling the shift control strategy into the physical controller,the wheel loader model runs in the lower computer in real-time,and the real-time characteristic of the shift strategy is verified.By building an experimental bench for the power reflux hydraulic transmission system,the system capacity characteristics were obtained.Through comparison,the correctness of the method of solving the problem of the engineering,agricultural and military vehicles' s failure to balance full power matching and partial power matching was verified by comparison. |
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