The reliability of the hydraulic system is expressed by the fault free service time of the main engine hydraulic system under normal operation under rated working conditions. Obviously, the longer the trouble free service time, the better the reliability. The reliability of a main engine hydraulic system is not good, which is meaningless. The service life of the hydraulic system mainly depends on the following factors. The three factors are equally important in the whole machine. Any problem in any link will affect the normal operation of the whole machine.

（1）液压元件的设计；

(1) Design of hydraulic components;

（2）元件的选择；

(2) Selection of components;

（3）使用与维护。

(3) Use and maintenance.

小型自动上料搅拌车液压系统的优化

Optimization of hydraulic system of small automatic feeding mixer

1小型自动上料搅拌车液压系统故障原因分析

Failure analysis of hydraulic system of 1 small automatic feeding mixer

自动上料搅拌车在建设过程中的重要作用日益彰显。大型自动上料搅拌车一般从搅拌站装上搅拌好的混凝土，转运工地使用；而小型自动上料搅拌车一般是在工地附近，具有自装卸、配料与自搅拌功能，减少长距离运输且省工的特点。自动上料搅拌车的液压系统又分为闭式液压系统与开式液压系统。

Automatic loading mixer plays an increasingly important role in the construction process. Large automatic loading mixer truck generally loads the mixed concrete from the mixing plant and transports it to the construction site for use; The small automatic loading mixer is generally near the construction site, with the functions of self loading and unloading, batching and self mixing, reducing long-distance transportation and saving labor. The hydraulic system of automatic feeding mixer is divided into closed hydraulic system and open hydraulic system.

一客户的批量小型自动上料搅拌车在使用过程中出现以下几种故障现象：（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；（2）液压油散马达的进油胶管出现多台爆管故障；（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。

A customer's batch small automatic feeding mixer truck has the following faults during use: (1) under no-load, the rotating speed of the drum can meet the design requirements, but it is difficult to start after filling, and the rotating speed of the drum is very low even under high engine speed; (2) Several oil inlet hoses of hydraulic oil dispersion motor burst; (3) The failure rate of the drum motor is very high. Many motors are stuck inside or the shaft end seal is damaged, and oil is spilled outward.

从原理上来看，液压系统为开式负载敏开芯回路，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。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。

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, takes the pilot control valve as the main switch, and realizes the forward and reverse rotation of the can motor by controlling the rocker switch of the electromagnetic change-over valve. The oil return of the reversing valve is divided into two ways to return to the oil tank: one way returns to the oil tank through the throttle valve, and the other way drives the oil dispersion motor to dissipate heat for the oil return of other systems.

小型自动上料搅拌车液压系统的优化

Optimization of hydraulic system of small automatic feeding mixer

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。

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 valve port of the throttle valve, and the throttle valve port adjusts the speed of the oil dispersion motor according to the idle speed of the engine before leaving the factory. Once the throttle valve port is fixed, the oil passing capacity will be limited to a certain range, However, the output flow of the change-over valve is directly proportional to the engine speed. When the engine is running at high speed, the oil at the T port of the change-over valve cannot quickly return to the oil tank, resulting in too high pressure at the oil inlet pipe of the oil dispersion motor, which exceeds the pressure borne by the rubber hose, so pipe explosion occurs from time to time. Since it is impossible to obtain 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, check the system status and operating conditions of the real vehicle on site, and analyze the failure causes from the operating 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4m/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。

It can be seen from the pipeline situation on site that the oil suction pipe is too long and 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 large flow rate of hydraulic oil in the oil suction pipe of the gear pump reaches 4m / 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 accelerates wear, and the volumetric efficiency decreases rapidly, resulting in an obvious decrease in the speed of the drum under heavy load.

让客户现场演示真实工况，发现两个重要问题：

Let the customer demonstrate the real working conditions on site and find two important problems:

（1）转罐转速在停止时会发出一声尖叫，停止突然，尤其是在发动机大油门的情况下，驾驶员操纵翘板开关使转罐停止时没有任何缓冲；（2）在装料后转场的过程中，为了不让混凝土凝固，罐体会始终在转动状态。然而，罐体转速在行走过程中非常快，即缸体转速与发动机的转速成正比，当驾驶员加大油门高速行驶时，转罐转速也会随之加快，这是非常危险的事情，因为转罐较高，在急转弯时转罐在惯性作用下易出现翻车事故。

(1) When the rotating speed of the drum stops, it will emit a scream and stop suddenly. Especially when the engine is at high throttle, the driver operates the rocker switch to stop the drum without any buffer; (2) In the process of transfer after loading, the tank will always rotate in order to prevent the concrete from solidification. However, the speed of the tank body is very fast during walking, that is, the speed of the cylinder body is directly proportional to the speed of the engine. When the driver increases the accelerator to drive at high speed, the speed of the drum will also accelerate, which is a very dangerous thing, because the drum is high, and the drum is prone to rollover accident under the action of inertia during sharp turning.

由此得出系统还存在两个问题：（1）液压系统冲击严重，没有缓冲功能，且换向阀阀芯回中位速度不受控制，阀芯中位机能为O型，正在高速旋转的转罐实然间被停止，而罐体质量为7t，惯性很大，在停止时通过减速机直接作用在转罐马达上，使马达受力超过力矩，造成马达内部卡死或轴端密封损坏向减速机内部串油；（2）转罐转速不可控，转罐速度只与发动机的转速呈正比，当驾驶员快速行驶时，转罐速度随之加快，此现象完全不能满足工况的实际需求。

From this, it is concluded that there are two problems in the system: (1) the hydraulic system has serious impact and no buffer function, and the return median speed of the reversing valve spool is not controlled. The median function of the spool is O-type. The rotating drum rotating at high speed is actually stopped, while the mass of the tank is 7T and the inertia is very large. When it is stopped, it acts directly on the drum motor through the reducer, Make the force of the motor exceed the rated torque, resulting in the internal jamming of the motor or the damage of the shaft end seal, and oil spilling into the reducer; (2) The rotating speed of the can is uncontrollable, and the speed of the can is only proportional to the speed of the engine. When the driver drives fast, the speed of the can is accelerated, which can not meet the actual needs of the working conditions.

2自动上料搅拌车液压系统特改优化

Special modification and optimization of hydraulic system of 2 automatic feeding mixer

在现有系统的基础上进行特改，受到减速机、齿轮泵、换向阀及结构件等现有元器件布局的限制，同时成本也是客户关注的，所以在有限费用的前提下，通过原理及细节的调整优化系统，使其故障率降低到可接受的范围内。

The special modification based on the existing system is limited by the layout of existing components such as reducer, gear pump, directional valve and structural parts, and the cost is also concerned by customers. Therefore, on the premise of limited cost, the system is adjusted and optimized through principles and details to reduce the failure rate to an acceptable range.

（1）增加缓冲功能，在换向阀的A、B口安装两个二次压力补油阀，其压力设定为12.5MPa，稍高于系统工作压力，并具有补油功能，在换向阀阀芯关闭时，能够使马达在转罐惯性的作用下继续转动，压力油通过二次压力补油阀溢出到换向阀T口，同时马达的低油腔通过另一个补油阀完成补油，保护了转罐马达与减速机。

(1) The buffer function is added. Two secondary pressure oil makeup valves are installed at ports a and B of the change-over valve. The pressure is set to 12.5mpa, slightly higher than the system working pressure, and has the oil makeup function. When the change-over valve core is closed, the motor can continue to rotate under the inertia of the drum, and the pressure oil overflows to port t of the change-over valve through the secondary pressure oil makeup valve, At the same time, the low oil chamber of the motor completes oil replenishment through another oil replenishment valve to protect the drum motor and reducer.

（2）实现转罐速度可调。将现有的翘板开关控制换向阀先导油路改为具有摩擦定位功能的液控手柄控制换向阀换向，使转罐速度可调可控，且不增加驾驶员的劳动强度。当驾驶员驻车搅拌时，可将手柄推大，转罐转速随发动机转速变化；当行走时可将液控手柄调小角度位置，使换向阀的流量需求很小，在负载敏换向阀的共同作用下，不管发动机转速是多少，转罐即可在恒定的转速下运转，达到既不让混凝土凝固、又不会在行走过程中发生危险的目的。

(2) The speed of can transfer is adjustable. The pilot oil circuit of the existing rocker switch controlled directional valve is changed into a hydraulic control handle with friction positioning function to control the directional valve, so that the rotating tank speed can be adjusted and controlled without increasing the labor intensity of the driver. When the driver parks the car for mixing, push the handle to the large position, and the rotating speed of the drum changes with the engine speed; When walking, the hydraulic control handle can be adjusted to the small angle position, so that the flow demand of the directional valve is very small. Under the joint action of the load sensitive directional valve, no matter what the engine speed is, the drum can run at a constant speed, so as to achieve the purpose of neither allowing the concrete to solidify nor causing danger during walking.

（3）在换向阀的先导油口a、b处增加单向节流阀，使换向阀关闭时具有一定时间的延时，这样在转罐停止前有一段减速的过程，与二次压力缓冲阀共用，达到动作缓和与保护元件的效果。

(3) A one-way throttle valve is added at the pilot oil ports a and B of the directional valve to make the closing of the directional valve have a certain time delay. In this way, there is a deceleration process before the drum stops, which is shared with the secondary pressure buffer valve to achieve the effect of action relaxation and protection of components.

（4）更换已损坏的齿轮泵，并加粗吸油管径25mm、加大吸油滤油器过油能力，使吸油大流速控制在1m/s以下。

(4) Replace the damaged gear pump, increase the oil suction pipe diameter to 25mm, increase the oil passing capacity of the oil suction filter, and control the large oil suction flow rate below 1m / s.

（5）拆除换向阀回油管路上的节流阀，使换向阀回油直接回油箱，油散马达由另外一个泵单独驱动，使回油顺畅，避免回油压力过高导致液压元件故障及不必要的压力损失。

(5) Remove the throttle valve on the oil return pipeline of the change-over valve to make the return oil of the change-over valve return directly to the oil tank. The oil dispersion motor is driven separately by another pump to make the oil return smooth and avoid the failure of hydraulic components and unnecessary pressure loss caused by too high return oil pressure.