Created on:2021-06-07 11:17

Working principle of axial piston pump

Working principle of axial piston pump

⑥ The reciprocating movement of the plunger in the cylinder bore is the basis for the plunger pump to change the working volume of the seal, absorb and press oil. The function of the return mechanism is to ensure that the end face of the sliding shoe is close to the inclined plane of the swash plate at any time without separation. There are some methods for plunger return, such as using auxiliary pump to supply oil to make plunger return, dispersing spring return, centralizing center spring return and constant clearance forced return.

The auxiliary pump supplies oil to the oil suction port of the main pump to ensure that the working chamber has a certain pressure in the oil suction condition, so as to overcome the friction force, inertia force and so on and make the plunger extend. In order to make the main pump not empty, the flow of the feed pump is generally 10% ~ 15% larger than that of the main pump, and the excess oil is returned to the oil tank through the relief valve. In order to reduce energy loss and system heating, the oil supply pressure should not be too high, generally set at about 0.5MPa. This kind of return way is reliable, but the hydraulic system is complex and accompanied by energy loss, so it is generally not used alone.

The plunger of point contact pump is extended (returned) by springs distributed at the bottom of each plunger, and retracted by swash plate, so the self-priming ability is poor, and the spring is easy to cause fatigue damage due to high frequency operation, so this kind of structure has been rarely used. Generally, the axial piston pump adopts the center spring return mechanism shown in Fig. J. the spring force of the center spring 1 drives the sliding shoes and the plunger return through the sleeve, steel ball or ball hinge, and return disc, while the swash plate forces it to retract, which has strong self-priming ability. Moreover, in this structure, the spring bears static load, and its compression does not change with the rotation of the pump driving shaft, so the spring will not produce fatigue damage. At present, this structure is widely used in axial piston pump.

J.jpg

⑦ The main function of the valve plate is to make the working volume cavity composed of plunger and cylinder bore connect with the oil suction cavity when its volume increases, and connect with the oil discharge cavity when its volume decreases. As shown in Figure K (a), port P1 is the oil suction window, port P2 is the oil pressure window, and the waist shaped hole indicated by the dotted line is the oil passage at the bottom of the cylinder block. When the plunger extends outward from the cylinder bore, the working chamber increases and absorbs oil from the oil suction window through the oil passage; when the passage is between the oil suction and oil discharge grooves, the working chamber is not connected with the oil pressure window and the oil suction window; when the plunger retracts inward, the working chamber decreases and the oil is pressed to the oil discharge window through the passage.

K.jpg

In order to ensure the sealing, the interval angle of the oil suction and pressure windows of the valve plate should be equal to or slightly greater than the corresponding center angle of the waist hole at the bottom of the cylinder block. When the plunger deviates from the top and bottom dead center position, the reciprocating motion of the plunger in the cylinder bore will change the volume of T. If the interval angle of the oil suction and pressure windows of the valve plate is larger than the enveloping angle of the waist shaped hole at the bottom of the cylinder block, the phenomenon of oil trapping will occur in the △ φ region, resulting in pressure shock [Fig. K (a)] and noise when the bottom cavity of the plunger is suddenly connected with the oil suction and pressure windows.

The measure to alleviate the phenomenon of trapped oil is to set the unloading and damping groove (also known as triangular eyebrow groove) as shown in Figure K (b) at the end of the port window. In order to reduce the hydraulic impact, the working chamber of the plunger is not immediately connected with the oil drain groove after leaving the oil suction groove. The oil in the working chamber is pre compressed by the trapped oil phenomenon, and then connected with the oil drain window. Using the same method, the plunger working chamber can be pre depressurized during the transition from oil drain window to oil suction window. The hydraulic shock can be greatly improved by setting the damping groove.

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