| Bulldozer is a typical construction machine,which plays an important role in infrastructure such as earthwork and water conservancy projects.The working process of a bulldozer mainly consists of several parts: soil cutting,earth moving,soil unloading and backtracking.In the working process,it circulates back and forth,and each cycle is accompanied by severe fluctuation of load,so the working condition is extremely complex.The hydro-mechanical compound transmission not only has the characteristics of high efficiency and safety of the mechanical transmission,but also has the characteristics of the hydraulic transmission can be continuously variable to withstand the variable load,which is very suitable for the bulldozer with complex and changeable working conditions.However,the structure of the hydro-mechanical compound transmission is relatively complicated.The shift process needs the joint participation of the hydraulic and mechanical branches.The smoothness of the shift process has become an important reason to restrict the rapid promotion of the transmission.It is necessary to study the shifting smoothness of hydro-mechanical compound transmission.This thesis describes the basic principles of the hydro-mechanical composite transmission,and performs a detailed comparative analysis on the mode of flow diversion and flow confluence of the transmission.Through formula derivation and MATLAB software analysis,it is concluded that the transmission scheme of split moment and converging speed is more suitable for bulldozer.Finally,an equal-ratio continuous transmission scheme of the hydro-mechanical compound transmission was determined,and the power transmission path of the scheme was analyzed.According to the operating characteristics of wheeled bulldozers,kinematics and dynamics of wheel dozer are analyzed.With reference to the parameters of mainstream bulldozers at home and abroad and the transmission scheme of the hydro-mechanical compound transmission proposed in this thesis,the main parameters of the bulldozer are reasonably matched.Under the condition of constant ratio continuous transmission,thetransmission ratio parameters and component parameters of the hydro-mechanical compound transmission are analyzed and calculated.This thesis summarizes the evaluation indexes and methods of the shift smoothness of the hydro-mechanical compound transmission,and analyzes the main factors affecting the shift smoothness of the hydro-mechanical compound transmission.The method of adding hydraulic buffer valve in the clutch control oil circuit is put forward to reasonably control the pressure rise curve of the clutch in the process of shifting,and the working principle and structure of the hydraulic buffer valve are analyzed to improve the gear shifting smoothness.The simulation model of clutch control oil route and hydro-mechanical compound drive system is established by using AMESim,and the correctness of the model is verified.The effects of the main parameters of the hydraulic buffer valve on the clutch shift oil pressure are analyzed by simulation.The results show that: in order to make the clutch boost curve closer to the ideal boost curve,Main parameters for hydraulic buffering valve of shift clutch hydraulic impact has carried on the simulation analysis,the results show that: in order to make the clutch boost curve closer to the ideal boost curve,the stiffness of the compression valve compression spring should be set larger within a reasonable range.The stiffness of the valve return spring is as small as possible,and the size of the throttle orifice of the common oil circuit of the clutch oil pressure system should be selected about 2mm.Aiming at the main factors affecting the smoothness of the gear shifting process,the simulation is carried out to obtain the change rules of the speed and torque of the output shaft of the compound transmission during the gear shifting process.It was concluded that the fuel pressure of the clutch was selected to be smaller within a reasonable range.The clutch’s oil-filling flow rate is a little larger.The value of the hydraulic pump variable rate should be close to the theoretically calculated value 1 during shifting.Properly extending the overlap time of the clutch to be released and the clutch to be engaged can effectively improve the smoothness of the shifting process. |
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