A plunger hydraulic system with high precision and high pressure

Abstract

The application discloses a high-precision and high-pressure injection hydraulic system, which comprises an injection cylinder, a pressure boosting cylinder and a valve module connected through an oil circuit; in a rapid injection stage, a tracking stage and a pressure boosting injection stage, an oil pump and an oil tank of the oil circuit can be communicated to form an A-type half-bridge structure. The application has the beneficial effects that the A-type half-bridge structure can be used to control the speed of the injection cylinder and the pressure boosting pressure of the pressure boosting cylinder; compared with a traditional mode, the speed overshoot can be effectively avoided or reduced, and meanwhile, the pressure stability and control precision of the pressure boosting injection can be ensured. When high-speed injection is performed, the number of switch valves required for connecting the rodless cavity of the injection cylinder and the accumulator oil circuit can be reduced, the throttling loss during high-speed injection can be reduced, and thus the dynamic injection force of the injection cylinder can be effectively improved.

Description

Technical Field

[0001] This application relates to the field of metal die casting technology, and in particular to a high-precision and high-pressure injection hydraulic system. Background Technology

[0002] A die-casting machine is a machine used for pressure casting, commonly used in the production and processing of automotive parts. Under pressure, the die-casting machine injects molten metal into a mold to cool and solidify, resulting in a solid metal casting after the mold is opened.

[0003] The injection process of existing cold chamber die casting machines consists of three stages: slow injection, fast injection, and pressurized injection. Before proceeding with pressurized injection after the fast injection, the injection cylinder needs to be braked. After the die casting machine completes the injection process, it also needs to undergo a pressure relief process, a tracking process, and a hammer return process to return to the initial position.

[0004] However, existing high-precision and high-pressure injection hydraulic systems may encounter the following issues when performing the above process:

[0005] (1) There may be a starting shock during the slow start-up phase, and the precision control is poor.

[0006] (2) Speed ​​overshoot may occur during the rapid injection phase.

[0007] (3) During the boost injection stage, there may be excessive or insufficient oil discharge, which may result in poor accuracy of boost pressure.

[0008] (4) During the braking phase, the braking may be slow, resulting in an unsatisfactory braking effect.

[0009] (5) During the tracking phase, the hammer may become uncontrollable, which may lead to tracking failure.

[0010] Therefore, there is an urgent need to improve the existing high-precision and high-pressure injection hydraulic system. Summary of the Invention

[0011] One objective of this application is to provide a pressure injection hydraulic system that can solve at least one of the defects in the aforementioned background technology.

[0012] To achieve at least one of the above objectives, the technical solution adopted in this application is as follows: a high-precision and high-pressure injection hydraulic system, comprising an accumulator, an injection cylinder, a booster cylinder, and a valve module connected by an oil circuit; in the rapid injection stage, the braking stage, and the tracking stage, the valve module connects the rod chamber of the injection cylinder to the oil pump and the oil tank of the oil circuit respectively to form an A-type half-bridge structure; simultaneously, the accumulator is adapted to supply oil to the rodless chamber of the injection cylinder; in the booster injection stage, the valve module connects the rod chamber of the booster cylinder to the oil pump and the oil tank of the oil circuit respectively to form an A-type half-bridge structure.

[0013] Preferably, the valve module includes a switching valve V5, servo valves V7 and V9, and a check valve V11; the output end of the oil pump is connected to the rod chamber of the injection cylinder through the check valve V11 and the servo valve V9 connected in series to form a first oil circuit; the accumulator is connected to the rodless chamber of the injection cylinder through the switching valve V5 to form a fourth oil circuit; the oil tank is connected to the rod chamber of the injection cylinder through the servo valve V7 to form a fifth oil circuit; during rapid injection and braking phases, the accumulator supplies oil to the rodless chamber of the injection cylinder through the connected fourth oil circuit; simultaneously, the pressurized oil in the rod chamber of the injection cylinder flows back to the oil tank along the connected fifth oil circuit; at this time, the oil pump supplies oil to the first oil circuit so that the first oil circuit and the fifth oil circuit form an A-type half-bridge structure at the intersection of the rod chamber of the injection cylinder, thereby adjusting the injection speed of the injection cylinder by controlling the opening of the servo valves V7 and V9.

[0014] Preferably, the valve module further includes a switching valve V8 and a check valve V13; the output end of the oil pump is connected to the rodless chamber of the injection cylinder through a series of check valves V11, V13, switching valve V8, and switching valve V5 to form a third oil circuit; during the tracking phase, the third oil circuit is opened based on the oil circuit structure corresponding to the rapid injection phase, so that the oil pump supplies oil to the rodless chamber of the injection cylinder through the opened third oil circuit; at this time, the follow-up speed of the hammer is adjusted by controlling the opening of servo valves V7 and V9.

[0015] Preferably, the valve module further includes switching valves V4 and V6; the accumulator is connected to the rodless chamber of the booster cylinder via switching valve V4 to form a sixth oil circuit; the oil tank is connected to the rod chamber of the booster cylinder via a servo valve V7 and a switching valve V6 connected in series to form a seventh oil circuit; the output end of the oil pump is connected to the rod chamber of the booster cylinder via a check valve V11, a servo valve V9, and a switching valve V6 connected in series to form an eighth oil circuit; during the booster injection stage, the accumulator... Oil is supplied to the rodless chamber of the booster cylinder through the sixth oil passage; the pressurized oil in the rod chambers of the booster cylinder and the injection cylinder flows back to the oil tank through the seventh and fifth oil passages, respectively; at this time, the oil pump supplies oil to the eighth oil passage, so that the intersection of the eighth oil passage and the seventh oil passage at the rod chamber of the booster cylinder forms an A-type half-bridge structure, and then the booster pressure of the booster cylinder is adjusted by controlling the opening of the servo valves V9 and V7.

[0016] Preferably, when depressurizing after the pressurization and injection stage is completed, the accumulator stops supplying oil to the rodless chamber of the pressurization cylinder, and the opening of servo valve V9 is increased while the opening of servo valve V7 is decreased, so that the oil pump supplies oil to the rod chamber of the pressurization cylinder through the connected eighth oil passage, thereby causing the pressurization cylinder to retract and return the pressurized oil in the rodless chamber to the accumulator along the connected sixth oil passage.

[0017] Preferably, the valve module further includes switching valves V10 and V15; the oil tank is connected to the rodless chamber of the booster cylinder via switching valve V10 to form a ninth oil circuit; the oil tank is connected to the rodless chamber of the injection cylinder via switching valve V15 to form a tenth oil circuit; during the return hammer stage after the tracking stage is completed, the oil pump supplies oil to the rod chamber of the injection cylinder and the booster cylinder respectively through the connected first oil circuit and the eighth oil circuit; at the same time, the rodless chamber of the injection cylinder and the booster cylinder respectively return the pressurized oil to the oil tank through the connected tenth oil circuit and the ninth oil circuit.

[0018] Preferably, the valve module further includes a switching valve V4 and servo valves V15 and V16; the accumulator is connected to the rodless chamber of the booster cylinder via the switching valve V4 to form a sixth oil circuit; the accumulator is connected to the rod chamber of the booster cylinder via the servo valve V15 to form an eleventh oil circuit; the oil tank is connected to the rod chamber of the booster cylinder via the servo valve V16 to form a twelfth oil circuit; during the booster injection stage, the accumulator supplies oil to the rodless chamber of the booster cylinder through the connected sixth oil circuit. Oil is supplied to the injection cylinder; the pressurized oil in the rod chamber of the injection cylinder flows back to the oil tank along the fifth oil passage; at the same time, the pressurized oil in the rod chamber of the booster cylinder flows back to the oil tank along the twelfth oil passage; at this time, the accumulator supplies oil to the eleventh oil passage, so that the eleventh oil passage and the twelfth oil passage form an A-type half-bridge structure at the intersection of the rod chamber of the booster cylinder, and then the booster pressure of the booster cylinder is adjusted by controlling the opening of servo valve V15 and servo valve V16.

[0019] Preferably, when depressurizing after the pressurization and injection stage is completed, the fifth and twelfth oil circuits are shut off; at the same time, the sixth and eleventh oil circuits are kept open, but the accumulator stops supplying oil to the sixth oil circuit, so that the accumulator supplies oil to the rod chamber of the pressurization cylinder through the eleventh oil circuit, and then the pressurization cylinder retracts and the pressurized oil in the rodless chamber flows back to the accumulator along the open sixth oil circuit.

[0020] Preferably, the valve module further includes switching valves V10, V12, and V14; the oil tank is connected to the rodless chamber of the booster cylinder via switching valve V10 to form a ninth oil circuit; the oil tank is connected to the rodless chamber of the injection cylinder via switching valve V14 to form a tenth oil circuit; the oil pump is connected to the rod chamber of the booster cylinder via switching valve V12 and servo valve V15 connected in series to form a thirteenth oil circuit; during the return hammer stage after the tracking stage is completed, the oil pump supplies oil to the rod chambers of the injection cylinder and the booster cylinder through the first and thirteenth oil circuits respectively; at the same time, the rodless chambers of the injection cylinder and the booster cylinder return the pressurized oil to the oil tank through the tenth and ninth oil circuits respectively.

[0021] Preferably, during the slow injection phase, the oil pump supplies oil to the rodless chamber of the injection cylinder through the connected third oil circuit, and the accumulator supplies oil to the rodless chamber of the injection cylinder through the connected fourth oil circuit; at the same time, the first oil circuit is connected and connected to the third oil circuit to form a differential circuit.

[0022] Compared with the prior art, the beneficial effects of this application are as follows:

[0023] (1) The oil circuit is designed to obtain an A-type half-bridge structure, which can be used to control the speed of the injection cylinder and the boosting pressure of the boosting cylinder. Compared with the traditional method, it can effectively avoid or reduce speed overshoot, and at the same time ensure the pressure stability and control accuracy of boosting injection.

[0024] (2) During high-speed injection, by reducing the number of switching valves required to connect the rodless chamber of the injection cylinder to the accumulator, the throttling loss during high-speed injection can be reduced, thereby effectively improving the dynamic injection force of the injection cylinder. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the oil circuit structure of the injection system corresponding to Embodiment 1 of the present invention.

[0026] Figure 2 This is an equivalent schematic diagram of the oil circuit in the energy storage stage of Embodiment 1 of the present invention.

[0027] Figure 3 This is an equivalent schematic diagram of the oil circuit in the slow injection stage of Embodiment 1 of the present invention.

[0028] Figure 4 This is an equivalent schematic diagram of the oil circuit during the rapid injection stage and the braking stage of Embodiment 1 of the present invention.

[0029] Figure 5 This is an equivalent schematic diagram of the oil circuit in the pressurization delay stage of Embodiment 1 of the present invention.

[0030] Figure 6 This is an equivalent schematic diagram of the oil circuit in the pressurization and loading stage of Embodiment 1 of the present invention.

[0031] Figure 7 This is an equivalent schematic diagram of the oil circuit in the depressurization stage of Embodiment 1 of the present invention.

[0032] Figure 8 This is an equivalent schematic diagram of the oil circuit during the tracking stage of Embodiment 1 of the present invention.

[0033] Figure 9 This is an equivalent schematic diagram of the oil circuit in the retraction stage of Embodiment 1 of the present invention.

[0034] Figure 10 This is a partial schematic diagram of the relationship curves between injection position, injection speed, and casting pressure in a traditional injection system.

[0035] Figure 11 This is a partial schematic diagram of the relationship curve between injection position, injection speed and casting pressure in this invention.

[0036] Figure 12 This is a schematic diagram of the oil circuit structure of the injection system corresponding to Embodiment 2 of the present invention.

[0037] Figure 13 This is an equivalent schematic diagram of the oil circuit in the energy storage stage of Embodiment 2 of the present invention.

[0038] Figure 14 This is an equivalent schematic diagram of the oil circuit in the slow injection stage of Embodiment 2 of the present invention.

[0039] Figure 15 This is an equivalent schematic diagram of the oil circuit during the rapid injection stage and the braking stage of Embodiment 2 of the present invention.

[0040] Figure 16 This is an equivalent schematic diagram of the oil circuit in the pressurization delay stage of Embodiment 2 of the present invention.

[0041] Figure 17 This is an equivalent schematic diagram of the oil circuit in the pressurization and loading stage of Embodiment 2 of the present invention.

[0042] Figure 18 This is an equivalent schematic diagram of the oil circuit in the depressurization stage of Embodiment 2 of the present invention.

[0043] Figure 19 This is an equivalent schematic diagram of the oil circuit during the tracking stage in Embodiment 2 of the present invention.

[0044] Figure 20 This is an equivalent schematic diagram of the oil circuit in the retraction stage of Embodiment 2 of the present invention.

[0045] In the diagram: Injection cylinder 1, booster cylinder 2, accumulator 3. Detailed Implementation

[0046] The present application will be further described below with reference to specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0047] In the description of this application, it should be noted that the directional terms such as "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this application.

[0048] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0049] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0050] This application provides a high-precision and high-pressure injection hydraulic system, such as... Figures 1 to 20 As shown, one preferred embodiment includes an accumulator 3, an injection cylinder 1, a booster cylinder 2, and a valve module connected via an oil circuit. During the rapid injection phase, braking phase, and tracking phase, the valve module connects the rod-side chamber of the injection cylinder 1 to the oil pump and oil tank in the oil circuit, respectively, to form an A-type half-bridge structure. At this time, the accumulator 3 can supply oil to the rodless chamber of the injection cylinder 1 to ensure the smooth operation of the rapid injection phase, braking phase, and tracking phase. During the booster injection phase, the valve module connects the rod-side chamber of the booster cylinder 2 to the oil pump and oil tank in the oil circuit, respectively, to form an A-type half-bridge structure.

[0051] It should be understood that during the rapid injection phase of a traditional injection system, due to inertia, the maximum injection speed achievable by injection cylinder 1 is generally higher than the set target speed; this is reflected in the speed curve as a bulge, known as high-speed overshoot. During the booster injection phase, because the response of the servo valve in the oil circuit always lags behind the control cycle of the control system, this will lead to insufficient or excessive oil discharge from booster cylinder 2, thus affecting the accuracy of the booster pressure. During the tracking phase, because the pressure in the rodless chamber of injection cylinder 1 is too high after boosting, and there is insufficient oil in the rod chamber, the compressed oil in the rodless chamber pushes the hammer forward during mold opening, causing the hammer to become uncontrollable, thus leading to tracking loss of control.

[0052] In this embodiment, during the rapid injection and tracking stages, the rod chamber of injection cylinder 1 can be connected to the oil pump and oil tank in the oil circuit via a valve module to form an A-type half-bridge structure. Similarly, during the pressurized injection stage, the rod chamber of pressurized cylinder 2 can be connected to the oil pump and oil tank in the oil circuit via a valve module to form an A-type half-bridge structure. The A-type half-bridge structure is a linkage control structure composed of two servo valves, capable of simultaneously controlling the injection speed and casting pressure of the cylinder. This improves the accuracy of injection speed and pressure control while significantly reducing costs.

[0053] In this application, there are various specific oil circuit structures for the injection system capable of achieving the above functions; for ease of understanding, two specific embodiments are described below. Of course, the specific oil circuit structures include, but are not limited to, the two embodiments described below; wherein, Figures 2 to 9 as well as Figures 13 to 20 A thick solid line indicates a connected oil circuit, while a dashed line indicates a disconnected oil circuit; the oil pump is represented by P, and the oil tank is represented by T.

[0054] Example 1:

[0055] like Figures 1 to 9 As shown, the valve module includes switching valves V4 to V6, as well as V8, V10, and V12; servo valves V7 and V9; and check valves V11 and V13. The output of the oil pump is connected to the rod chamber of the injection cylinder 1 via a series of check valves V11 and servo valve V9 to form a first oil circuit; the output of the oil pump is connected to the accumulator 3 via a switching valve V12 to form a second oil circuit; the output of the oil pump is connected to the rodless chamber of the injection cylinder 1 via a series of check valves V11, V13, switching valve V8, and switching valve V5 to form a third oil circuit; the accumulator 3 is connected to the rodless chamber of the injection cylinder 1 via a switching valve V5 to form a fourth oil circuit; the oil tank is connected to the rod chamber of the injection cylinder 1 via a servo valve V7 to form a fourth oil circuit. The fifth oil circuit is formed; the accumulator 3 is connected to the rodless chamber of the booster cylinder 2 through the switching valve V4 to form the sixth oil circuit; the oil tank is connected to the rod chamber of the booster cylinder 2 through the servo valve V7 and the switching valve V6 connected in series to form the seventh oil circuit; the output end of the oil pump is connected to the rod chamber of the booster cylinder 2 through the check valve V11, the servo valve V9 and the switching valve V6 connected in series to form the eighth oil circuit; the oil tank is connected to the rodless chamber of the booster cylinder 2 through the switching valve V10 to form the ninth oil circuit; the oil tank is connected to the rodless chamber of the injection cylinder 1 through V14 to form the tenth oil circuit.

[0056] It should be noted that the function of the switching valve V12 is to control the oil pump to charge the accumulator 3.

[0057] The oil in the accumulator 3 can enter the rodless chamber of the booster cylinder 2 and the injection cylinder 1 through the switching valves V4 and V5 respectively. Specifically, the function of the switching valve V5 is to allow the oil in the accumulator 3 to flow directly into the rodless chamber of the injection cylinder 1 during the injection process. Compared with the traditional multi-switching valve oil circuit, it can reduce the throttling loss during high-speed injection, thereby effectively improving the dynamic injection force of the injection cylinder 1. Furthermore, the closing of the switching valve V5 during booster injection can prevent the high-pressure oil from flowing out, and the oil in the rodless chamber of the injection cylinder 1 can be discharged during the hammer return phase.

[0058] Switching valve V4 is directly connected to the rodless chamber of booster cylinder 2. During booster injection, the oil in accumulator 3 will enter the rodless chamber of booster cylinder 2 through switching valve V4. Switching valve V8, which is connected to switching valve V5, is used to differentially connect the oil in the rod chamber of injection cylinder 1 after passing through servo valve V9, and the oil from check valves V11 and V13, through switching valve V8.

[0059] Servo valve V9 and switching valve V5 are connected to the rodless chamber of injection cylinder 1. During slow injection, servo valve V9 controls the return oil speed of the rodless chamber of injection cylinder 1. During rapid injection, servo valves V9 and V7 can form an A-type half-bridge structure by intersecting in the rod chamber of injection cylinder 1 through oil circuits to control the rapid injection speed. During pressurized injection, switching valve V6 is opened, and servo valves V9 and V7 can also form an A-type half-bridge structure by intersecting in the rod chamber of pressurized cylinder 2 through oil circuits to control the pressurization pressure of pressurized cylinder 2. Specifically, switching valve V6 is connected to the rod chamber of pressurized cylinder 2, and its function is to control whether pressurization is activated.

[0060] Switching valves V10 and V14 connect the rodless chambers of booster cylinder 2 and injection cylinder 1 to the oil tank, respectively. Their function is to allow the oil in the rodless chambers of booster cylinder 2 and injection cylinder 1 to be discharged back into the oil tank during the return hammer operation.

[0061] The function of check valve V11 is to prevent hydraulic oil backflow caused by excessively high oil pressure after check valve V11.

[0062] The entire injection process of the injection system in this embodiment can be divided into the following stages: energy storage stage, slow injection stage, fast injection stage, braking stage, pressurization delay stage, pressurization injection stage, depressurization stage, tracking stage, and hammer return stage. For ease of understanding, the specific working process of each stage will be described in detail below.

[0063] I. Energy Storage Stage; such as Figure 2 As shown, the control system of the injection system can control the servo valve V9 and the switching valve V12 to be open, thus the first oil circuit and the second oil circuit are in a conducting state. This allows the oil pump to start and supply oil to the rod chamber of the injection cylinder 1 through the open first oil circuit, while simultaneously supplying oil to the accumulator 3 through the open second oil circuit. By supplying oil to the rod chamber of the injection cylinder 1 to build up pressure before the slow injection stage, the starting impact during the slow injection stage can be reduced or avoided.

[0064] II. Slow injection phase; such as Figure 3As shown, after the energy storage stage is completed, servo valve V9 and switching valve V12 are kept open, and switching valves V5 and V8 are also opened. At this time, the first, second, third, and fourth oil circuits are all open, and the first and third oil circuits intersect at the output of check valve V11 to form a differential circuit. That is, the oil pump supplies oil to the rodless chamber of the injection cylinder 1 through the open third oil circuit, and the accumulator 3 can also supply oil to the rodless chamber of the injection cylinder 1 through the open fourth oil circuit. At the same time, the oil pump can also replenish oil to the accumulator 3 through the open second oil circuit to ensure that the pressure in the accumulator 3 can always meet the usage requirements; then the pressure oil in the rod chamber of the injection cylinder 1 can flow into the rodless chamber of the injection cylinder 1 through the servo valve 9, sequentially through check valve V13, switching valve V5, and V8.

[0065] Understandably, differential control is used during the slow injection phase. This ensures stable slow injection while simultaneously controlling the flow rate in the rod chamber of injection cylinder 1 via servo valve V9 to regulate the slow injection speed. Furthermore, in differential control, the pressure difference between the servo valve V9 and its downstream side is smaller than that under traditional single-outlet control, resulting in a smaller pressure gain for servo valve V9 and thus improving the control accuracy of injection cylinder 1. Additionally, since pressure has been built into the rod chamber of injection cylinder 1 during the energy storage phase before slow injection begins, the compression of the oil in the rod chamber is reduced during slow injection startup, preventing or minimizing startup shock.

[0066] It is also understandable that in the actual injection process, the stroke of slow injection accounts for the majority. In this embodiment, by establishing a differential circuit, the flow rate required for slow injection by the injection cylinder 1 can be less than the flow rate required by traditional non-differential control. Furthermore, the oil pump and accumulator 3 supply oil together, which can further reduce the amount of oil supplied to the outside by the accumulator 3, and thus appropriately reduce the volume of the accumulator 3.

[0067] III. Rapid injection phase and braking phase; such as Figure 4 As shown, servo valve V7 is opened, switching valves V8 and V12 are closed, and switching valve V5 remains open. At this time, the first, fourth, and fifth oil circuits are all open, and the first and fifth oil circuits intersect at the rod chamber of the injection cylinder 1. The accumulator 3 then supplies oil to the rodless chamber of the injection cylinder 1 through the open fourth oil circuit; simultaneously, the pressurized oil in the rod chamber of the injection cylinder 1 flows back to the oil tank along the open fifth oil circuit; at this time, the oil pump supplies oil to the first oil circuit, so that the intersection of the first and fifth oil circuits at the rod chamber of the injection cylinder 1 forms an A-type half-bridge structure, and the injection speed of the injection cylinder 1 is adjusted by controlling the opening of servo valves V7 and V9.

[0068] Understandably, during the rapid injection phase, the servo valve V7 has a large opening, while the servo valve V9 has a small opening, allowing the pressurized oil in the rod chamber of injection cylinder 1 to quickly flow back to the oil tank, thus generating a faster injection speed. By activating the first oil circuit during the rapid injection phase to form an A-type half-bridge structure, the flow rate in the rod chamber of injection cylinder 1 can be rapidly adjusted by controlling the opening of servo valve V9, achieving precise speed control and reducing or avoiding high-speed overshoot.

[0069] Simultaneously, during the braking phase, the servo valve V7 has a small opening, while the servo valve V9 has a large opening, thereby increasing the pressure in the rod chamber of the injection cylinder 1 to achieve active braking. The oil pump's supply, through the A-type half-bridge structure, can more quickly build up pressure in the rod chamber of the injection cylinder 1, enabling faster deceleration and acceleration to complete the active braking action.

[0070] It is also understandable that in traditional injection systems, to meet the needs of the hydraulic system, the rodless chamber of the injection cylinder 1 generally requires two or more switching valves to connect to the accumulator 3; this results in significant throttling losses in the oil circuit during rapid injection. However, in this embodiment, the accumulator 3 is connected to the rodless chamber of the injection cylinder 1 through only one switching valve V5, thereby reducing the throttling losses in the oil circuit during rapid injection and thus improving the dynamic injection force of the injection cylinder 1.

[0071] IV. The boost delay phase, also known as the preparatory phase before the boost injection phase, can be considered a continuation of the braking phase; for example... Figure 5 As shown, after the injection speed of the injection cylinder 1 decreases to a set threshold, the switching valve V5 is closed, while the switching valve V4 is opened. Then, the servo valves V7 and V9 are adjusted to their preset positions. At this time, the sixth oil circuit is open, allowing the accumulator 3 to supply oil to the rodless chamber of the booster cylinder 2 through the open sixth oil circuit. By performing the preparatory action for boosting after the braking phase, the plateau period of casting pressure can be reduced. Furthermore, compared to the traditional passive closing method, this embodiment uses active opening and closing of the switching valves to ensure that the rodless chamber of the booster cylinder 2 always has pressure, thereby increasing the pressure build-up speed during boosting.

[0072] It should be noted that traditional injection systems directly proceed to the pressurization and injection phase after the braking phase, which can lead to issues such as... Figure 10 The pressure fluctuation is shown in the curve. In this embodiment, before the pressurized injection, that is, just before the braking phase ends, the switching valve V5 is closed to enter the pressurization delay phase. Because the closing speed of the switching valve V5 is very fast, it can greatly increase the braking speed, thereby reducing the fluctuation of the casting pressure. Figure 11 As shown.

[0073] V. Pressurized Injection Stage; such as Figure 6 As shown, based on the pressurization delay stage, the switching valve V6 is turned on. At this time, the sixth, seventh, and eighth oil circuits are all in the conducting state, and the seventh and eighth oil circuits intersect between the switching valve V6 and the servo valve V9. Then, the accumulator 3 can supply oil to the rodless chamber of the booster cylinder 2 through the conducting sixth oil circuit; the pressure oil in the rod chamber of the booster cylinder 2 flows back to the oil tank along the conducting seventh oil circuit; at this time, the oil pump can also supply oil to the eighth oil circuit, so that the intersection of the eighth and seventh oil circuits at the rod chamber of the booster cylinder 2 forms an A-type half-bridge structure, and then the booster pressure of the booster cylinder 2 is adjusted by controlling the opening of the servo valves V9 and V7.

[0074] It should be understood that since both servo valves V7 and V9 are in the conducting state, the first and fifth oil circuits are also correspondingly in the conducting state. Therefore, during the pressurized injection process, the rod chamber of injection cylinder 1 can be replenished or drained according to pressure requirements. That is, when the pressure in the rod chamber of injection cylinder 1 is low, oil can be replenished to the rod chamber through the first oil circuit; when the pressure in the rod chamber of injection cylinder 1 is high, oil can be drained from the rod chamber of injection cylinder 1 to reduce pressure through the fifth oil circuit. This avoids the loss of control during injection caused by the high pressure in the rodless chamber of injection cylinder 1 at the end of pressurized injection, while the rod chamber lacks oil, which is common in traditional oil circuits.

[0075] Understandably, the method for precisely controlling the boost pressure using the A-type half-bridge structure is as follows: In the delay phase before the boost pressure begins, to enable faster pressure build-up during the boost injection stage, servo valve V7 and servo valve V9 are opened to a preset fixed opening. When the pressure in the rodless chamber of injection cylinder 1 reaches a certain proportion of the first preset value, the opening of servo valve V7 is reduced to a certain set value. Then, the opening of servo valve V9 is adjusted to change the flow rate through it. This causes a pressure drop when the flow rate through servo valve V9 and the flow rate in the rod chamber of boost cylinder 2 flow through servo valve V7. This pressure drop is the pressure in the rod chamber of boost cylinder 2. By controlling the pressure in the rod chamber of boost cylinder 2, the boost pressure can be adjusted. Therefore, the flow rate can be controlled by adjusting the opening of servo valve V9, which in turn controls the pressure drop in servo valve V7, thus controlling the boost pressure. This control method allows for more precise adjustment of the boost pressure and enables the boost pressure to be adjusted from high to low, thus allowing for boost pressure correction after overshoot.

[0076] It should also be noted that during pressurized injection, the switching valve V12 can be opened, allowing the oil pump to replenish oil to the accumulator 3 through the opened second oil circuit. Replenishing oil to the accumulator 3 increases its pressure, ensuring sufficient pressure for subsequent tracking phases. Furthermore, the injection cylinder 1 and the pressurized cylinder 2 share a single accumulator 3, and oil replenishment is performed on the accumulator 3 during both the pressurized injection and slow injection phases, further reducing the accumulator 3's volume and lowering costs.

[0077] VI. Decompression Phase; such as Figure 7 As shown, the switching valve V12 is shut off to stop the oil pump from replenishing the accumulator 3; at the same time, the accumulator 3 stops supplying oil to the rodless chamber of the booster cylinder 2, and the opening of the servo valve V9 is increased and the opening of the servo valve V7 is decreased, so that the oil pump supplies oil to the rod chamber of the booster cylinder 2 through the connected eighth oil passage, and then the booster cylinder 2 retracts and the pressure oil in the rodless chamber flows back to the accumulator 3 along the connected sixth oil passage.

[0078] It should be noted that in traditional injection systems, after the pressurization injection stage is completed, the hammer head is required to eject the product from the fixed mold. Because the pressure in the rodless cavity of the injection cylinder 1 is too high after the pressurization injection stage is completed, and there is not enough oil in the rod cavity, the compressed oil in the rodless cavity will push the hammer head forward during the mold opening process, which will cause the hammer head to become uncontrollable and cause tracking loss.

[0079] In this embodiment, by increasing the opening of the servo valve V9, the pressure in the rod chamber of the booster cylinder 2 can be increased, causing the booster cylinder 2 to retract. This allows the pressurized oil in the rodless chamber of the booster cylinder 2 to flow back into the accumulator 3, thereby actively reducing the pressure in the rodless chamber of the injection cylinder 1. Based on force balance, this reduces the pressure in the rod chamber of the injection cylinder 1. Of course, during the depressurization phase, the pressure in the rodless chamber of the injection cylinder 1 is not completely removed; it is only reduced to the same level as the system pressure to ensure that excessive pressure in the rodless chamber does not lead to tracking loss of control.

[0080] VII. Follow-up Phase; such as Figure 8As shown, switch valves V4 and V6 are shut off, while switch valves V5 and V8 are opened for conduction. At this time, the first, third, fourth, and fifth oil circuits are all in a conducting state, and the first and fifth oil circuits intersect at the rod chamber position of the injection cylinder 1. Then, the accumulator 3 and the oil pump supply oil to the rodless chamber of the injection cylinder 1 through the conducting fourth and third oil circuits, respectively; at the same time, the pressurized oil in the rod chamber of the injection cylinder 1 flows back to the oil tank along the conducting fifth oil circuit; at this time, the oil pump can also supply oil to the first oil circuit, so that the intersection position of the first and fifth oil circuits at the rod chamber of the injection cylinder 1 forms an A-type half-bridge structure, and then the injection speed of the injection cylinder 1 is adjusted by controlling the opening degree of servo valves V7 and V9 to control the follow-up speed of the hammer head.

[0081] Specifically, after the pressure relief phase is complete, the hammer's follow-up speed can be controlled by increasing the opening of servo valve V7 and decreasing the opening of servo valve V9. Simultaneously, switching valve V12 can be opened to allow the oil pump to replenish oil to accumulator 3 via the second oil circuit, thereby ensuring pressure stabilization in accumulator 3 and increasing the hammer's follow-up pressure.

[0082] 8. The pullback phase; such as Figure 9 As shown, switch valves V5, V8, and V12, as well as servo valve V7, are closed, while switch valves V6, V10, and V14 are opened and energized, and servo valve V9 remains open. At this time, the first, eighth, ninth, and tenth oil circuits are all open. The oil pump then supplies oil to the rod chambers of injection cylinder 1 and booster cylinder 2 through the open first and eighth oil circuits, respectively; simultaneously, the rodless chambers of injection cylinder 1 and booster cylinder 2 return pressurized oil to the oil tank through the open tenth and ninth oil circuits, respectively.

[0083] It should be understood that by simultaneously supplying oil to the rod chambers of both the injection cylinder 1 and the booster cylinder 2 during the hammer return phase, the risk of dry grinding in the rod chambers during the hammer return phase of a traditional injection system can be avoided.

[0084] In this embodiment, the same servo valve V9 is used in the slow injection stage, fast injection stage, boost injection stage, tracking stage, and return hammer stage, and the same servo valves V7 and V9 are used in the fast injection stage, boost injection stage, and tracking stage. That is, the entire injection system uses only two servo valves, which can effectively reduce the cost of the injection system.

[0085] Example 2:

[0086] Compared to Embodiment 1, Embodiment 2 differs from Embodiment 1 in that it adds two servo valves, V15 and V16, while removing the switching valve V6. Specifically, as follows... Figures 12 to 20As shown, the valve module includes switching valves V4 to V5, V8, V10, V12, and V14, servo valves V7, V9, V15, and V16, and check valves V11 and V13. The output of the oil pump is connected to the rod chamber of the injection cylinder 1 via a series of check valves V11 and servo valve V9 to form a first oil circuit; the output of the oil pump is connected to the accumulator 3 via a switching valve V12 to form a second oil circuit; the output of the oil pump is connected to the rodless chamber of the injection cylinder 1 via a series of check valves V11, V13, switching valve V8, and switching valve V5 to form a third oil circuit; the accumulator 3 is connected to the rodless chamber of the injection cylinder 1 via a switching valve V5 to form a fourth oil circuit; the oil tank is connected to the rod chamber of the injection cylinder 1 via a servo valve V7 to form a fifth oil circuit; the accumulator... 3 is connected to the rodless chamber of booster cylinder 2 via switching valve V4 to form the sixth oil circuit; the oil tank is connected to the rodless chamber of booster cylinder 2 via switching valve V10 to form the ninth oil circuit; the oil tank is connected to the rodless chamber of injection cylinder 1 via switching valve V14 to form the tenth oil circuit; the accumulator 3 is connected to the rod chamber of booster cylinder 2 via servo valve V15 to form the eleventh oil circuit; the oil tank is connected to the rod chamber of booster cylinder 2 via servo valve V16 to form the twelfth oil circuit; the oil pump is connected to the rod chamber of booster cylinder 2 via switching valve V12 and servo valve V15 connected in series to form the thirteenth oil circuit.

[0087] In this embodiment, the entire injection process of the injection system can still be divided into the following stages: energy storage stage, slow injection stage, fast injection stage, braking stage, pressurization delay stage, pressurization injection stage, depressurization stage, tracking stage, and hammer return stage. For ease of understanding, the specific working process of each stage will be described in detail below.

[0088] I. Energy Storage Stage; such as Figure 13 As shown, the equivalent oil circuit structure in this embodiment is the same as that in Embodiment 1. Figure 2 The equivalent oil circuit structure shown is the same; therefore, it will not be described in detail here. For details, please refer to the energy storage stage of the above embodiment one.

[0089] II. Slow injection phase; such as Figure 14 As shown, the equivalent oil circuit structure in this embodiment is the same as that in Embodiment 1. Figure 3 The equivalent oil circuit structure shown is the same; therefore, it will not be described in detail here. For details, please refer to the slow injection stage of the above embodiment 1.

[0090] III. Rapid injection phase and braking phase; such as Figure 15 As shown, the equivalent oil circuit structure in this embodiment is the same as that in Embodiment 1. Figure 4 The equivalent oil circuit structure shown is the same; therefore, it will not be described in detail here. For details, please refer to the rapid injection stage and braking stage of the above embodiment 1.

[0091] IV. The pressurization delay phase, i.e., the preparation phase before the pressurization injection phase begins; such as... Figure 16 As shown, after the braking phase is completed, the switching valve V5 and servo valve V9 are closed, the switching valve V4 is opened, and the servo valve V7 remains open; at this time, both the fifth and sixth oil circuits are open. By performing a preparatory pressurization action after the braking phase is completed, the plateau period of casting pressure can be reduced.

[0092] V. Pressurized Injection Stage; such as Figure 17 As shown, based on the pressurization delay stage, servo valves V15 and V16 are opened and connected. At this time, the fifth, sixth, eleventh, and twelfth oil circuits are all in a connected state, and the eleventh and twelfth oil circuits intersect and connect at the rod chamber position of the pressurization cylinder 2. Then, the accumulator 3 supplies oil to the rodless chamber of the pressurization cylinder 2 through the connected sixth oil circuit; the pressurized oil in the rod chamber of the injection cylinder 1 flows back to the oil tank along the connected fifth oil circuit; at the same time, the pressurized oil in the rod chamber of the pressurization cylinder 2 flows back to the oil tank along the connected twelfth oil circuit. At this time, the accumulator 3 can also supply oil to the connected eleventh oil circuit, so that the intersection position of the eleventh and twelfth oil circuits at the rod chamber of the pressurization cylinder 2 forms an A-type half-bridge structure, and then the pressurization pressure of the pressurization cylinder 2 is adjusted by controlling the opening degree of servo valves V15 and V16.

[0093] It should be understood that the method for precisely controlling the booster pressure using the A-type half-bridge structure is as follows: Servo valve V7 is opened to a preset fixed opening, and servo valves V15 and V16 are also opened to preset fixed openings. When the pressure in the rodless chamber of injection cylinder 1 reaches a certain proportion of the first preset value, the opening of servo valve V16 is reduced to a certain set value. Then, the opening of servo valve V15 is adjusted to change the flow rate through servo valve V15, so that the flow rate through servo valve V15 and the flow rate in the rod chamber of booster cylinder 2 will generate a pressure drop when flowing through servo valve V16. This pressure drop is the pressure in the rod chamber of booster cylinder 2. By controlling the pressure in the rod chamber of booster cylinder 2, the booster pressure can be adjusted. Therefore, the flow rate can be controlled by adjusting the opening of servo valve V15, and thus the pressure drop in servo valve V16 can be controlled to control the booster pressure. This control method allows for more precise adjustment of the boost pressure and enables the boost pressure to be adjusted from high to low, thus allowing for boost pressure correction after overshoot.

[0094] It should also be noted that during the pressurization process, the switching valve V12 can be opened to open the second oil circuit, so that the oil pump can replenish the accumulator 3 through the second oil circuit to ensure that the accumulator 3 has sufficient pressure during the pressurization process.

[0095] VI. Decompression Phase; such as Figure 18As shown, after the pressurization and injection stage is completed, the switching valve V12 is closed, and the servo valves V7 and V16 are also closed, thus cutting off the second, fifth, and twelfth oil circuits. Simultaneously, the accumulator 3 stops supplying oil to the rodless chamber of the injection cylinder 2 through the sixth oil circuit, but the sixth and eleventh oil circuits remain open. The accumulator 3 can then supply oil to the rod chamber of the pressurization cylinder 2 through the open eleventh oil circuit, causing the pressurization cylinder 2 to retract and return the pressurized oil in the rodless chamber to the accumulator 3 along the open sixth oil circuit. At this time, the pressure in the rodless chamber of the injection cylinder 1 will decrease, but the pressure relief stage will not completely remove the pressure from the rodless chamber; it will only reduce the pressure to the same level as the system pressure to ensure that tracking control is not lost due to excessive pressure in the rodless chamber.

[0096] VII. Follow-up Phase; such as Figure 19 As shown, the equivalent oil circuit structure in this embodiment is the same as that in Embodiment 1. Figure 8 The equivalent oil circuit structure shown is the same; therefore, it will not be described in detail here. For details, please refer to the tracking stage of the above embodiment one.

[0097] 8. The pullback phase; such as Figure 20 As shown, after the tracking phase is completed, switching valves V5 and V8, as well as servo valve V7, are closed, while servo valve V15 is opened and kept open, and switching valve V12 and servo valve V9 remain open. At this time, the first, ninth, tenth, and thirteenth oil circuits are all in the open state. The oil pump then supplies oil to the rod chambers of injection cylinder 1 and booster cylinder 2 through the open first and thirteenth oil circuits, respectively; at the same time, the rodless chambers of injection cylinder 1 and booster cylinder 2 return the pressurized oil to the oil tank through the open tenth and ninth oil circuits, respectively.

[0098] It should be noted that when the switching valve V12 is turned on, the second oil circuit is also turned on. In this case, the oil pump can also replenish a portion of the oil to the accumulator 3 through the turned-on second oil circuit, thereby shortening the time of the energy storage stage in the next injection process.

[0099] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A high-precision and high-pressure injection hydraulic system, characterized in that, This includes an accumulator, injection cylinder, booster cylinder, and valve module connected via an oil circuit; The valve module includes switching valve V4, switching valve V5, switching valve V6, switching valve V8, servo valve V7, servo valve V9, check valve V11, and check valve V13. The output end of the oil pump is connected to the rod chamber of the injection cylinder via a series of one-way valves V11 and V9 to form a first oil circuit; the output end of the oil pump is connected to the rodless chamber of the injection cylinder via a series of one-way valves V11, V13, V8, and V5 to form a third oil circuit; the accumulator is connected to the rodless chamber of the injection cylinder via V5 to form a fourth oil circuit; the oil tank is connected to the rod chamber of the injection cylinder via a servo valve V7 to form a fifth oil circuit; the accumulator is connected to the rodless chamber of the booster cylinder via a V4 to form a sixth oil circuit; the oil tank is connected to the rod chamber of the booster cylinder via a series of servo valves V7 and V6 to form a seventh oil circuit; the output end of the oil pump is connected to the rod chamber of the booster cylinder via a series of one-way valves V11, V9, and V6 to form an eighth oil circuit. During the rapid injection and braking phases, the accumulator supplies oil to the rodless chamber of the injection cylinder through the fourth oil passage; simultaneously, the pressurized oil in the rod chamber of the injection cylinder flows back to the oil tank along the fifth oil passage; at this time, the oil pump supplies oil to the first oil passage, so that the first oil passage and the fifth oil passage form an A-type half-bridge structure at the intersection of the rod chamber of the injection cylinder, and then the injection speed of the injection cylinder is adjusted by controlling the opening of servo valves V7 and V9; During the tracking phase, the third oil circuit is opened based on the oil circuit structure corresponding to the rapid injection phase, so that the oil pump supplies oil to the rodless chamber of the injection cylinder through the opened third oil circuit; at this time, the follow-up speed of the hammer is adjusted by controlling the opening of servo valve V7 and servo valve V9. During the pressurization and injection stage, the accumulator supplies oil to the rodless chamber of the pressurization cylinder through the sixth oil passage; the pressurized oil in the rod chambers of the pressurization cylinder and the injection cylinder flows back to the oil tank through the seventh and fifth oil passages, respectively; at this time, the oil pump supplies oil to the eighth oil passage, so that the intersection of the eighth oil passage and the seventh oil passage at the rod chamber of the pressurization cylinder forms an A-type half-bridge structure, and then the pressurization pressure of the pressurization cylinder is adjusted by controlling the opening of the servo valves V9 and V7.

2. A high-precision and high-pressure injection hydraulic system, characterized in that, This includes an accumulator, injection cylinder, booster cylinder, and valve module connected via an oil circuit; The valve module includes switching valve V4, switching valve V5, switching valve V8, servo valve V7, servo valve V9, check valve V11, check valve V13, servo valve V15, and servo valve V16. The output end of the oil pump is connected to the rod chamber of the injection cylinder via a series of one-way valves V11 and V9 to form a first oil circuit; the output end of the oil pump is connected to the rodless chamber of the injection cylinder via a series of one-way valves V11, V13, V8, and V5 to form a third oil circuit; the accumulator is connected to the rodless chamber of the injection cylinder via V5 to form a fourth oil circuit; the oil tank is connected to the rod chamber of the injection cylinder via V7 to form a fifth oil circuit; the accumulator is connected to the rodless chamber of the booster cylinder via V4 to form a sixth oil circuit; the accumulator is connected to the rod chamber of the booster cylinder via V15 to form an eleventh oil circuit; and the oil tank is connected to the rod chamber of the booster cylinder via V16 to form a twelfth oil circuit. During the rapid injection and braking phases, the accumulator supplies oil to the rodless chamber of the injection cylinder through the fourth oil passage; simultaneously, the pressurized oil in the rod chamber of the injection cylinder flows back to the oil tank along the fifth oil passage; at this time, the oil pump supplies oil to the first oil passage, so that the first oil passage and the fifth oil passage form an A-type half-bridge structure at the intersection of the rod chamber of the injection cylinder, and then the injection speed of the injection cylinder is adjusted by controlling the opening of servo valves V7 and V9; During the tracking phase, the third oil circuit is opened based on the oil circuit structure corresponding to the rapid injection phase, so that the oil pump supplies oil to the rodless chamber of the injection cylinder through the opened third oil circuit; at this time, the follow-up speed of the hammer is adjusted by controlling the opening of servo valve V7 and servo valve V9. During the pressurization and injection stage, the accumulator supplies oil to the rodless chamber of the pressurization cylinder through the sixth oil passage; the pressurized oil in the rod chamber of the injection cylinder flows back to the oil tank along the fifth oil passage; simultaneously, the pressurized oil in the rod chamber of the pressurization cylinder flows back to the oil tank along the twelfth oil passage; at this time, the accumulator supplies oil through the eleventh oil passage, so that the eleventh oil passage and the twelfth oil passage form an A-type half-bridge structure at the intersection of the rod chamber of the pressurization cylinder, and then the pressurization pressure of the pressurization cylinder is adjusted by controlling the opening of servo valves V15 and V16.

3. The high-precision and high-pressure injection hydraulic system as described in claim 1, characterized in that: When depressurizing after the pressurization and injection stage is completed, the accumulator stops supplying oil to the rodless chamber of the pressurization cylinder, and the opening of servo valve V9 is increased while the opening of servo valve V7 is decreased. This allows the oil pump to supply oil to the rod chamber of the pressurization cylinder through the connected eighth oil passage. Consequently, the pressurization cylinder retracts and the pressurized oil in the rodless chamber flows back to the accumulator along the connected sixth oil passage.

4. The high-precision and high-pressure injection hydraulic system as described in claim 1, characterized in that: The valve module also includes on / off valves V10 and V14; The oil tank is connected to the rodless chamber of the booster cylinder via a switching valve V10 to form a ninth oil circuit; The oil tank is connected to the rodless chamber of the injection cylinder via a switching valve V14 to form a tenth oil circuit; During the return hammer phase after the tracking phase, the oil pump supplies oil to the rod chamber of the injection cylinder and the booster cylinder through the first and eighth oil circuits, respectively; at the same time, the rodless chambers of the injection cylinder and the booster cylinder return the pressurized oil to the oil tank through the tenth and ninth oil circuits, respectively.

5. The high-precision and high-pressure injection hydraulic system as described in claim 2, characterized in that: When depressurizing after the pressurization and injection stage, the fifth and twelfth oil circuits are shut off; at the same time, the sixth and eleventh oil circuits are kept open, but the accumulator stops supplying oil to the sixth oil circuit, so that the accumulator supplies oil to the rod chamber of the pressurization cylinder through the eleventh oil circuit. Then, the pressurization cylinder retracts and the pressurized oil in the rodless chamber flows back to the accumulator along the open sixth oil circuit.

6. The high-precision and high-pressure injection hydraulic system as described in claim 2, characterized in that: The valve module also includes on / off valves V10, V12 and V14; The oil tank is connected to the rodless chamber of the booster cylinder via a switching valve V10 to form a ninth oil circuit; The oil tank is connected to the rodless chamber of the injection cylinder via a switching valve V14 to form a tenth oil circuit; The oil pump is connected to the rod chamber of the booster cylinder through a series of switching valves V12 and servo valves V15 to form the thirteenth oil circuit. During the return hammer phase after the tracking phase, the oil pump supplies oil to the rod chambers of the injection cylinder and the booster cylinder through the first and thirteenth oil circuits, respectively; at the same time, the rodless chambers of the injection cylinder and the booster cylinder return the pressurized oil to the oil tank through the tenth and ninth oil circuits, respectively.

7. The high-precision and high-pressure injection hydraulic system as described in any one of claims 1-6, characterized in that: During the slow injection phase, the oil pump supplies oil to the rodless chamber of the injection cylinder through the connected third oil circuit, and the accumulator supplies oil to the rodless chamber of the injection cylinder through the connected fourth oil circuit; at the same time, the first oil circuit is connected and connected to the third oil circuit to form a differential circuit.

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