变量齿轮同步分流器的设计及特性仿真

针对智能农业机械多执行机构同步动作、调速及变载荷恒速运动问题,提出一种变量齿轮同步分流器。分析了中心轮齿数和行星轮均布个数对同步状态的影响,得到各分流单元瞬时状态全部相同的工作条件是中心轮齿数能被行星轮均布个数整除,各分流单元瞬时同步。利用Fluent软件的动网格技术,对分流器流量特性进行非定常模拟,分析出不同中心轮齿数对平均流速和分流器体积的影响。研究了负载压力不变齿轮转速变化、负载压力变化齿轮转速不变、负载压力和齿轮转速均变化的工况下,瞬时流速和平均流速的变化规律。结果表明:行星轮和中心轮回转中心的连线与中心轮参与拟合轮齿的对称中心线重合误差为0.05?和0.1?时,6个出口瞬时流量误差分别为?0.56%和?1.12%;负载压力不变时,根据平均流速与齿轮转速的线性关系,通过伺服电机调节中心轮转速实现变量控制;负载压力变化时,伺服电机调节中心轮转速实现恒流控制,理论上实现了执行机构瞬时同步、调速或恒速动作,试验验证了恒流控制的可行性。

Design and characteristic simulation of variable gear synchronous shunt

Abstract: Modern intelligent agricultural machinery in the course of operation requires multiple actuators synchronous action. Commonly used hydraulic synchronous control methods are throttling speed control, dividing-collecting valve control, synchronous shunt control, and proportional servo valve control. In contrast, gear synchronous shunt has a low fault rate, stable performance, and the same size of the shunting units. It is easy to achieve multi-loop synchronous control. The structure of general gear shunt is tandem, which is difficult to guarantee the consistency of the gear phases in shunting units. The instantaneous flow rates of every shunting unit cannot be synchronized in the working process. When the load pressure is changed, the action speed of the hydraulic cylinder is changed using such a tandem gear shunt in hydraulic circuit, and the speed cannot be adjusted. Aiming at the problems mentioned above, a parallel variable gear synchronous shunt was proposed in this paper. The influence of center gear teeth number and uniformly distributed planetary gear numbers on synchronization status of the shunting units was analyzed. The working condition was the center gear teeth number that can be divided by uniformly distributed planetary gears number, from which shunting unit instantaneous states were all the same. By analyzing the gear meshing point position of a shunting unit, the instantaneous flow and theoretical displacement formulas of shunt outlet were deduced. The outlet instantaneous flow rate can be characterized by instantaneous flow velocity, and the outlet mean flow rate can be characterized by mean flow velocity. The instantaneous flow rate or instantaneous flow velocity of shunting units contained in the variable gear synchronous shunt were equal. Therefore, the instantaneous working statuses of every shunting unit were exactly the same, and the shunting units were instantaneously synchronized. Then the mean flow rate or the mean flow velocity equal conditions were naturally satisfied. The geometric models of different cases were created, and then the meshes of flow domains were divided properly using triangular unstructured meshes globally in the ICEM CFD module. Finally, the generated mesh files were imported into the Fluent module for simulation analysis. After the flow domain model parameters were set in the Fluent module, the transient flow characteristics of the shunt were simulated by using the dynamic mesh technique. The data files generated by Fluent module calculation were imported into the CFD-Post module for data post-processing. By setting up monitoring points at the center of outlets, variation law of flow velocity with time was gained. After analyzing influence of different center gear teeth number on the mean flow velocity and the shunt geometrical dimensions, an appropriate center gear teeth number was selected under the limits of shunt accuracy and shunt size. In order to get variation law of instantaneous flow velocity and main flow velocity, the shunt was studied in the following conditions: constant load pressure with a changing gear speed, a changing pressure with constant gear speed, and a concurrently changing load pressure and gear speed. The results showed that, when the coincidence errors of the two lines were 0.05° and 0.1°, the instantaneous shunt errors were ±0.56% and ±1.12%. When the load pressure was constant, variable control can be realized by adjusting the center gear rotational speed through a servo motor. When the load pressure was changed, constant flow control can be achieved by adjusting the center gear rotational speed also. A three-gear shunt test prototype was developed. In order to complete the constant flow control test, the test prototype was connected to the pump and motor dedicated test bench to build a test system. The experimental results of constant flow rate control verified the correctness and feasibility of simulation results. In this study, instantaneous synchronization, speed regulation or constant speed motion of the actuators can be realized theoretically, which provides a theoretical basis for the high precision synchronous control of the variable gear synchronous shunt on the intelligent agricultural machinery.