Automatic concrete mixer plays an increasingly important role in the construction process. Large mixer truck generally loads the mixed concrete from the mixing station and transports it to the construction site for use; while small mixer truck is usually near the construction site, which has the functions of self loading and unloading, batching and self mixing, reducing long-distance transportation and saving labor. The hydraulic system of automatic concrete mixer is divided into closed hydraulic system and open hydraulic system. A customer's batch of small automatic concrete mixer in the process of using the following fault phenomenon:

 

自动混凝土搅拌机液压系统故障原因分析

Failure analysis of hydraulic system of automatic concrete mixer

( 1) 空载下，转罐转速可达到设计要求，而装满料以后很难起动，即使在发动机大转速下转罐转速也很低;

The results are as follows: (1) under no-load condition, the rotating speed of the drum can meet the design requirements, but it is difficult to start when the drum is full, even at high engine speed;

( 2) 液压油散马达的进油胶管出现多台爆管故障；

(2) the oil inlet hose of hydraulic oil dispersion motor has multiple tube burst faults;

( 3) 转罐马达的故障率非常高，多台出现马达内部卡死或轴端密封损坏向外串油。

(3) the failure rate of the rotary drum motor is very high, many motors are stuck inside or the shaft end seal is damaged, and the oil flows outward.

从原理上来看，液压系统为开式负载敏感开芯回路，通过安装在发动机上的齿轮泵持续向换向阀供油，由先导控制阀作为总开关，通过控制电磁换向阀的翘板开关实现转罐马达的正转与反转。

In principle, the hydraulic system is an open load sensitive open core circuit, which continuously supplies oil to the change-over valve through the gear pump installed on the engine. The pilot control valve is used as the main switch, and the forward and reverse rotation of the can motor is realized by controlling the rocker switch of the electromagnetic change-over valve.

换向阀的回油分两路回油箱: 一路通过节流阀回油箱，另一路驱动油散马达，为其他系统的回油进行散热。通过故障情况与原理对比分析，认为换向阀的回油通过节流阀的阀口来控制油散马达的工作转速，且节流阀阀口是在出厂前根据发动机怠速调节油散马达转速的，一旦节流阀阀口固定，通油能力就会被限制在一定的范围内，然而换向阀的输出流量与发动机的转速成正比关系，在发动机高速运转时，换向阀 T口油液无法快速回到油箱，造成油散马达的进油管处

The return oil of the reversing valve is divided into two ways: one is returned to the oil tank through the throttle valve, and the other is driven by the oil dispersion motor to dissipate heat for the return oil of other systems. Through the comparative analysis of fault conditions and principles, it is considered that the return oil of the directional valve controls the working speed of the oil dispersion motor through the orifice of the throttle valve, and the throttle valve orifice regulates the speed of the oil dispersion motor according to the engine idle speed before leaving the factory. Once the throttle valve orifice is fixed, the oil flow capacity will be limited in a certain range, but the output flow of the directional valve is proportional to the engine speed When the engine is running at high speed, the oil at the T port of the directional valve can not return to the oil tank quickly, resulting in the oil dispersion at the oil inlet pipe of the motor

压力过高，超过胶管承受的压力，所以爆管现象时有发生。因无法得到更详细的技术参数与资料，重载转速慢及马达故障率高是否有直接关联，通过现场查看实车的系统现状及使用过程工况，从使用工况来分析故障原因。

The pressure is too high, which exceeds the pressure of the hose, so the tube explosion occurs from time to time. Because we can't get more detailed technical parameters and data, whether there is a direct correlation between the slow speed of heavy load and the high failure rate of motor, through the on-site inspection of the status quo of the real vehicle system and the working conditions of the use process, we can analyze the fault causes from the working conditions.

从现场的管路情况看到，吸油管过长过细，且齿轮泵的位置高于油箱吸油口的位置，经理论计算齿轮泵吸油管液压油大流速达到 4 m / s，远超过设计标准。同时，齿轮泵本身的自吸能力差，在高转速时吸油管内产生负压，齿轮泵内部吸油不足加速磨损，容积效率快速下降，导致转罐在重载情况下转速下降明显。

From the field pipeline situation, it can be seen that the oil suction pipe is too long and too thin, and the position of the gear pump is higher than that of the oil suction port of the oil tank. Through theoretical calculation, the high flow rate of the hydraulic oil in the oil suction pipe of the gear pump reaches 4 m / s, far exceeding the design standard. At the same time, the self-priming capacity of the gear pump itself is poor, resulting in negative pressure in the oil suction pipe at high speed, insufficient oil suction in the gear pump, accelerated wear, and rapid decline in volumetric efficiency, which leads to obvious decline in the rotating speed of the drum under heavy load.