The mechanical efficiency of the motor is equal to the ratio of the actual output torque to the theoretical torque in its operating state. The empirical formula for the mechanical efficiency of the variable motor is as follows: In the above formulas, is the laminar flow leakage coefficient, is the inlet and outlet pressure difference, is the oil dynamic viscosity, is the pump speed, is the motor speed, is the displacement ratio, is the laminar flow resistance coefficient , Is the mechanical resistance coefficient, is a certain torque loss that has nothing to do with the inlet and outlet pressure difference and speed, and is the full displacement of the pump. Obviously, it decreases with the increase of oil viscosity and speed, and increases with the increase of load pressure difference. The total efficiency of the closed hydraulic system increases with the increase of pressure; the total efficiency of the closed hydraulic system increases with the increase of the displacement ratio; with the increase of the displacement of the motor, the driving speed decreases, and the efficiency is obviously improved. The most severe working condition of the full hydraulic motor grader is a high-speed sports car. At this time, the efficiency of the closed system is low, and the system will generate a lot of heat. Whether the cooling system can meet the requirements of the sports car will directly affect the reliability and life of the hydraulic system. Closed system cooling calculation The closed system heat dissipation power loss power caused by the total efficiency of the closed pump and motor is the heat dissipation power required by the closed system.
When the efficiency of the closed system is low when the high-speed sports car is working, the theoretical formula for heat generation is inferred as follows, where is the flow of the system, is the heating power, and the heat balance of the closed system is calculated. The heat of the closed system is mainly fed into the system through the charge pump The cold oil replaces the hot oil and takes away. If the surface heat dissipation of the system components and the pipe loss are not taken into account, the heat absorbed per unit time when the cooling oil added to the system and the hot oil in the system reach a thermal balance is the heat dissipation power of the system. Assuming that the temperature difference between the cold oil added in the system and the hot oil in the system is (unit:), the heat absorbed by the cold oil added per second is the heat dissipation power of the system, namely: where:? Hydraulic oil density, take? The flow rate, the specific heat of the hydraulic oil, the difference between the oil temperature in the closed system and the oil tank temperature is proportional to the working pressure of the system. For a given closed system, its fuel supply and total efficiency are basically unchanged within the normal working range. Therefore, the difference between the oil temperature and the tank temperature in the system mainly depends on the working pressure of the system, that is, the load of the system.
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