Requirements of Rexroth piston pumps for motors – Autosys

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Generally, in the hydraulic systems of fixed equipment, the hydraulic pumps are usually driven by electric motors. The Rexroth piston pump also belongs to the category of hydraulic systems for fixed equipment; so what are the requirements for the drive motor in a Rexroth piston pump? 　　First: Type. Since hydraulic pumps usually start under no-load conditions, there are no high requirements regarding the starting torque of the motor. The load variations are relatively gentle, and the number of starts is limited; therefore, Y-series squirrel-cage asynchronous motors can be used. However, if the hydraulic system has high power but the grid capacity is limited, a wound-rotor motor can be used. For hydraulic pumps that use frequency conversion to regulate flow, an AC asynchronous motor controlled by an inverter should be used to drive the hydraulic pump. 　　Depending on the operating environment of the hydraulic pump, different protection requirements are applied to its drive motor: in clean and dry environments, open-type motors (with protection rating IP11) are suitable for use; in relatively clean environments, protected motors (with protection ratings IP22 and IP23) are appropriate; in humid, dusty, high-temperature, corrosive, or exposed to wind and rain environments, enclosed motors (with protection rating IP44) should be used; in explosive hazard environments, explosion-proof motors (such as d2 IICT4) are necessary. 　　Second: Speed. The speed of the motor should be compatible with the speed of the hydraulic pump. A coupling is typically used to connect the electric motor to the hydraulic pump, and the speed of the electric motor should be within the optimal speed range of the hydraulic pump. Otherwise, it will reduce the efficiency of the hydraulic pump. 　　Motors of the same type with identical capacity (power) usually come in different speeds to choose from. Low-speed motors have a large number of pole pairs, are larger in size and weight, more expensive, and require pumps with a higher flow rate (at a constant volume flow); high-speed motors are the opposite. Therefore, the speed of the motor should be considered in conjunction with the pump’s flow rate, displacement, and other factors. 　　Third: Power. The power of the motor can be determined by referring to the drive power specified for the hydraulic pump in its product data sheet, assuming that the hydraulic pump is operating at its rated pressure and flow rate. If the hydraulic pump operates at other pressures and flow rates, the power of the motor can be calculated using the formula, allowing for the selection of a suitable motor. If the driving power of the hydraulic pump varies significantly, the power required for each operating stage should be calculated separately; thereafter, an average power Pcp is determined, which is then used to determine the driving power of the hydraulic pump. Since the motor can operate under overload for a short period of time, its power only needs to be greater than the average power calculated above, with the maximum power not exceeding 1.25 times the motor’s rated power. 　　The requirements for electric motors driving Rexroth piston pumps are generally as mentioned above; when purchasing or selecting a motor, these same three requirements are used as a guide for making the decision. Therefore, when selecting an electric drive for a Rexroth piston pump, we only need to consider the type of electric drive, its speed, and its power.