Axial Piston Pump Overview of Principle and Classification
Posted on 18/04/2024
1. Principle
The number of plungers in an axial piston pump has a great influence on the flow pulsation. If the number of plungers is large, the flow pulsation is small. Using an odd number of plungers will result in smaller pulsations than using an even number of plungers. This pump is a high-pressure and ultra-high-pressure pump, and the pressure is generally 100~320 kgf/cm2. The structure is compact, the radial size is small, the moment of inertia is small, the volumetric efficiency is high, and it can work under high pressure and high speed conditions. The axial size is large, the structure is complex, manufacturing is difficult, and the price is high.
2. Classification
1) Straight-axis and inclined-axis styles: An axial piston pump whose drive shaft is consistent with the axis of the cylinder is called a straight-axis pump. It relies on the inclination angle of the transmission plate to adjust the flow rate, also called a swash plate type. An axial piston pump in which the drive shaft is tilted at a certain angle with the cylinder is called an oblique axis pump. It relies on the tilt angle of the cylinder to adjust the flow rate, also known as a swing cylinder type. The straight-axis type (swashplate type) has a simple, compact and efficient structure. It can be used at higher pressures and allows higher rotational speeds. However, the contact between the end of the plunger and the transmission swashplate is weak and it is not resistant to shock and vibration. ; Good oil absorption, but requires higher oil filtration precision. The oblique axis type (swing cylinder type) has good impact and vibration resistance, and the cylinder swing angle can reach 25°. It has lower requirements for oil filtration precision, but it has a complex structure and large external dimensions, and allows a lower speed at large flow rates.
2) Point contact type and slipper type refer to the contact method between the plunger and the transmission plate. The point contact type has a simple structure, but the contact stress is very large. It is generally used within 100 kgf/cm2 and is not suitable for higher pressures. The sliding shoe structure is more complex, but the contact stress is smaller.
3) Valve flow distribution and end face flow distribution Valve flow distribution means setting two one-way valves at the inlet and outlet of the pump. It has a simple structure and reliable sealing, but it has a large structure, poor self-priming ability, and affects the reversibility of the pump and motor. The end face distribution structure is simple, the range of pressure and speed is large, the self-priming ability is good, and it can automatically compensate after wear, but it requires high oil purity and does not affect the reversibility of the pump and motor.
4) Through-shaft type and non-through-shaft type. The through-shaft type means that the transmission shaft of the cylinder passes through the swash plate. Its bearings are at both ends of the transmission shaft, and the radial load is supported by the transmission shaft. The shaft diameter is larger, and the cylinder hole distribution circle diameter is also larger. The sliding speed of the sliding shoe is high, but it is light in weight, small in size, with few parts, and can be connected in series. Auxiliary hydraulic pump. The non-through-shaft transmission shaft does not pass through the swash plate, and the cylinder is mounted on the bearing of the pump body to limit the tilt of the cylinder and the shaft diameter is small.
5) Single hinge type, double hinge type and hingeless type. The single hinge type has large flow pulsation and is not suitable for high-speed rotation. The flow pulsation of the double-hinge type is smaller than that of the single-hinge type, and the speed can be increased. The hingeless structure has high strength and can withstand impact loads.
3. Flow calculation
Straight axis type (swash plate type) flow
Q=π/4·nd2zD0tgγ1 (cm3/min)
Inclined axis type (swing cylinder type) flow rate
Q=π/4·nd2zD0sinγ2 (cm3/min)
In the formula: Q——flow rate
n——Hydraulic pump speed (rev/min)
d——Plunger diameter (cm)
z——number of plungers
D0——Plunger distribution diameter (cm)
γ1——swash plate inclination angle
γ2——cylinder inclination angle
