Research On Failure Analysis And Improvement Of Hydraulic Drive Fan System

With the stricter requirements of national energy conservation and emission regulation,the heat dissipation problem of construction machinery has been paid more and more attention.The traditional engine directly driven fan cooling system does not have the function of speed regulation.When the machine is at high speed,medium or low load and the temperature of coolant is low,the fan speed is high,causing the coolant to be over cooled.When the machine is under low speed and high load,the low fan speed cannot provide enough cool air volume so that the cooling system will be overheated.Therefore,the application of the traditional fan system is increasingly restricted.After the introduction of the temperature control unit and ECU in the hydraulically driven fan cooling system,the system control is more intelligent.Through the feedback of the temperature sensor and the ECU information processing,the temperature signal can be converted into an input signal for controlling the hydraulic flow or pressure.The disadvantages of the mechanically driven fan are avoided,and the component installation is relatively flexible.Therefore,the hydraulically driven fan cooling system will be more and more widely used in construction machinery,buses,railway tractors,heavy cargo transportation vehicles and other diesel-driven vehicles.In this paper,the issue that fan speed is decreased abnormally in the hydraulic drive fan system of a motor grader is taken as the start point.The theoretical analysis and the actual test are combined to find the root cause of this issue.The current system does not introduce a temperature control unit,it simply relies on pressure control to change fan speed,and the original design is upgraded to achieve intelligent control.The main work is as follows:Firstly,collect test data of this issue on machine,and investigate on this issue,analyze it from pressure and flow perspective.Establish failure mode analysis and confirm the root cause of this issue based on the required tests.Secondly,by introducing the electro-hydraulic proportional relief valve and formulating a new control logic,it is improved to a hydraulic driven fan system with temperature control function on the basis of the original design.In summary,infinite speed variation of the fan speed in the hydraulic driven fan system can be achieved through the good match of the cooling fan speed and the heat dissipation.