Created on:2021-06-10 13:55

Working principle of single acting radial piston motor

Working principle of single acting radial piston motor

As there are two main types of radial piston motors, namely single acting and multi acting, their working principles are introduced in the following.

(1) Working principle of single acting radial piston motor As shown in Figure o, five (or seven) cylinders are radially and evenly arranged along the circumference of the housing 1. The plunger 2 in the cylinder is connected with the connecting rod 3 through the ball hinge, and the end of the connecting rod contacts with the eccentric wheel of the crankshaft 4 (the center of the eccentric wheel is O1, the rotation center of the crankshaft is O, and the eccentricity of the two is e). One end of the crankshaft is the output shaft, and the other end is through the cross The coupling is connected with the valve distribution shaft 5. Two sides of the partition wall on the valve distribution shaft are oil inlet chamber and oil discharge chamber respectively.


After the high-pressure oil from the oil source enters into the oil inlet chamber of the motor, it is introduced into the corresponding piston cylinder (1), cylinder (2) and cylinder (3) through the slots (1), cylinder (2) and cylinder (3) of the housing. The hydraulic force P produced by the high pressure oil acts on the top of the plunger and is transmitted to the eccentric of the crankshaft through the connecting rod. For example, the force acting on the eccentric by the piston cylinder ② is n, and the direction of the force is along the center line of the connecting rod and points to the center O1 of the eccentric. The force n can be divided into normal force FF (the line of action coincides with the connecting line 001) and tangential force F. The tangential force F produces a torque to the rotation center 0 of the crankshaft, which makes the crankshaft rotate counterclockwise around the center line 0. The piston cylinder (1) and (3) are similar to this, except that their position relative to the spindle is different, so the torque generated is different from that of cylinder (2). The total torque of crankshaft rotation is equal to the sum of the torque generated by the piston cylinder connected with the high-pressure chamber (①, ② and ③ in the case of figure o). When the crankshaft rotates, the volumes of cylinders ①, ② and ③ increase, while the volumes of cylinders ④ and ⑤ decrease, and the oil is discharged through the oil passage of the shell ④ and ⑤ through the oil discharge chamber of the port shaft 5.

When the valve distribution shaft and crankshaft rotate synchronously for an angle, the "partition wall" of the valve distribution shaft closes the oil passage (3). At this time, the cylinder (3) is not connected with the high and low pressure chambers. Cylinders (1) and (2) are supplied with high pressure oil, which makes the motor produce torque, and cylinders (4) and (5) discharge oil. As the valve distribution shaft rotates with the crankshaft, the oil inlet chamber and the oil discharge chamber are respectively connected with each plunger in turn, so as to ensure the continuous rotation of the crankshaft. In one revolution, each plunger reciprocates the oil in and out once. The working principle of other single acting motors is similar to this.

The working principle of single acting radial piston motor should pay attention to the following points.

① The motor can be reversed by changing the inlet and outlet of the motor. If the eccentric ring is separated from the output shaft of the motor and measures are taken to make the eccentric distance adjustable, the purpose of changing the displacement of the motor can be achieved, and the variable displacement motor is made.

② The motor shown in Figure o is shell fixed, so it is also called shaft motor; if the crankshaft is fixed, it can be made into shell motor. The shell motor is especially suitable for installation in the winch drum or on the wheel hub of the vehicle to directly drive the wheel and become the wheel motor.


③ The motor shown in Figure o of distribution pair is axial distribution. Because one side of the valve shaft is a high-pressure cavity and the other side is a low-pressure cavity, the working process of the valve shaft is subject to a large radial force, which pushes the valve shaft to one side and increases the gap on the other side, resulting in the wear of the sliding surface and the increase of leakage, resulting in the decrease of efficiency. For this reason, it is often adopted to set up a symmetrical balancing oil groove to balance the radial force. As shown in Figure P, the static pressure balance valve distribution shaft is sealed by a sealing ring. The central C-C window hole is the valve distribution window hole, the annular grooves on B-B and D-D are the oil inlet and oil return window holes respectively, and A-A and E-E are the static pressure balance semicircular annular grooves. It is assumed that the sealing rings are respectively placed in the center of the sealing belt. If the direction of oil inlet and outlet is as shown by the arrow in Figure P, the holes marked with the symbol P are high-pressure chambers, and the holes marked with the symbol T are low-pressure chambers. It can be seen that the circumferential pressures of B-B and D-D are the same, and there is no radial force; the upper chamber of C-C window hole section is connected with the oil inlet, which is the high pressure side, and the lower chamber is connected with the oil return port, which is the low pressure side, so the valve distribution shaft is subject to great radial force. In order to balance the radial force, semicircular annular balancing oil grooves A-A and E-E are set at both ends of the valve distribution shaft to make the upper cavity filled with high pressure oil. In order to reduce leakage, sealing rings are set between the cavities. In order to ensure the static pressure balance of the upper and lower sides, the relevant dimensions of the oil distribution window and the balance oil groove should meet the following equation:

a+e=2(b+c) (5-4)

Where a -- width of flow distribution window;

B -- width of sealing belt of balance oil tank;

C -- width of balance oil tank;

E -- the width of the sealing belt of the flow distribution window.

Because the radial force is balanced, the friction force is very small, which improves the mechanical efficiency. At the same time, the radial clearance between the valve shaft and the valve sleeve is reduced, the leakage is reduced, and the volumetric efficiency is improved. In the normal working range, the total efficiency is between 85% and 90%.

Figure Q shows the end face flow distribution structure of the crankshaft connecting rod hydraulic motor. The crankshaft 13 drives the port plate 4 and the pressure plate 2 to rotate synchronously through the square head 12, and the port is realized during the rotation. During start-up or no-load operation, the backup spring (disc spring) 3 makes the valve plate and pressure plate close to the cylinder block 11 and the end cover. The design ensures that the close force is greater than the separation force between the valve plate and the cylinder block, and the hydraulic pressure realizes the close force during operation. However, due to the non coincidence of separation force and sticking force, the valve plate has tilting moment. By using the static pressure balance structure design, the end face port pair can achieve complete balance in theory.


It should be pointed out that in order to improve the reliability and performance of the hydraulic motor and make its structure more compact, one of the development trends at home and abroad is to use the end port pair.

④ In addition to the port pair, the performance of the crankshaft connecting rod hydraulic motor largely depends on the connecting rod motion pair. The typical structure of connecting rod ball joint pair is shown in Figure R. It consists of two pairs of friction pairs, the ball head of connecting rod 4 and the ball socket of plunger 2, the bottom of connecting rod slider 5 and crankshaft (eccentric wheel) 6. The metal contact between the bottom of the connecting rod slider and the crankshaft (eccentric wheel) was in the early stage, and the wear-resistant alloy was cast at the bottom of the slider to reduce the friction. Some motor crankshafts (eccentric wheels) are equipped with roller bearings, which use rolling friction to replace the sliding friction between the bottom of the slider and the eccentric wheel; at present, most motors are designed as hydrostatic balance or hydrostatic support. An oil chamber is set at the bottom of the slider, and the pressure oil enters the bottom oil chamber through the damper in the center of the connecting rod. The sliding block doesn't float during the operation, the liquid pressure in the oil chamber balances most of the plunger thrust, and the friction pair is well lubricated.


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