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According to the operation characteristics of high clearance self-propelled sprayer, an independent vertical shaft air suspension system with auxiliary chamber was designed. On the basis of the damping characteristic analysis and experiment of the air suspension with auxiliary chamber, the sprayer suspension control strategy was developed. Aiming at strong non-linearity and hysteresis for air suspension with auxiliary chamber, and when the sprayer performed road transportation and spraying operation, there was a contradiction between ride comfort and road friendliness, a hybrid sliding mode control method for sprayer chassis suspension based on skyhook reference sliding mode and ground-hook reference sliding mode was proposed. Finally, Matlab/Simulink was used to analyse the effect of the control method in different mixing coefficients. The simulation results showed that according to the requirements of different working conditions of the sprayer, by properly selecting the mixing coefficient γ value, the hybrid sliding mode control could simultaneously take into account the sprayer ride comfort and road friendliness, which was important to improve the sprayer overall performance and operating efficiency. 摘要 针对喷雾机特殊的作业特点和要求,设计了一种带附加气室的独立式立轴空气悬架系统,并在前期对带 附加气室空气悬架阻尼特性分析与实验的基础上,制定了喷雾机悬架的基本控制策略。然后针对带附加气室空 气悬架具有较强非线性和滞后性,且喷雾机道路转场运输和喷雾作业时,存在行驶平顺性和道路友好性之间矛 盾的问题,提出了一种基于天棚参考滑模和地棚参考滑模的悬架混合滑模控制方法。最后应用 Matlab/Simulink 对不同混合系数下的控制效果进行了分析。仿真结果表明,根据喷雾机不同工况要求,合理 地选择γ值,混合滑模控制可以同时兼顾喷雾机行驶平顺性和道路友好性,对提高喷雾机整机性能和作业效率 具有重要意义。 INTRODUCTION Large scale high clearance self-propelled sprayer plays a very important role in promoting food security production. However, because of the complex working conditions and unique working characteristics of the spray machine, special suspension system is needed to meet its requirements of high ground clearance, large vibration reduction stroke, convenient for four-wheel steering and wheelbase adjustment. In terms of how to reduce the dynamic load of the sprayer tire, improve the its spraying quality and ride comfort, the sprayer designers have proposed a variety of beneficial measures. For example, the designed sprayer is equipped with low-pressure, large-ground-area vacuum meridian cultivator tires, and adopts an independent chassis air suspension or hydropneumatic suspension with less unsprung mass and good nonlinearity (Wu X H et al., 2018). John Deere (Carlson B C et al., 2011; Wubben T M et al., 2007), AGCO (Slawson J, 2013; Steffensen C et al., 2012), HAGIE (Schaffer J A, 2002), AgriFac (Blaauw D, 1999; Ehlen V and Voth R, 2011) and other sprayer companies have applied for patents on air suspension, and their newly produced sprayers are also equipped with independent air suspension system. However, due to structural and spatial limitations, the independent air suspension system has not been equipped with damper, and only relies on the damping of tires and springs to attenuate the vibration (Chen Y et al., 2016; 2020). When the sprayer is running at a high speed or on the rough road conditions, the suspension vibration reduction effect will be Vol. 61, No. 2 / 2020 INMATEH – 116 greatly affected. Therefore, in order to better adapt to the sprayer complex working conditions, the design of the new sprayer chassis suspension system is imminent. In recent years, air suspension with auxiliary chamber, which uses air damping to reduce vibration, has gradually gained the attention of scholars (Liu H and Lee J C, 2011). Compared with traditional air suspension, air suspension with auxiliary chamber has the advantages of less heat, low manufacturing and maintenance cost (Quaglia G et al., 2012), better vibration reduction effect for the most sensitive frequency segment of human body (4~8Hz) (Todkar R G, 2011), which has been widely used in vibration reduction of commercial vehicles (Kat C J and Els P S, 2009; Porumamilla H et al., 2008) and rail vehicles (Docquier N et al., 2007). The introduction of auxiliary chamber into the sprayer's independent air suspension system can solve the problem that the suspension cannot be equipped with a damper due to structural and space constraints. Research scholars have carried out a lot of simulation and experimental research on the air suspension with auxiliary chamber structure (Quaglia G and Sorli M, 2001; Vogel J M and Kelkar A G, 2013), mathematical model (Wang J, 2012), dynamic characteristics (Nieto A J et al., 2008; Toyofuku K et al., 1999), control methods (Robinson W D et al., 2012; 2013) and so on. Currently, there are mainly three control forms for air suspension with auxiliary chamber. One is to adjust the stiffness of the suspension by switching the auxiliary chamber with different volumes. For example, Li Z X (2015) applied decision control method to control the adjustable volume of the air suspension with auxiliary chamber. In this way, the suspension needed to be equipped with an adjustable shock absorber so that the suspension relative damping coefficient could be adjusted when the system stiffness changed, so as to re-matched the suspension parameters. Another method is to change the damping ratio of the system by adjusting the opening diameter of the throttle valve. Such as the research of Porumamilla H. (2007) and Robinson W D et al. (2012). The sliding mode variable structure control and linear quadratic optimal control were used to control the air spring seat suspension with auxiliary chamber. This method needed to select a suitable variable throttle valve diameter to make the system air damping have good switching performance, and to ensure that the suspension stiffness and the natural frequency changed less during the change of the system damping ratio. Another control method is to adjust the auxiliary chamber volume and the variable throttle valve diameter. For example, Jerald M V et al. (2013) designed a device for continuous adjustment of auxiliary chamber volume and variable throttle valve diameter. Due to the complex structure and the large number of changing parameters of the suspension system, this control method is rarely studied. Based on this, according to the special operating characteristics and requirements of the sprayer, an independent vertical axis air suspension system with auxiliary chamber was designed. On the basis of the damping characteristic analysis and experiment of the air suspension with auxiliary chamber, the sprayer suspension control strategy was developed. Aiming at strong non-linearity and hysteresis for air suspension with auxiliary chamber, and traditional passive suspension could not take into account both road friendliness and ride comfort, a hybrid sliding mode control method for sprayer chassis suspension based on skyhook reference sliding mode and ground-hook reference sliding mode was proposed. Finally, Matlab/Simulink was used to analyse the effect of the control method in different mixing coefficients. MATERIALS AND METHODS Suspension structure design and vibration reduction strategy formulation ⚫ Suspension structure design The sprayer operation condition is complicated, so it not only needs to complete the transportation operation on the ordinary road, but also needs to complete the plant protection operation in the field. Two different working conditions have different requirements for suspension vibration reduction. During sprayer transportation operation, the sprayer speed is high (generally 20–40 km/h), the road conditions are good. The driver's riding comfort and the sprayer operation stability are the performance indexes that should be given priority to. Meanwhile, due to the sprayer large mass, the road friendliness should be taken into account to reduce the impact and damage to the road surface. During sprayer plant protection operation, the tire’s dynamic load should be minimized to prevent soil compaction and damage. In addition, although the sprayer speed is low (less than 20 km/h) during plant protection operation, due to the complicated road conditions in the field and the wide width of the boom, the slight tilt and vibration of the sprayer body will cause the boom to vibrate, swing and rotate, which greatly reduces Spray effect. Therefore, the sprayer ride comfort is also an important index to be considered during the its plant protection operation. In accordance with the special operating characteristics and requirements of the sprayer, based on the existing suspension Vol. 61, No. 2 / 2020 INMATEH – 117 system, an independent vertical axis air suspension system with auxiliary chamber was designed, and its structural assembly wad shown in Fig.1. In the process of suspension vibration reduction, the vibration caused by the road surface is first transmitted to wheel 1, and then transmitted to motor protection housing welding 3, and then reaches to vertical shaft 6. Guided by the internal shaft sleeve of Beam support column welding 7, the vibration through spring bottom support welding 21, air spring 10, spring top support welding 17, guide post 19, steering arm welding 15, positioning ring 14, and beam 9 in order. Finally, the vibration is transmitted to the sprayer body. Air spring 10, variable throttle valve 18, compressed air hose 11 and auxiliary chamber 12 form the suspension damping adjustment device. According to the driving conditions of the sprayer, by adjusting the opening degree of the variable throttle valve, the suspension damping is changed, and the impact load transmitted from the ground to the vehicle body is more effectively absorbed to ensure the ride comfort of the driver. 1 2 3 4 5 6 7 8 9 10 11

RESEARCH ON DESIGN AND HYBRID SLIDING MODE CONTROL OF HIGH CLEARANCE SELF-PROPELLED SPRAYER CHASSIS AIR SUSPENSION