Hydraulic circuit for an injection system of an injection molding machine

Abstract

This invention relates to the technical field of hydraulic control for injection molding machines, and specifically discloses a hydraulic circuit for an injection system of an injection molding machine, including an oil tank, an injection cylinder, a power oil circuit with a first accumulator, and an injection oil circuit. The injection cylinder has an injection chamber and an injection retraction chamber. The injection oil circuit includes a first cartridge valve installed on one side of the injection chamber and a second cartridge valve installed on one side of the injection retraction chamber. The first cartridge valve is a three-position three-way proportional servo cartridge valve, with its first port connected to the first accumulator, its second port connected to the injection chamber, and its third port connected to the oil tank. The three-position three-way proportional servo cartridge valve has a conducting position that allows the second port to connect to either the first or the third port, and a closing position that cuts off the first, second, and third ports from each other. Utilizing its three-way and adjustable opening size characteristics, the injection system integrates three major functions: injection speed control, holding pressure control, and pre-plasticizing back pressure control, thus saving costs.

Description

Technical Field

[0001] This invention relates to the technical field of hydraulic control for injection molding machines, and specifically to a hydraulic circuit for an injection system of an injection molding machine. Background Technology

[0002] The high-speed injection process of injection molding machines usually requires extremely high speed and pressure. Therefore, modern large or precision injection molding machines often use accumulators as power sources to release a large amount of high-pressure oil in an instant to meet the injection requirements.

[0003] In existing technologies, injection systems generally employ two technical solutions: 1. An accumulator + spool servo valve solution is available, but the spool servo valve has a limited flow rate, which cannot meet the needs of high flow rate applications. If an ultra-large diameter spool servo valve is used, its step and frequency response data are not ideal, and the accuracy of high-speed injection cannot be guaranteed. 2. The accumulator + 3 two-way cartridge servo valves solution uses 3 servo valves to control injection speed, injection pressure and back pressure. However, its oil circuit is relatively complex and the cost of using 3 servo valves is high. Summary of the Invention

[0004] This invention addresses the aforementioned problems and aims to provide a hydraulic circuit for an injection molding machine system to solve the issues of slow response, low precision, and high cost in existing injection molding machine systems.

[0005] To achieve the above objectives, the present invention provides a hydraulic circuit for an injection molding machine injection system, including an oil tank, an injection cylinder, a power oil circuit, and an injection oil circuit, wherein the injection cylinder has an injection chamber and an injection retraction chamber; wherein, The power oil circuit includes a first accumulator; The injection circuit includes a first cartridge valve and a second cartridge valve. The first cartridge valve is configured as a three-position three-way proportional servo cartridge valve. The three-position three-way proportional servo cartridge valve has a first port that is fluidly connected to the first accumulator, a second port that is fluidly connected to the injection chamber, and a third port that is fluidly connected to the oil tank. The three-position three-way proportional servo cartridge valve has a conducting position that allows the second port to be fluidly connected to either the first port or the third port, and a closing position that cuts off the first port, the second port, and the third port from each other. The second cartridge valve has a first working port and a second working port. The first working port is in fluid communication with the oil line between the first accumulator and the first port, and the second working port is in fluid communication with the ejection chamber.

[0006] According to the hydraulic circuit of the injection system of the injection molding machine described above, the injection cylinder is further provided with a first pressure sensor, a second pressure sensor and a position ruler. The first pressure sensor is configured to detect the pressure of the injection chamber, the second pressure sensor is configured to detect the pressure of the ejection chamber, and the position ruler is configured to detect the displacement of the piston rod of the injection cylinder. The three-position three-way proportional servo cartridge valve is equipped with a valve clip for controlling the valve core opening. The valve clip is electrically connected to the first pressure sensor, the second pressure sensor, and the position ruler.

[0007] According to the above-described hydraulic circuit of the injection system of an injection molding machine, the three-position three-way proportional servo cartridge valve is provided with an external control oil port. A first pilot oil circuit is provided between the external control oil port and the first accumulator. The first pilot oil circuit includes a first check valve and an oil filter. The oil inlet of the first check valve is in fluid communication with the first accumulator, and the oil outlet of the first check valve is in fluid communication with the external control oil port through the oil filter.

[0008] According to the hydraulic circuit of the injection system of the injection molding machine described above, the power oil circuit further includes a third cartridge valve, the third cartridge valve having a third working oil port and a fourth working oil port, the third working oil port being in fluid communication with both the first oil port and the first working oil port, and the fourth working oil port being in fluid communication with the first accumulator.

[0009] According to the above-described hydraulic circuit of an injection system for an injection molding machine, the third cartridge valve is provided with a first pilot chamber, and a second pilot oil passage is provided between the first pilot chamber and the third working oil port and the fourth working oil port; The second pilot oil circuit includes a first shuttle valve, a first solenoid directional valve, and a second solenoid directional valve. The two inlets of the first shuttle valve are in fluid communication with the third working port and the fourth working port, respectively. The outlet of the first shuttle valve can be in fluid communication with the first pilot chamber via the first solenoid directional valve and the second solenoid directional valve.

[0010] According to the hydraulic circuit of the injection system of the injection molding machine described above, the first electromagnetic directional valve is provided with a first oil inlet, a second oil inlet, a first oil outlet and a first electromagnet, the second electromagnetic directional valve is provided with a third oil inlet, a first variable oil port and a second oil outlet, the oil outlet of the first shuttle valve is fluidly connected to the first oil inlet, the fourth working oil port is fluidly connected to the second oil inlet, the first oil outlet is fluidly connected to the third oil inlet, the first variable oil port is fluidly connected to the first pilot chamber, and the second oil outlet is fluidly connected to the oil tank.

[0011] According to the above-described hydraulic circuit of the injection system of an injection molding machine, the first electromagnetic reversing valve is also provided with a first electromagnet. When the first electromagnet is energized, the first oil inlet and the first oil outlet are in fluid communication. When the first electromagnet is de-energized, the second oil inlet and the first oil outlet are in fluid communication. The second electromagnetic reversing valve is also equipped with a second electromagnet. When the second electromagnet is energized, the first variable oil port is in fluid communication with the second oil outlet. When the second electromagnet is de-energized, the third oil inlet is in fluid communication with the first variable oil port.

[0012] The hydraulic circuit of the injection system of the injection molding machine described above further includes a pump group oil circuit, which includes a system oil port and a second check valve. The system oil port is in fluid communication with the third working oil port through the second check valve. The second check valve is configured to open from the system oil port toward the third working oil port.

[0013] According to the hydraulic circuit of the injection system of the injection molding machine described above, the second cartridge valve is further provided with a second pilot chamber, and a third pilot oil passage is provided between the second pilot chamber and the first working oil port and the second working oil port. The third pilot oil circuit includes a second shuttle valve and a third solenoid directional valve. The two inlets of the second shuttle valve are in fluid communication with the first working oil port and the second working oil port, respectively. The outlet of the second shuttle valve can be in fluid communication with the second pilot chamber through the third solenoid directional valve.

[0014] According to the hydraulic circuit of the injection system of the injection molding machine described above, the injection oil circuit further includes a replenishing check valve, which is arranged between the oil tank and the injection chamber and configured with its opening facing the injection chamber.

[0015] The present invention has the following beneficial effects: 1. A three-position three-way proportional servo cartridge valve is used as the main control element of the injection cylinder injection chamber. While saving costs, it integrates three major functions: injection speed control, holding pressure control, and pre-plasticizing back pressure control. The entire injection system meets the requirements of high pressure, high speed, high frequency response, and high precision. 2. During the injection action, the oil in the ejection chamber can enter the injection chamber through the second cartridge valve and the first cartridge valve, thereby realizing differential injection, reducing energy consumption and increasing injection speed. 3. The injection cylinder is equipped with a first pressure sensor, a second pressure sensor, and a position gauge. The three-position three-way proportional servo cartridge valve is equipped with a valve clasp for controlling its opening size. The valve clasp can receive electrical signals from multiple sensors, thereby realizing closed-loop control of the opening size of all actions and ensuring its high-precision operation. 4. By controlling the second pilot oil circuit, multiple functional modules of the accumulator can be switched, such as allowing only charging, stopping charging, and discharging and storing energy simultaneously, which can meet the needs under different working conditions and ensure the safety performance of the accumulator. 5. An oil replenishment check valve is installed on one side of the injection chamber. During the material storage action and back pressure control process, the oil tank can be used to replenish the oil in the injection chamber to ensure that the injection chamber does not suck in air during the material storage action and back pressure control. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall oil circuit of the injection system in an embodiment.

[0017] In the picture: 100. Fuel tank; 200, Injection cylinder; 210, Injection chamber; 220, Retraction chamber; 230, First pressure sensor; 240, Second pressure sensor; 250, Position ruler; 300. Power oil circuit; 310. First accumulator; 320. Third cartridge valve; 321. First shuttle valve; 322. First solenoid directional valve; 322a. First electromagnet; 323. Second solenoid directional valve; 323a. Second electromagnet; 400. Injection oil circuit; 410. First cartridge valve; 411. First check valve; 412. Oil filter; 420. Second cartridge valve; 421. Second shuttle valve; 422. Third solenoid directional valve; 430. Replenishment check valve; 500, Pump unit oil circuit; 510, System oil port; 520, Second check valve. Detailed Implementation

[0018] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the invention is not limited to these embodiments.

[0019] like Figure 1 As shown, in this embodiment, a hydraulic circuit for an injection system of an injection molding machine is provided, including an oil tank 100, an injection cylinder 200, a power oil circuit 300, an injection oil circuit 400, and a pump set oil circuit 500.

[0020] The injection cylinder 200 is the execution unit. The injection cylinder 200 has an injection chamber 210 and a retraction chamber 220. Hydraulic oil is introduced into the injection chamber 210 to drive the piston rod to extend, thereby performing injection or pressure holding actions. Hydraulic oil is introduced into the retraction chamber 220 to drive the piston rod to retract, thereby performing retraction actions.

[0021] The power oil circuit 300 includes a first accumulator 310, which can store hydraulic oil and provide power oil to the injection cylinder 200 during its operation, while the pump set oil circuit 500 is used to provide hydraulic oil to the first accumulator 310.

[0022] In this embodiment, the injection oil circuit 400 is used to perform action control. It includes a first cartridge valve 410 fluidly connected to the injection chamber 210 and a second cartridge valve 420 fluidly connected to the ejection chamber 220. High-frequency, high-precision control of injection, pressure holding, ejection, and material storage back pressure actions is mainly achieved by the first cartridge valve 410. The first cartridge valve 410 is a three-position, three-way proportional servo cartridge valve. This three-position, three-way proportional servo cartridge valve has a first port fluidly connected to the first accumulator 310, a second port fluidly connected to the injection chamber 210, and a third port fluidly connected to the oil tank 100. Furthermore, this three-position, three-way proportional servo cartridge valve has a conducting position that allows the second port to selectively connect to either the first or third port, and a closing position that simultaneously blocks the first, second, and third ports from each other. In other words, the three-position, three-way proportional servo cartridge valve has… There are three positions. In the first position, the first oil port and the second oil port are in fluid communication. At this time, the first accumulator 310 and the injection chamber 210 are connected, which can realize high-pressure injection or pressure holding. In the second position, the second oil port and the third oil port are in fluid communication. At this time, the injection chamber 210 and the oil tank 100 are connected, which can realize the action of injection retraction or material storage back pressure. In the third position, the second oil port, the first oil port and the third oil port are cut off from each other. At this time, pressure holding can be performed. Since the opening size of the three-position three-way proportional servo cartridge valve is adjustable, the opening size of the three-position three-way proportional servo cartridge valve between the first position and the second position can be adjusted, thereby controlling the injection speed, pressure holding pressure and material storage back pressure. Multiple actions can be precisely controlled by using a single three-position three-way proportional servo cartridge valve. The entire injection system meets the requirements of high pressure, high speed, high frequency response and high precision, while reducing costs.

[0023] Furthermore, the three-position three-way proportional servo cartridge valve is equipped with an external control port. A first pilot oil circuit is provided between the external control port and the first accumulator 310. The first pilot oil circuit includes a first check valve 411 and an oil filter 412. The inlet of the first check valve 411 is fluidly connected to the first accumulator 310, and the outlet of the first check valve 411 is fluidly connected to the external control port via the oil filter 412. That is, the pilot control oil of the three-position three-way proportional servo cartridge valve is directly drawn from the first accumulator 310. The first accumulator 310 can absorb system pressure fluctuations and provide a relatively stable oil source for its connected oil circuits. Using this stable oil for the pilot control of the valve can avoid interference caused by instantaneous pressure fluctuations in the main system or pump source switching on the pilot control pressure. This ensures more stable and precise single-control of the 3-position 3-way proportional servo cartridge valve spool, improving the response consistency and stability of the entire injection control system. Simultaneously, the configuration of the first check valve 411 ensures that the oil can only flow from the first accumulator 310 to the valve's external control port, and cannot flow in the opposite direction. Since the 3-position 3-way proportional servo cartridge valve spool has extremely small clearance, it requires extremely high oil cleanliness. By arranging an oil filter 412 between the first check valve 411 and the external control port, particulate contaminants from the oil circuit of the first accumulator 310 can be effectively filtered, providing clean oil for the valve's pilot control section. This significantly reduces the risk of spool jamming or wear, ensuring long-term reliability and control accuracy, and extending the service life of the core valve components.

[0024] In this embodiment, in order to further improve the stability of the pilot oil of the three-position three-way proportional servo cartridge valve, the first pilot oil circuit also includes a second accumulator. The second accumulator is arranged between the oil filter 412 and the external control port, which can ensure a stable supply of pilot oil to the external control port.

[0025] The second cartridge valve 420 has a first working port and a second working port. The first working port is fluidly connected to the oil line between the first accumulator 310 and the first port. The second working port is fluidly connected to the injection chamber 220. During the injection process, the injection chamber 220 needs to drain oil. At this time, the second cartridge valve 420 is opened, and the oil flowing out of the injection chamber 220 will enter the oil line between the first accumulator 310 and the first port, thus flowing from the first port to the second port, and finally flowing into the injection chamber 210, realizing differential injection and improving the injection speed.

[0026] To achieve precise control of injection speed, holding pressure, and back pressure of the stored material, the injection cylinder 200 is equipped with a first pressure sensor 230, a second pressure sensor 240, and a position gauge 250. The first pressure sensor 230 is configured to detect the pressure in the injection chamber 210, the second pressure sensor 240 is configured to detect the pressure in the ejection chamber 220, and the position gauge 250 is configured to detect the displacement of the piston rod of the injection cylinder 200. A valve holder is provided on the three-position three-way proportional servo cartridge valve to control its valve core opening. This valve holder is electrically connected to the first pressure sensor 230, the second pressure sensor 240, and the position gauge 250. The system, consisting of a pressure sensor 230, a second pressure sensor 240, and a position gauge 250, can acquire three key physical quantities in real time and accurately: the pressure in the injection chamber 210, the pressure in the ejection chamber 220, and the displacement of the piston rod. After receiving the electrical signals from these sensors, the valve accelerator can compare them with preset process curves (such as speed-position and pressure-time curves) in real time. Based on the deviation, the valve accelerator dynamically and accurately adjusts the valve core opening of the three-position three-way proportional servo cartridge valve to achieve precise servo control of injection speed, holding pressure, and ejection action, forming a complete "measurement-comparison-correction" closed loop, which can significantly improve the quality of the injection molding process.

[0027] In order to control the charging and discharging of the first accumulator 310, the power oil circuit 300 also includes a third cartridge valve 320. The third cartridge valve 320 has a third working port and a fourth working port. The third working port is in fluid communication with both the first port and the first working port, and the fourth working port is in fluid communication with the first accumulator 310. The charging and discharging of the first accumulator 310 is determined by the opening and closing of the third cartridge valve 320.

[0028] Furthermore, the third cartridge valve 320 is provided with a first pilot chamber, and a second pilot oil passage is provided between the first pilot chamber and the third working oil port and the fourth working oil port. The second pilot oil passage includes a first shuttle valve 321, a first solenoid directional valve 322, and a second solenoid directional valve 323. The two oil inlets of the first shuttle valve 321 are in fluid communication with the third working oil port and the fourth working oil port, respectively. The oil outlet of the first shuttle valve 321 can be in fluid communication with the first pilot chamber via the first solenoid directional valve 322 and the second solenoid directional valve 323. The first solenoid directional valve 322 is provided with a first oil inlet, a second oil inlet, a first oil outlet, and a first electromagnet 322a. The second solenoid directional valve 323 is provided with a third oil inlet, a first variable oil port, and a second oil outlet. The oil outlet of 321 is fluidly connected to the first oil inlet, the fourth working oil port is fluidly connected to the second oil inlet, the first oil outlet is fluidly connected to the third oil inlet, the first variable oil port is fluidly connected to the first pilot chamber, and the second oil outlet is fluidly connected to the oil tank 100. The first electromagnetic reversing valve 322 is also equipped with a first electromagnet 322a. When the first electromagnet 322a is energized, the first oil inlet and the first oil outlet are fluidly connected. When the first electromagnet 322a is de-energized, the second oil inlet and the first oil outlet are fluidly connected. The second electromagnetic reversing valve 323 is also equipped with a second electromagnet 323a. When the second electromagnet 323a is energized, the first variable oil port and the second oil outlet are fluidly connected. When the second electromagnet 323a is de-energized, the third oil inlet and the first variable oil port are fluidly connected.

[0029] The third cartridge valve 320 has three control states. In one state, neither the first electromagnet 322a nor the second electromagnet 323a is energized. In this state, the hydraulic oil from the higher pressure side of the third and fourth working ports enters the outlet of the first shuttle valve 321, and then enters the first inlet of the first solenoid directional valve 322. At this time, since the first inlet and the first outlet are disconnected, the hydraulic oil at the outlet of the first shuttle valve 321 cannot enter the first pilot chamber. However, at this time, the second inlet and the first outlet are in fluid communication. The first oil outlet is fluidly connected to the third oil inlet, and the third oil inlet is fluidly connected to the first variable oil port. At this time, the pilot oil supplied at the fourth working oil port can enter the first pilot chamber. It should be noted that the pump set oil circuit 500 is fluidly connected to the third working oil port. Therefore, the pump set oil circuit 500 provides pressurized oil to open the third cartridge valve 320. However, since the fourth working oil port of the third cartridge valve 320 is fluidly connected to the first pilot chamber, the third cartridge valve 320 forms a one-way structure at this time, and the hydraulic oil can only flow from the third working oil port to the fourth working oil port. The first accumulator 310 can only perform charging operations at this time; the second is that the first electromagnet 322a is energized. At this time, the hydraulic oil on the higher pressure side of the third and fourth working ports will enter the outlet of the first shuttle valve 321, and then enter the first inlet of the first solenoid directional valve 322. At this time, the first inlet and the first outlet are fluidly connected. The pilot oil will flow from the first outlet through the third inlet and the first variable port until it enters the first pilot chamber. At this time, the third cartridge valve 320 is closed, and the pump group oil circuit 5... The hydraulic oil supplied by 00 cannot charge the first accumulator 310 through the third cartridge valve 320, and the first accumulator 310 stops charging. The third option is that the second electromagnet 323a is energized. At this time, the hydraulic oil in the first pilot chamber can return to the oil tank 100 through the first variable oil port and the second oil outlet. At this time, the third cartridge valve 320 is fully opened. Whether there is pressurized oil on the third working oil port or the fourth working oil port side, the third cartridge valve 320 can be opened. At this time, the first accumulator 310 can be charged and then released or charged while releasing energy.

[0030] Of course, in order to improve the safety performance of the first accumulator 310, the power oil circuit 300 also includes a manual pressure relief valve, a safety valve and a power failure pressure relief valve, all of which are arranged in the oil circuit between the first accumulator 310 and the third cartridge valve 320.

[0031] Specifically, the pump set oil circuit 500 includes a system oil port 510 and a second check valve 520. The system oil port 510 is fluidly connected to the third working oil port through the second check valve 520. The second check valve 520 is configured to open from the system oil port 510 toward the third working oil port. The system oil port 510 provides initial hydraulic oil to the first accumulator 310 for energy storage. The second check valve 520 can prevent the hydraulic oil in the first accumulator 310 from flowing back into the system oil port 510.

[0032] Furthermore, a second pilot chamber is provided on the second cartridge valve 420. A third pilot oil passage is provided between the second pilot chamber and the first working oil port and the second working oil port. The third pilot oil passage includes a second shuttle valve 421 and a third solenoid directional valve 422. The two oil inlets of the second shuttle valve 421 are in fluid communication with the first working oil port and the second working oil port, respectively. The oil outlet of the second shuttle valve 421 can be in fluid communication with the second pilot chamber through the third solenoid directional valve 422. The pilot oil of the third pilot oil passage also comes from the first accumulator 310, which can control whether the second cartridge valve 420 is opened or closed.

[0033] Specifically, the injection oil circuit 400 also includes a replenishing oil check valve 430, which is arranged between the oil tank 100 and the injection chamber 220 and configured with its opening facing the injection chamber 220. When performing the material storage operation, the oil tank 100 can replenish oil to the injection chamber 220 through the replenishing oil check valve 430 to prevent the oil cylinder from sucking in air and damaging the injection cylinder 200.

[0034] The technical solution of the present invention has been described in detail above with reference to the accompanying drawings. The described embodiments are used to help understand the concept of the present invention. The specific embodiments described herein are merely illustrative examples of the spirit of the present invention. Those skilled in the art to which this invention pertains can make various modifications or additions to the described specific embodiments or use similar methods to replace them, but without departing from the spirit of the present invention or exceeding the scope defined by the appended claims.

[0035] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0036] Furthermore, in this invention, descriptions involving terms such as "first," "second," and "a" are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0037] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean fluid communication within two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A hydraulic circuit for an injection system of an injection molding machine, characterized in that, It includes an oil tank, an injection cylinder, a power oil circuit, and an injection oil circuit, wherein the injection cylinder has an injection chamber and an ejection chamber; wherein, The power oil circuit includes a first accumulator; The injection circuit includes a first cartridge valve and a second cartridge valve. The first cartridge valve is configured as a three-position three-way proportional servo cartridge valve. The three-position three-way proportional servo cartridge valve has a first port that is fluidly connected to the first accumulator, a second port that is fluidly connected to the injection chamber, and a third port that is fluidly connected to the oil tank. The three-position three-way proportional servo cartridge valve has a conducting position that allows the second port to be fluidly connected to either the first port or the third port, and a closing position that cuts off the first port, the second port, and the third port from each other. The second cartridge valve has a first working port and a second working port. The first working port is in fluid communication with the oil line between the first accumulator and the first port, and the second working port is in fluid communication with the ejection chamber.

2. The hydraulic circuit of the injection system of an injection molding machine according to claim 1, characterized in that, The injection cylinder is also equipped with a first pressure sensor, a second pressure sensor, and a position ruler. The first pressure sensor is configured to detect the pressure in the injection chamber, the second pressure sensor is configured to detect the pressure in the ejection chamber, and the position ruler is configured to detect the displacement of the piston rod of the injection cylinder. The three-position three-way proportional servo cartridge valve is equipped with a valve clip for controlling the valve core opening. The valve clip is electrically connected to the first pressure sensor, the second pressure sensor, and the position ruler.

3. The hydraulic circuit of the injection system of an injection molding machine according to claim 1, characterized in that, The three-position three-way proportional servo cartridge valve is provided with an external control oil port. A first pilot oil circuit is provided between the external control oil port and the first accumulator. The first pilot oil circuit includes a first check valve and an oil filter. The oil inlet of the first check valve is in fluid communication with the first accumulator, and the oil outlet of the first check valve is in fluid communication with the external control oil port through the oil filter.

4. The hydraulic circuit of the injection system of an injection molding machine according to claim 1, characterized in that, The power oil circuit also includes a third cartridge valve, which has a third working port and a fourth working port. The third working port is in fluid communication with both the first port and the first working port, and the fourth working port is in fluid communication with the first accumulator.

5. The hydraulic circuit of an injection molding machine injection system according to claim 4, characterized in that, The third cartridge valve is provided with a first pilot chamber, and a second pilot oil passage is provided between the first pilot chamber and the third working oil port and the fourth working oil port; The second pilot oil circuit includes a first shuttle valve, a first solenoid directional valve, and a second solenoid directional valve. The two inlets of the first shuttle valve are in fluid communication with the third working port and the fourth working port, respectively. The outlet of the first shuttle valve can be in fluid communication with the first pilot chamber via the first solenoid directional valve and the second solenoid directional valve.

6. The hydraulic circuit of the injection system of an injection molding machine according to claim 5, characterized in that, The first electromagnetic directional valve is provided with a first oil inlet, a second oil inlet, a first oil outlet, and a first electromagnet. The second electromagnetic directional valve is provided with a third oil inlet, a first variable oil inlet, and a second oil outlet. The oil outlet of the first shuttle valve is in fluid communication with the first oil inlet. The fourth working oil inlet is in fluid communication with the second oil inlet. The first oil outlet is in fluid communication with the third oil inlet. The first variable oil inlet is in fluid communication with the first pilot chamber. The second oil outlet is in fluid communication with the oil tank.

7. The hydraulic circuit of an injection molding machine injection system according to claim 6, characterized in that, The first electromagnetic reversing valve is also equipped with a first electromagnet. When the first electromagnet is energized, the first oil inlet and the first oil outlet are in fluid communication. When the first electromagnet is de-energized, the second oil inlet and the first oil outlet are in fluid communication. The second electromagnetic reversing valve is also equipped with a second electromagnet. When the second electromagnet is energized, the first variable oil port is in fluid communication with the second oil outlet. When the second electromagnet is de-energized, the third oil inlet is in fluid communication with the first variable oil port.

8. The hydraulic circuit of the injection system of an injection molding machine according to claim 4, characterized in that, It also includes a pump set oil circuit, which includes a system oil port and a second check valve. The system oil port is in fluid communication with the third working oil port through the second check valve. The second check valve is configured to open from the system oil port toward the third working oil port.

9. The hydraulic circuit of the injection system of an injection molding machine according to claim 4, characterized in that, The second cartridge valve is also provided with a second pilot chamber, and a third pilot oil passage is provided between the second pilot chamber and the first working oil port and the second working oil port; The third pilot oil circuit includes a second shuttle valve and a third solenoid directional valve. The two inlets of the second shuttle valve are in fluid communication with the first working oil port and the second working oil port, respectively. The outlet of the second shuttle valve can be in fluid communication with the second pilot chamber through the third solenoid directional valve.

10. The hydraulic circuit of an injection molding machine injection system according to claim 1, characterized in that, The injection circuit also includes a replenishing check valve, which is arranged between the oil tank and the injection chamber and configured with its opening facing the injection chamber.

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