Main parameters and common problems of hydraulic pump
Main parameters and common problems of hydraulic pump
1.6.11 installation flange and shaft extension dimension series
The installation flange of hydraulic pump includes diamond, square, polygon (including circle), cylindrical shaft extension, 1:10 conical shaft extension with external thread and involute spline with 30 ° pressure angle. In order to facilitate the design, manufacture and maintenance, the above installation flange and shaft extension dimensions have been serialized and standardized. In GB / T 2353-2005 "hydraulic pump and hydraulic motor mounting flange and shaft extension dimension series and marking code", the pump and motor mounting flange and shaft extension dimension series and marking method are specified.
1.6.12 driving mode and requirements for prime mover
Fixed equipment hydraulic system, the hydraulic pump is usually driven by electric motor. The hydraulic system of walking machinery mostly uses internal combustion engine to drive hydraulic pump.
(1) Requirements for motors
① Because the hydraulic pump is usually started under no-load, the starting torque of the motor is not too high, the load change is relatively stable, and the starting times are not many, so the Y Series cage type asynchronous motor can be used. When the power of the hydraulic system is large and the capacity of the power grid is small, the wound rotor motor can be used. For the hydraulic pump with variable frequency flow regulation scheme, AC asynchronous motor controlled by frequency converter should be used to drive the hydraulic pump.
The working environment of the hydraulic pump is different, and the protection type requirements for its driving motor are different: open motor (protection mark is ipi1) should be used in clean and dry environment; protective motor (protection mark is IP22 and IP23) should be used in clean environment; closed motor should be used in humid, dusty, high temperature, corrosive or wind and rain prone environment In explosive environment, explosion-proof motor (such as D Ⅱ cT4) should be used.
② The speed of the motor should match the speed of the hydraulic pump. The coupling is usually used between the motor and the hydraulic pump, and the speed of the motor should be within the best speed range of the hydraulic pump. Otherwise, the efficiency of the hydraulic pump will be reduced.
The same type of motor with the same capacity (power) usually has different speed for selection. Low speed motor has many pole pairs, large size and weight, high price, and requires a larger pump displacement (in the case of a certain flow); high speed motor is the opposite. Therefore, the speed of the motor should be considered together with the flow and displacement of the pump.
③ Power of motor
a. When the hydraulic pump works under the rated pressure and flow, the power of the motor can be selected according to the driving power of the hydraulic pump in the hydraulic pump product sample.
b. If the hydraulic pump works under other pressure and flow, the power of the motor can be calculated by equation (1-18), and the appropriate motor can be selected.
Where △ P -- the pressure difference between the inlet and outlet of the hydraulic pump (when the inlet pressure of the pump is close to zero, the outlet working pressure P of the pump can be used to replace △ P), MPa;
Q -- quantity of hydraulic pump, L / min;
η - total efficiency of hydraulic pump,%.
c. If the driving power of the hydraulic pump changes greatly, the required power of each working stage should be calculated respectively, and then the average power PCP should be calculated according to equation (1-19), and then the driving power of the hydraulic pump should be determined. Since the motor can be overloaded in a short time, the power of the motor should be greater than the average power calculated above, and the maximum power should not be greater than 1.25 times of the rated power of the motor.
Where PI -- power required in the i-th working stage of each working cycle, kW;
Ti -- the duration of the t working stage, S.
d. For the fast and slow alternating circulation system with oil supplied by double pumps, which is often used in engineering, the driving power of fast and slow working stages should be calculated respectively. The first pump should be able to bear higher load (pressure × flow) than the second pump; the total load of the multi pump should not exceed the torque that the shaft extension of the pump can bear.
(2) When the hydraulic pump is driven by the internal combustion engine, there are two different situations: one is that the hydraulic pump is only a part of the driving load of the internal combustion engine; the other is that all the power of the internal combustion engine is used to drive the hydraulic pump.
① When the hydraulic pump is only a part of the driving load of the internal combustion engine, the power of the internal combustion engine is large, which can always meet the required power of the hydraulic pump. The speed of internal combustion engine should match the best speed of hydraulic pump. High speed internal combustion engine usually has a deceleration device to make the hydraulic pump work in the best speed range.
② The system that all power of internal combustion engine is used to drive hydraulic pump is called full hydraulic drive system. The full hydraulic drive system of vehicle and walking machinery usually adopts the volume speed regulation system of variable pump or variable motor to meet the requirements of large speed change of walking machinery. The maximum speed of the internal combustion engine shall meet the maximum flow required by the system and shall not exceed the maximum allowable speed of the hydraulic pump. If the speed of the internal combustion engine is too high, a reduction device should be set. The maximum power of internal combustion engine should be slightly higher than that required by hydraulic system.