Created on:2021-06-04 14:06

Working principle of axial piston pump 1

Working principle of axial piston pump 1

 

(l) The working principle and key points of the straight axis axial piston pump are shown in Fig. B. in the straight axis axial piston pump (through shaft structure), the plunger 3 is installed in the evenly distributed plunger holes in the cylinder block 4, and the head of the plunger 3 is installed with the slipper 2. Due to the return mechanism (not shown in the figure), the bottom of the slipper is always close to the surface of the swash plate 1. The swash plate surface has an inclination angle γ relative to the cylinder block plane (A-A plane). When the transmission shaft 6 drives the plunger to rotate through the cylinder block, the plunger makes a linear reciprocating motion in the plunger hole. In order to make the movement of the plunger and the switch between the oil suction path and the oil pressure path achieve accurate coordination, a fixed port plate 50 is placed between the port end face of the cylinder block and the oil suction channel and the oil pressure channel of the pump, and two arc channels (waist shaped port windows) are opened on the port plate. The front face of the valve plate is closely connected with the end face of the cylinder block, and it slides relatively; while on the back face of the valve plate, the two waist shaped valve windows should be respectively connected with the oil suction circuit and the oil pressure circuit of the pump.

When the cylinder block rotates in the direction shown in Fig. B, the plunger starts to extend from the top dead center (corresponding to the 0 ° position) within the range of 0 ° to 180 ° and the volume of the plunger cavity increases continuously until the bottom dead center (corresponding to the 180 ° position). In this process, the plunger cavity is just connected with the oil suction window of valve plate 5, and the oil is continuously sucked into the plunger cavity, which is the oil suction process. With the continuous rotation of the cylinder block, within the range of 180 ° to 360 °, the plunger starts to retract from the bottom dead center under the constraint of the swashplate, and the volume of the plunger cavity decreases continuously until the top dead center. In this process, the plunger cavity is just connected with the oil pressure window of the port plate 5, and the oil is discharged through the oil pressure window, which is the oil pressure process. Every revolution of the cylinder block, each plunger carries out half cycle oil suction and half cycle oil pressure. If the piston pump is driven by the prime mover and rotates continuously, it can continuously absorb and pressure oil.

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On the working principle of straight shaft axial piston pump, the following points should be noted.

① Variable problem Because the inclination angle between the swash plate and cylinder axis is γ, and the displacement of the pump is related to the inclination angle, when the inclination angle of the swash plate is not adjustable, it can be made into a quantitative pump. When the inclination angle of the swash plate is adjustable, it can change the length of the plunger stroke, thus changing the displacement of the pump, that is, to make a variable displacement pump, and change the direction of the inclination angle of the swash plate, it can change the direction of oil suction and pressure, that is, it becomes a two-way pump The variable pump.

The external dimension and support form of swash plate directly affect the external dimension and weight of variable displacement pump. There are two typical structures of swash plate: trunnion type and bracket type: the reaction force R1 of the trunnion of the former [Fig. C (a)] is far away from the action point of the resultant force F of the plunger assembly. In order to have enough rigidity and strength, the swash plate size has to be increased, so the space occupied by swash plate during swing is increased; the distance between the reaction force R1 of the trunnion of the latter [Fig. C (b)] and the resultant force F of the plunger assembly can be designed to be very small In recent years, the problem of swash plate stiffness basically does not exist, at the same time, the shape is also reduced, so the space occupied during swing is reduced, greatly reducing the weight of the pump.

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② There are three pairs of typical friction pairs in friction pair axial piston pump: plunger head and swash plate; plunger and cylinder bore; port plate and cylinder face. As the key parts of these friction pairs are in the high relative speed and high contact pressure friction conditions, the friction and wear directly affect the volumetric efficiency, mechanical efficiency, working pressure and service life of the pump.

③ The contact form of plunger and swash plate there are two kinds of contact form between plunger head and swash plate of straight axis axial piston pump: point contact and face contact. The structure of the ball head point contact axial piston pump is simple, but when the pump is working, the contact point between the piston head and swash plate is subject to great extrusion pressure. For example, when the diameter of the plunger d = 20 mm, the inclination angle of the swash plate γ = 20 ° and the working pressure P = 32 MPa, the extrusion force produced by the plunger head can reach f = 10.7 kn. In order to reduce the extrusion force, the piston diameter D and the pump working pressure P must be limited, so the point contact axial piston pump can not be used in high pressure and large flow situation. For this reason, the surface contact piston pump appeared and was widely used in most swash plate axial piston pump products.

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As shown in Figure D, the surface contact plunger pump is usually equipped with slipper (also known as slipper) 2 on the ball head of plunger 6, and the pressure oil in the cylinder hole can pass through the small hole between plunger and slipper to the slipper oil chamber, forming a hydrostatic thrust support between the contact plane of slipper and swash plate, which makes the lubrication surface contact between plunger and swash plate, thus greatly reducing the wear between plunger and swash plate And the friction loss, so that the working pressure of the pump increased significantly. But its structure is also complex. As shown in Figure D, most of the ball and socket slippers and plunger ball heads are hinged by rolling and ball wrapping process. In addition, there is a connecting rod slipper [Fig. e (a)], which is basically the same as the ball socket slipper, but the ball head is made on slipper 1 to make the column insert deeper into the cylinder bore, so as to improve the strength and anti pollution ability of the connecting part. Several concentric grooves 3 are made on the support plane at one end of the swash plate to form an auxiliary support surface, so as to reduce the contact specific pressure; FIG. e (b) shows a preloading device It can avoid large pollutants entering into the joint surface of ball hinge in the initial state (such as shutdown), and improve the anti pollution ability.

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