Axial piston pump

Created on 2025.03.06

Axial piston pump

The piston pump driven by power machinery and the piston motor driven by pressure oil have the highest structural complexity and manufacturing cost among all kinds of hydraulic pumps and motors. Different from gear pump and gear motor, vane pump and vane motor, plunger pump and plunger motor's squeezer is plunger, and relies on the plunger to move back and forth in the special cylinder body to absorb or press and discharge liquid. The shell only contains, connects and supports various working parts, which is a kind of non pressure bearing hydraulic element. According to the position relationship between plunger and transmission shaft, plunger pump and plunger motor are divided into axial plunger type and radial plunger type. Here the axial piston pump and axial piston motor are introduced and discussed.

The center line of the plunger of the axial piston pump is parallel or nearly parallel to the axis of the cylinder block.

4.1.1 type characteristics

(l) Classification

Figure a shows the classification of axial piston pump. Among them, the movement direction of the plunger is parallel to the axis of the transmission shaft of the straight axis axial piston pump, which is also known as swash plate plunger pump because it changes the working volume of the piston hole cavity in the cylinder block to absorb and press oil and output hydraulic energy due to the reciprocating movement of the swash plate pushing or pushing the plunger backward. This kind of pump has two forms of through shaft and non through shaft, and their working principles are the same. However, the former's transmission shaft runs through the swash plate and its two ends are supported by bearings (generally rolling bearings), so it can be made into both cylinder rotary pump and swash plate rotary pump; the latter's transmission shaft does not run through the swash plate, one end (input end) of the transmission shaft is supported by bearings, and the other end is supported by the spline hole of the cylinder supported on the bearings.

The movement direction of the plunger intersects with the transmission shaft, and the angle is not more than 45 degrees. From the appearance, it is inclined or curved, so it is also called curved shaft plunger pump.

In addition to the fixed displacement pump, the straight axis and inclined axis axial piston pumps can be made into variable displacement pumps. Due to the variety of variable control mode, control purpose and control information, the axial piston pump is quite rich.

Among all kinds of piston pumps, the most widely used are the rotary cylinder type straight shaft pump with end face distribution and the inclined shaft pump with end face distribution.

(2) The characteristics are shown in the table below.

Characteristics of axial piston pump

type	Main advantages	Main disadvantages
Straight axis (swash plate) axial piston pump	① With reversibility, it can be used as both pump and motor ② It can realize the change of flow and direction by the swing of swash plate ③ High pressure, the pressure can reach 50MPa; large displacement, the displacement is usually 500ml / R, some as high as 1400ml / R ④ The response time can reach 0.2S ⑤ The efficiency is high, the volumetric efficiency is more than 95%, and the total efficiency is more than 90% ⑥ Small noise of inclined shaft pump ⑦ Through shaft pump can be combined with valve, and multiple pumps can be connected in series ⑧ Simple structure, small volume and high power density	① Generally, the structure is more complex than gear pump, vane pump and vane pump ② The ability of anti pollution is poor ③ The non TongZhou pump adopts large bearing supporting cylinder structure, which has large shape and noise, and can not be connected in series, so its application range is affected
Inclined axial piston pump	① The lateral force of plunger is smaller than that of straight shaft pump, so the friction loss is smaller ② The angle between the transmission shaft and the cylinder block is larger than that of the straight shaft pump. Generally, the angle between the inclined shaft pump and the cylinder block is 25 ° and the maximum is 40 ° for the inclined shaft pump. The angle between the straight shaft pump and the cylinder block is more than 90% ③ The transmission shaft does not need to pass through the valve plate, so the diameter of the spherical valve plate is smaller. Under the same working pressure, the specific power value [PV] of the friction pair is smaller, so the speed is higher ④ The self-priming ability of inclined shaft pump is better than that of straight shaft pump ⑤ Because there is a large sealing gap between the spherical surface of cylinder block and the spherical surface of valve plate, it is not sensitive to oil pollution ⑥ The moment of inertia of the rotating parts is small, so it has good starting characteristics and high starting efficiency ⑦ Variable, because of the large dip angle, so the variable range is large ⑧ The radial thrust ball bearing with large cone angle can bear both radial force and larger axial force, so it has long service life	① Because of the large swing angle, the two-way variable displacement pump needs larger swing space, so the inclined shaft pump with two-way variable displacement is larger and bulky than the straight shaft pump with two-way variable displacement ② It is difficult to make a double pump because it is not possible to use a through transmission shaft or two shafts connected. ③ The friction pairs in the structure, such as the match between the spindle ball socket and the connecting rod ball head and the match between the connecting rod small ball head and the inner ball socket of the plunger, are all spherical matches, and the processing accuracy is high, so the processability is poor.

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