| Popis: |
The Republic of Vietnam has great mineral resources. Open pit mines use hydraulic excavators. In hot climate, the excavators lose capacity, and the number of the hydraulics failures grows. To identify the causes of unstable operation of the hydraulics, the authors analyze the capacity reduction factors, namely, hydraulic pump leaks. The test subject is pump HPV95 for Komatsu hydraulic excavators. The axial-piston pump leaks take place in clearances of control and injection gears, and only have mutable and cyclic behavior in the piston and cylinder clearances. This has an adverse effect on uniformity of the pump flow and on stability of the injection pressure. Generally, leaks can be evaluated from the Reynolds equation of fluid flow rate in the ring clearance. The input data are the design variables of axial-piston pump HPV95 and power fluid temperature range of Komatsu hydraulic mining excavators operated in open pit mining in the south in the Republic of Vietnam. Matlab-based Simulink modeling shows that with increasing temperature of power fluid, leaks in the injection gear grow nonlinearly in the absolute value and so does the surging amplitude in the pump flow. As a consequence, the pressure fluctuations and vibrations in the hydraulic gear elevate. The modeling also exhibits higher surge and reduced net capacity of the hydraulics with rising temperature of power fluid. These changes are caused by reduction in the flow friction in the ring channel between the piston and block of cylinders. Thus, the power fluid cooling system engineering subject to hydraulics capacity, operating conditions and cooling methods is highly critical for the efficient operation of hydraulic mining excavators. |
