Jul 19, 2023
History of Rexroth axial piston pump (motor)
BOSCH REXROTH axial piston pump (motor) is one of the most widely used hydraulic components in modern hydraulic transmission. It is widely used in various hydraulic systems because it can easily realize variables and make the hydraulic system easy to realize power regulation and stepless speed change.

The embryonic form of axial piston pump (motor) can be traced back to the early 16th century. Ramelli developed a leather sealed axial piston pump for drawing water from the mine. From the perspective of structure, it is very similar to the current piston pump. Until 1905, American professor Harvey William and engineer Reynolds Janny designed the hydrostatic transmission device of the swashplate pump (motor) with end flow distribution, which was used in the hydraulic system of the turret steering of warships. Later, people called the pump with this structure Janny pump, and they introduced mineral oil into the transmission medium for the first time, which opened the prelude to the development of modern hydraulic technology.

In 1907, American Renault improved Janny pump plunger transmission machinery, effectively improving its operating efficiency.

Inclined shaft piston pump developed relatively late. In 1930, Professor Hans Thomas of Switzerland designed the first inclined shaft pump. Later generations often call the inclined shaft pump Thomas pump. The center line of its cylinder body forms an included angle with the center line of the transmission shaft, which reduces the overturning torque of the cylinder body to the port plate, so the allowable inclination angle is larger.

In the mid-1950s, Denison company of the United States and Lucas company of the United Kingdom got rid of the tradition of Janny pump and designed a swashplate pump with bearing supporting cylinder block. The transmission shaft of this kind of pump only transmits torque and does not transmit bending moment, which ensures the good contact of the flow distribution pair. With the improvement of manufacturing level, its working pressure is increased to 35MPa, and the speed is also greatly increased, causing a leap in the history of swashplate pump.

In the mid-1960s, due to the requirements for the integration of hydraulic system, especially the application in the closed circuit of walking vehicles, the through shaft pump obtained new development. Because the end of the main shaft can be equipped with auxiliary pumps or other pumps, the through shaft pump has the composite function of integrating multiple components, which greatly simplifies the hydraulic system, which is another leap in the development of swashplate pump (motor).

After the 1970s, many manufacturers of axial piston pumps (motors) in Europe and the United States gradually rose and made many technological innovations in different fields. For example, Vickers launched PVB light pump for the energy-saving requirements of injection molding machines; The combination of pump (motor) and electronic technology is becoming closer and closer, and a variety of control methods have emerged.

In 1966, China designed CY14-1 axial piston pump (motor) after integrating the characteristics of foreign swashplate piston pump. After more than 30 years of solid line, cy14.1 pump (motor) has been greatly improved four times. The first two times are mainly based on standardization and volume reduction, and it is improved to cy14-1a type; For the third time, CY14-1B pump (motor) was formed to solve the burning of oil distribution plate, wear of swashplate, and process problems; For the fourth time, q "cy14-1bk series open low-noise pumps and QT" cy14-1bk series through shaft pumps were developed in view of the defects of CY14-1B type, such as high noise, low speed, easy to loosen and take off boots, poor reliability, poor self-priming ability, incomplete specifications and no through shaft pumps.

After entering the 1990s, Bosch Rexroth company in Germany developed A4V pump. The plunger forms an intersection angle with the transmission shaft. When working, the centrifugal force is conducive to the return stroke of the plunger, and is also conducive to reducing the diameter of the valve plate and the linear speed of the valve distribution surface of the cylinder block; The use of spherical flow distribution is conducive to compensating the overturning torque of the cylinder block caused by axial eccentric load. This type of pump has been widely used in modern industrial fields. At present, almost all of the axial piston pumps used as variable displacement pumps and variable displacement motors are divided into inclined shaft and swash plate, which are described below respectively.

(1) Bent shaft or axial piston pump (motor) this is Hansthoma's 1940 invention. Then in 1946, he improved the synchronous drive of the cylinder block, changed the universal joint to the connecting rod mode, and changed the valve plate from flat to spherical. Recently, Bosch Rexroth has introduced an improved type of conical plunger (the plunger rod is installed on the sealing part), which integrates the connecting rod and the plunger. The invention has been continuously improved for more than 60 years since its inception and has now become the most widely used product in various fields.

At present, only Bosch Rexroth company produces variable bending shaft pumps. The main varieties are a7v series, with a displacement of 20~1000ml/r, a maximum pressure of 35MPa, and a variable angle of 18 °. The company also developed a7vo series pumps, which are conical connecting rod piston type, with a displacement of 28~1000ml/r and a maximum pressure of 40MPa.

On the basis of a7v and a7vo, Bosch Rexroth also developed a6v and a6vm variable motors. In addition, Linde company also produces bmv/r variable bending motor, but the maximum displacement is only 50.2~60.3ml/r, the rated pressure is 42MPa, and the maximum pressure is 50MPa, which is used for the closed circuit of small hydraulic equipment. At present, Beijing Huade Hydraulic Group Co., Ltd., Shanghai hydraulic pump factory, Guiyang 501 factory, etc. produce Bosch Rexroth bent shaft pumps and motors. The development trends of bent shaft pumps and motors are as follows.

1) Due to structural reasons, the bent shaft pump cannot be equipped with an auxiliary pump, so it can only be used as an open circuit pump; In addition, because the variable mechanism of the bending shaft pump drives the cylinder body to swing together, the response speed of the variable is low.

2) As a variable displacement pump, due to its complex manufacturing process and high cost, the variable displacement pump with a displacement of less than 250ml/r is gradually losing its competitive advantage, but the large displacement pump is still its own.

3) Both quantitative and variable motors, especially the conical connecting rod piston structure with a bending angle of 40 °, have a good development prospect because of its unique advantages of large starting and transmission torque.

(2) Swash plate axial piston pump and motor This is the result of the improvement of the axial hydraulic transmission device invented by Harvey Wiliams and Reynolds Janney in 1905. The variable displacement pump and variable displacement motor with simpler structure has been in mass production since 1950. Compared with the inclined shaft type, it has a small volume, lightweight, and good displacement control response performance, so it is increasingly used in various hydraulic pumps. Swashplate axial piston pump and motor can also be divided into light-duty and heavy-duty.

1) Light axial piston pump and motor. As early as the 1960s, some piston pump manufacturers attempted to develop a variable displacement piston pump with medium pressure (medium load), simple structure and low price, which can compete with gear pump and vane pump. In the early 1960s, British d0wty company designed a swashplate axial piston pump called "VADIS ´", which has a maximum pressure of 20MPa, simple structure, and uses many cutting and non cutting parts. There are only 8 kinds of parts that need machining, and its cost can even compete with gear pump. At the same time, Vickers of the United States also designed a PVB series light piston pump, which has a simple structure. The valve plate is connected with the rear cover. The cylinder block, slipper and other parts are made of cast iron or powder metallurgy. The single acting cylinder (spring return) is used to realize the variable. It is mainly used on machine tools, and was once used in emulsion medium as the pressure below 7MPa, but it did not attract people's attention at that time. It was not until the late 1970s that Daikin company of Japan developed V15 and v38 series light piston pumps (with displacement of 14.8ml/min and 37.7ml/min respectively, rated pressure of 14MPa and maximum pressure of 21MPa) on the basis of the introduction of 15 and 18 series pumps of Santander company of the United States that the light piston pump attracted the attention of the world.

The light piston pump of Daikin company of Japan has many structures similar to PVB pump. It also uses a single acting variable cylinder and uses a spring to reset the swashplate. In order to reduce the force of the return spring, in the design, the rotation center of the swashplate is higher than the intersection of the center line of the cylinder body and the center plane of the slipper ball head, so as to compress the center spring of the cylinder body and the liquid pressure in the plunger cylinder to reset the swashplate. Perhaps due to the friction pair materials and heat treatment, the valve plate is still installed between the cylinder body and the rear cover of Daikin's light piston pump.

The light piston pump developed by Daikin company of Japan has attracted extensive attention. At the 1981 Japan oil and air pressure exhibition, Japanese oil research, Xuanchang, Fengxing, bueryue and other companies have successively exhibited light piston pumps.

Around the 1990s, many manufacturers in the world successively developed light piston pumps, such as Sant é Trane, Eaton, Dennison and Parker in the United States, Bosch Rexroth in Germany, and ATOS in Italy. China introduced PVB light piston pump from the United States in 1983, and then Chongqing Hydraulic parts factory also introduced A10V light piston pump from Bosch Rexroth of Germany. However, due to the high price, it has not been widely promoted in the domestic market.

All light piston pumps are based on constant pressure variable displacement pumps. After the development of light piston pump, Daikin company of Japan first developed the load sensing variable pump and used it in injection molding machine to make the output power of the pump closest to the power required by the load. That is, when the pump is unloaded, the variable mechanism can return to zero automatically so that the no-load power consumption of the system can also be minimized.

2) Heavy duty swashplate pump and motor. Heavy duty swashplate pump and motor refer to the swashplate pump and motor with complex structure, which are used in severe working conditions, heavy load, rated pressure of 31.5~42mpa, maximum pressure of 40~50mpa.

① Swashplate pump and motor system for closed circuit. It is widely used in engineering and construction machinery. Its feature is that the pump is equipped with a makeup oil pump, and the pump and hydraulic motor are jointly equipped with a full set of integrated valves for the closed system. As long as users connect two pipelines, they can make the system operate, such as a vibratory roller, cement mixer, etc. this system is widely used. The first manufacturer of this product is Sauer, whose products are 20 series pumps and motor systems. In the mid-1980s, Shanghai high pressure oil pump factory introduced the American Sauer 20 series pump and motor system. Now, Sauer has jointly produced the latest 90 series pump and motor systems in Pudong, Shanghai.

At present, many companies in the world have produced this kind of pump and motor closed system. Among them, Eaton company and Denison company in the United States, Bosch Rexroth company and Linde company in Germany are more famous. Among them, American companies all closed systems of swashplate pump swashplate motor, German Bosch Rexroth company is closed system of swashplate pump bent shaft motor, while Linde company has both closed system of swashplate pump swashplate motor and closed system of swashplate pump bent shaft motor. Guizhou Liyuan Hydraulic parts factory also produces Sauer 20 series pump and motor closed system.

② Swashplate pump for open system. Generally, open system pumps have higher requirements than closed system pumps, requiring them to have better self-priming capacity, lower noise and more variable types, so closed system pumps generally cannot be used in open systems. However, in order to reduce costs and improve the generalization of pump parts, closed system pump manufacturers often derive open system pumps from closed system pumps. For example, the a4sv0 open system pump of Bosch Rexroth is developed from the A4V closed system pump; The hpr202 series open system pump of Linde company is an improved product of hpv202 closed system pump. CY type axial piston pump, which is widely produced in China, also belongs to open system heavy-duty swashplate pump.

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