Key points of axial piston pump

Created on 05.17

Key points of axial piston pump

(l) The application field cooperation is a kind of non pressure bearing hydraulic element with shell. The axial piston pump has the advantages of high pressure resistance, high efficiency, large transmission power, wide speed range, long service life and good bidirectional variable ability. Its disadvantages are strict requirements on the cleanliness of working medium, large flow pulsation and noise, complex structure, high price and difficult maintenance. In modern hydraulic engineering, axial piston pump is mainly used as the hydraulic pump in medium and high pressure (light series and medium series pump, the maximum pressure is 16 ~ 35MPa) and high pressure (heavy series pump, the maximum pressure is 40 ~ 56mpa) systems. Plunger pump is generally used as a "main pump" to transmit a certain power. Because of its high price, it is rarely used as an auxiliary oil source only for the purpose of controlling pressure or replenishing oil.

The straight axis axial piston pump has high allowable working pressure and speed, excellent variable performance, compact structure and high power density. It can be more convenient to install all kinds of auxiliary pumps or form double or multiple pump groups. Therefore, it can be widely used in engineering, agricultural machinery, lifting transportation and other walking machinery and various vehicles. Especially in the "hydrostatic drive" device which uses closed oil system and needs two-way variable displacement pump, through shaft swash plate pump occupies the vast majority of the market. The pump is also widely used in navigation, aviation, aerospace and other high-tech fields and military products. In the fixed installation of T industry production equipment, the straight shaft axial piston pump is mainly used for the hydraulic oil source of various materials pressure processing machinery and metallurgical machinery and other equipment which need higher working pressure.

In the field of walking machinery, in the past, the closed oil system used to use two-way variable inclined shaft axial piston pump, but because of its heavy structure and high price, it is more and more replaced by through shaft piston pump with better cost performance in the open hydraulic system including large and medium-sized hydraulic excavators. In the field of industrial equipment that needs high pressure and high power hydraulic system, the use of inclined shaft pump is larger than that of straight shaft pump. In addition to the industry habit, the advantages of compact one-way variable inclined shaft pump, such as stronger self-priming capacity and longer service life, are also important reasons.

In the common hydraulic system with mineral based hydraulic oil as working medium, the radial piston pump with clearance sealing port pair is increasingly replaced by the straight or inclined axial piston pump due to the effect of market rules. The traditional application field of seat valve type axial piston pump is all kinds of high pressure and ultra-high pressure hydraulic tools (such as all kinds of presses, material testing machines, steel prestressed tensioning machines, jacks, riveters, cutting pliers and all kinds of hydraulic tools, etc.). Another important use of them is in mining, metallurgy, chemical industry and other equipment that need to use Refractory working fluid. In recent years, this kind of pump is widely used in automobile hydraulic power steering system and hydraulic suspension system of some agricultural tractors, many of which use its control of oil absorption to achieve variable special performance.

(2) Parameter selection and type selection

① The rated pressure of the pressure axial piston pump should be greater than the working pressure of the main engine system, but it is allowed to use the maximum pressure occasionally in an instant or a short time. The rated pressure of the same plunger pump is different with different working medium and different rotating speed. The appropriate pump should be selected according to the working medium, rotating speed and working pressure of the system.

② The displacement of the pump is determined according to the speed requirements of the main engine. When selecting, the no-load displacement and the effective displacement of the pump should be known. At the same time, the long-term use efficiency will be reduced, which is generally 5%;

③ The maximum speed should not be used at the same time with the maximum pressure. The rotation speed of axial piston pump and motor shall be selected in strict accordance with the data specified in the product technical specification table, and shall not exceed the maximum rotation speed; the minimum rotation speed is not strictly limited under normal use conditions, but the minimum rotation speed shall not be less than 50R / min in some occasions requiring high uniformity and stability of rotation speed.

④ Driving power quantitative axial piston pump can be selected according to the method of gear pump and vane pump. For variable displacement piston pump, its driving power is related to variable mode and flow pressure characteristic curve. At this time, it should be selected according to the instructions.

⑤ The oil pressure in the shell of the oil discharge pressure pump depends on the maximum allowable pressure of the shaft seal, and the provisions of the product manual should be strictly followed. Too high oil pressure in the shell will lead to the early damage of the shaft seal.

⑥ The noise should be within the noise control value of the main engine. Low noise pump is suitable for indoor use.

⑦ Service life and price should consider the service life of the pump (the sum of pump operation time under rated conditions in overhaul period) and price factors. Generally, the overhaul period of vehicle pump and motor is more than 2000 hours, and that of indoor pump is more than 5000 hours. Generally, the price of straight axis axial piston pump (motor) is lower than that of inclined axis axial piston pump (motor), and the price of constant displacement pump is lower than that of variable displacement pump. Compared with other pumps, piston pump is more expensive than vane pump and gear pump, but its performance and service life are better than them.

⑧ When selecting the structure of the pump, the change degree of the flow demand of the main engine, the characteristics of the main engine, the circulation mode of the hydraulic circuit, the number of oil sources and the change degree of the speed of the prime mover should be considered.

There are two types of constant displacement pump and variable displacement pump: constant displacement pump has simple structure and low price, which is adopted by most main engine hydraulic systems; variable displacement pump has high energy utilization rate, which plays a role in more and more occasions. Generally speaking, if the power is less than 10kW, the working cycle is switch type, the pump can be completely unloaded when not in use, and the main engine has no fixed or little change in the oil supply flow under most working conditions, the quantitative pump can be considered; if the hydraulic power is greater than 10kw, the flow changes frequently and greatly, the variable displacement pump can be considered. If it is between the two, we should choose from the power loss and variable pump cost, oil temperature control and other factors.

The variable mode of variable displacement pump can be selected according to the characteristics of main engine and system, working condition requirements, control mode and other factors. If the pressure holding time accounts for a large proportion in the working cycle, constant pressure control is appropriate.

When the main engine system adopts the open circuit, the swing angle of the swash plate of the variable displacement pump or the swing angle between the transmission shaft and the cylinder block can only swing in one direction (γ = 0 → γ Max or γ = γ Max → 0), so the self-priming performance of the pump is high. If it is a closed loop, the swing angle of the variable displacement pump should be bidirectional (γ = - γ Max → + γ Max or γ = + γ Max → - γ max), and the auxiliary pump, integrated one-way valve, auxiliary pump safety valve, etc. should be connected in series on the variable displacement pump. Some of the high pressure relief valves are integrated into the motor, and some are integrated into the pump, so it is appropriate to select the same series of hydraulic transmission device.

When two different oil sources are used in the main engine system at the same time, it is better to use double pumps in series when possible, especially on mobile devices.

If the variable displacement pump is driven by internal combustion engine, the variable speed range is large, the angular acceleration is large, and the torque vibration is large.

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