A pipe jacking machine hydraulic system and a switching method of load-sensitive, constant-pressure control and unloading modes

Abstract

The present application relates to a kind of hydraulic system of pipe jacking machine and the switching method of load sensing, constant pressure control and unloading mode.The hydraulic system includes: switching valve group, switching valve group includes two-position four-way electromagnetic reversing valve, three-position four-way electromagnetic reversing valve, first damping and second damping, switching valve group is used to control the switching of hydraulic system between load sensing control, constant pressure control and unloading mode;Multi-way valve group, multi-way valve group includes input port and LS port, LS port is communicated load end, LS port is connected to hydraulic system by oil line, for the load pressure of pipe jacking machine to the feedback of hydraulic system;Variable plunger pump, variable plunger pump is connected to LS port by switching valve group, and variable plunger pump is used to automatically adjust output pressure and flow according to the change of LS port load pressure.The present application realizes the efficient switching between load sensing and constant pressure control mode of pipe jacking machine hydraulic system, solves the problem that the pressure of existing pipe jacking machine hydraulic system is insufficient due to along pressure loss.

Description

Technical Field

[0001] This application relates to the field of small-diameter pipe jacking machines, specifically to a hydraulic system for a pipe jacking machine and a method for switching between load-sensitive, constant-pressure control, and unloading modes. Background Technology

[0002] Currently, the hydraulic control of small-diameter pipe jacking machines mainly adopts an open-type variable pump hydraulic system. Based on the control output form and the variable pump process, this type of hydraulic system is divided into load-sensitive and constant-pressure control systems. The load-sensitive control system uses the variable pump as a hydraulic compensator, simultaneously sensing the system's pressure and flow demands and responding instantly. In the constant-pressure control system, if the variable pump pressure does not reach the set value, the variable pump outputs its full displacement to maintain a constant system pressure.

[0003] In existing pipe jacking machines, due to space constraints in the main unit, a rear-mounted power source is typically used, connected to the actuator via long hydraulic pipelines. However, this design results in significant pressure loss along the pipe, making it difficult for the load-sensitive control system to meet actual working pressure requirements, thus reducing equipment safety and efficiency. Summary of the Invention

[0004] In view of this, the present invention provides a hydraulic system for a pipe jacking machine and a method for switching between load-sensitive, constant-pressure control and unloading modes, thereby solving or at least alleviating one or more of the above-mentioned problems and other problems existing in the prior art.

[0005] To achieve the aforementioned objectives, a first aspect of the present invention provides a hydraulic system for a pipe jacking machine, wherein the hydraulic system comprises: The switching valve group includes a two-position four-way solenoid directional valve, a three-position four-way solenoid directional valve, a first damper and a second damper. The switching valve group is used to control the hydraulic system to switch between load-sensitive control, constant pressure control and unloading mode. A multi-way valve group, comprising an input port and an LS port, wherein the LS port is connected to the load device of the pipe jacking machine, and the LS port is connected to the switching valve group via an oil circuit, for feeding back the load pressure of the pipe jacking machine to the hydraulic system; A variable displacement piston pump is connected to the LS port via the switching valve assembly. The variable displacement piston pump is used to automatically adjust the output pressure and flow rate according to the change in load pressure of the LS port.

[0006] In the hydraulic system described above, optionally, the variable displacement piston pump includes a load-sensitive valve, a first variable displacement cylinder, a second variable displacement cylinder, and a pressure shut-off valve. The right end of the load-sensitive valve is connected to the outlet of the variable displacement piston pump, and the left end of the load-sensitive valve is connected to the LS port through the switching valve group, for adjusting the displacement of the variable displacement piston pump according to the pressure feedback of the LS port. The rodless chamber of the first variable displacement cylinder is connected to the outlet, and the rodless chamber of the second variable displacement cylinder is connected to the load-sensitive valve. The pistons of the first and second variable displacement cylinders are both connected to the swashplate of the variable displacement piston pump, and the displacement of the variable displacement piston pump is controlled by adjusting the tilt angle of the swashplate. The pressure shut-off valve adjusts its set pressure through a hard spring to adjust the displacement of the variable displacement piston pump. When the system pressure reaches or exceeds the set pressure, the pressure shut-off valve is used to connect the rodless chamber of the second variable displacement cylinder and the outlet, reducing the displacement of the variable displacement piston pump.

[0007] In the hydraulic system described above, optionally, the left position of the two-position four-way solenoid directional valve is used to feed back the pressure of the LS port to the left end of the load-sensitive valve; the left position of the two-position four-way solenoid directional valve is used to feed back the pressure of the outlet port to the left end of the load-sensitive valve through the pilot-operated relief valve, so as to adjust the displacement of the variable piston pump according to the set pressure of the pilot-operated relief valve.

[0008] In the hydraulic system described above, optionally, the left position of the three-position four-way solenoid directional valve is used to connect the oil outlet and the LS port, and the right position of the three-position four-way solenoid directional valve is used to disconnect the oil outlet from the switching valve group, and the LS port is directly unloaded to the oil tank.

[0009] In the hydraulic system described above, optionally, the variable displacement piston pump includes a constant power control valve to prevent the actual power of the pump from exceeding the rated power. The constant power control valve includes a sleeve connected to the cylinder body of the first variable displacement cylinder. A small piston with a roller at its top is slidably connected inside the sleeve. The bottom end of the small piston is connected to the rodless chamber of the first variable displacement cylinder through an oil passage. The roller presses against one end of a rocker arm of the constant power control valve. The other end of the rocker arm is fixedly connected to an adjustable spring and the constant power control valve.

[0010] To achieve the aforementioned objective, a second aspect of the present invention provides a method for switching between load-sensitive, constant-pressure control, and unloading modes of the hydraulic system described in the first aspect of the present invention. By adjusting the working states of the three-position four-way solenoid directional valve and the two-position four-way solenoid directional valve, the switching between load-sensitive, constant-pressure control, and unloading modes of the hydraulic system is completed.

[0011] In the switching method described above, optionally, when switching to load-sensitive mode: De-energize both the left and right electromagnets of the three-position four-way solenoid valve, so that the three-position four-way solenoid valve returns to the middle position. Check and confirm that the LS port is connected to the left end of the load-sensitive valve.

[0012] In the switching method described above, optionally, when switching to the first constant pressure control mode: De-energize the right-end electromagnet of the three-position four-way solenoid valve, causing the three-position four-way solenoid valve to return from the right position to the middle position. The left electromagnet of the three-position four-way solenoid valve is energized, causing the three-position four-way solenoid valve to switch to the left position working state. Check and confirm that the oil outlet is connected to the LS port through the left position of the three-position four-way solenoid valve; The pressure cut-off valve is adjusted to set pressure. When the system pressure reaches the set value, the pressure cut-off valve is used to adjust the displacement of the variable piston pump to maintain a constant pressure.

[0013] In the switching method described above, optionally, when switching to the second constant pressure control mode: De-energize the right-end electromagnet of the three-position four-way solenoid valve, causing the three-position four-way solenoid valve to return from the right position to the middle position. The left electromagnet of the three-position four-way solenoid valve and the electromagnet of the two-position four-way solenoid valve are simultaneously energized, so that both the three-position four-way solenoid valve and the two-position four-way solenoid valve are switched to the left position working state. The pressure at the oil outlet is fed back to the left end of the load-sensitive valve through a pilot-operated relief valve; According to the set pressure of the pilot-operated relief valve, when the system pressure is less than the set pressure, the variable displacement piston pump operates at its maximum displacement. When the system pressure reaches the set pressure, the pilot-operated relief valve maintains the system pressure at the set pressure.

[0014] In the switching method described above, optionally, when switching to uninstallation mode: The right electromagnet of the three-position four-way solenoid valve is energized, so that the three-position four-way solenoid valve is in the right position working state. The oil outlet is disconnected from the switching valve group, the oil outlet is disconnected from the LS port, and the LS port is directly unloaded to the oil tank.

[0015] This invention solves the problem of insufficient pressure caused by pressure loss along the pipe jacking machine's hydraulic system by achieving efficient switching between load-sensitive and constant-pressure control modes. Through the cooperation of a directional valve assembly and a variable displacement piston pump, the hydraulic system of this invention can quickly switch control modes under different pressure requirements, ensuring stable and accurate pressure output under complex working conditions. Attached Figure Description

[0016] The disclosure of this invention will become more apparent from the accompanying drawings. It should be understood that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings: Figure 1 This is a schematic diagram of one embodiment of the hydraulic system for the pipe jacking machine of the present invention.

[0017] Figure reference numerals: 1-Variable displacement piston pump; 11-Load-sensitive valve; 12-Pressure shut-off valve; 13-First variable displacement cylinder; 14-Second variable displacement cylinder; 15-Outlet port; 16-Constant power control valve; 161-Small piston; 162-Rocker arm; 17-Swashplate; 2-Multi-way valve assembly; 21-Input port; 22-LS port; 3-Switching valve assembly; 31-Two-position four-way solenoid directional valve; 32-Three-position four-way solenoid directional valve; 33-Pilot-operated relief valve; 34-First damper; 35-Second damper. Detailed Implementation

[0018] Referring to the accompanying drawings and specific embodiments, the structure, composition, features, and advantages of a hydraulic system for a pipe jacking machine and a method for switching between load-sensitive, constant-pressure control, and unloading modes according to the present invention will be described by way of example below. However, all descriptions should not be construed as limiting the present invention in any way.

[0019] Furthermore, for any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the various figures, the present invention still allows for any combination or deletion of these technical features or their equivalents without any technical obstacle, and thus these further embodiments according to the present invention should also be considered within the scope of the description herein.

[0020] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0021] It should also be noted that the terms "left" and "right" indicate the orientation or positional relationship based on the relative positional relationship of different valve positions of the hydraulic valves in the hydraulic system shown in the accompanying drawings. They are used only for the convenience of describing this disclosure and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this disclosure.

[0022] Figure 1 This is a schematic diagram of one embodiment of the hydraulic system for the pipe jacking machine of the present invention.

[0023] like Figure 1 As shown, the hydraulic system of the present invention includes a switching valve group 3, a multi-way valve group 2, and a variable displacement piston pump 1. The switching valve group 3 comprises a two-position four-way solenoid directional valve 31, a three-position four-way solenoid directional valve 32, a first damper 34, and a second damper 35. The switching valve group 3 controls the switching of the hydraulic system between load-sensitive control, constant pressure control, and unloading modes. By switching different valve positions, the system can adapt to different working states and requirements, thereby improving the flexibility and efficiency of the hydraulic system. The multi-way valve group 2 includes an input port 21 and an LS port 22. The LS port 22 connects to the load equipment of the pipe jacking machine and is connected to the switching valve group 3 via an oil circuit, serving to provide feedback on the load pressure of the pipe jacking machine to the hydraulic system. The input port 21 is connected to the outlet port 15 of the variable displacement piston pump 1 via a hydraulic pipeline, used to receive the hydraulic oil output by the variable displacement piston pump 1 and distribute it to the various actuators in the system. In this way, the hydraulic oil can flow stably within the system, ensuring the normal operation of the equipment under different working conditions. The variable displacement piston pump 1 is connected to the LS port 22 via the switching valve group 3, and is used to automatically adjust the output pressure and flow rate according to the load pressure changes fed back by the LS port 22.

[0024] The variable displacement piston pump 1 includes a load-sensitive valve 11, a first variable displacement cylinder 13, a second variable displacement cylinder 14, and a pressure shut-off valve 12. The right end of the load-sensitive valve 11 is connected to the outlet 15 of the variable displacement piston pump 1, and the left end is connected to the LS port 22 via a switching valve assembly 3, thereby adjusting the displacement of the variable displacement piston pump 1 based on the pressure feedback from the LS port 22. The rodless chamber of the first variable displacement cylinder 13 is connected to the outlet 15, while the rodless chamber of the second variable displacement cylinder 14 is connected to the load-sensitive valve 11. The pistons of both the first and second variable displacement cylinders 13 are connected to the swashplate 17 of the variable displacement piston pump 1. By adjusting the tilt angle of the swashplate 17, the displacement of the variable displacement piston pump 1 can be precisely controlled. The pressure shut-off valve 12, with its set pressure adjusted by a stiff spring, connects the rodless chamber of the second variable displacement cylinder 14 to the outlet 15 when the system pressure reaches or exceeds the set pressure, thereby reducing the displacement of the variable displacement piston pump 1 and maintaining system pressure stability.

[0025] In the hydraulic system of this invention, the left position of the two-position four-way solenoid directional valve 31 is used to feed back the pressure of the LS port 22 to the left end of the load-sensitive valve 11, or to feed back the pressure of the outlet 15 to the left end of the load-sensitive valve 11 through the pilot-operated relief valve 33. Based on the set pressure of the pilot-operated relief valve 33, the system can dynamically adjust the displacement of the variable displacement piston pump 1 to adapt to different load requirements.

[0026] The three-position four-way solenoid directional valve 32 has multiple operating positions. Its left position is used to connect the oil outlet 15 and the LS port 22 to ensure that the pressure signal can be transmitted correctly. The right position of the three-position four-way solenoid directional valve 32 is used to disconnect the oil outlet 15 from the switching valve group 3 and to directly unload the LS port 22 to the oil tank, thereby realizing the unloading mode of the system.

[0027] The implementation method of the hydraulic system of the present invention will be described below in conjunction with the working process of the hydraulic system.

[0028] When the variable displacement piston pump 1 is not in operation, there is no hydraulic pressure in the system, and the spool of the load-sensitive valve 11 is pushed to the right end by its spring. Since there is no pressure resisting the spring force at the right end of the spool, it remains in the right-end position. In this state, the left position of the load-sensitive valve 11 is engaged. The rodless chamber of the second variable displacement cylinder 14 forms a direct oil passage with the oil tank through the left position of the load-sensitive valve 11, the pressure shut-off valve 12, and the constant power control valve 16. This ensures that the hydraulic oil can flow smoothly back before system startup, preventing hydraulic oil from stagnating in the system and preventing hydraulic shock in the pipeline during system startup.

[0029] In the hydraulic system, the pistons of the first variable cylinder 13 and the second variable cylinder 14 are initially driven by both spring force and hydraulic line pressure. The spring force of the first variable cylinder 13 is greater than that of the second variable cylinder 14. This results in zero line pressure initially, and due to the stronger spring force of the first variable cylinder 13, the swashplate 17 of the variable piston pump 1 is pushed to its maximum tilt angle. This means that after the drive motor of the variable piston pump 1 starts rotating, the variable piston pump 1 can operate at its maximum displacement from the outset. The hydraulic oil in the system is rapidly pressurized and flows to each working unit. At this time, the system can quickly establish the pressure required for operation and immediately provide the necessary flow support, ensuring that the system can quickly enter the working state. In this invention, the design of allowing the variable piston pump 1 to start operating at its maximum displacement ensures that after startup, the system can quickly provide sufficient flow to meet the needs of hydraulic actuators or other driven load devices, especially in situations requiring rapid response or large flow in the initial stage.

[0030] To ensure the safety of the hydraulic system during the initial pressure build-up phase, the drive motor of the variable displacement piston pump 1 can be adjusted to regulate the pressure increase rate through gentle start-up or a gradual increase in motor speed, thus avoiding unnecessary impact on hydraulic lines and other components. Furthermore, when the swashplate 17 is at its maximum tilt angle, although the variable displacement piston pump 1 provides maximum displacement, high pressure has not yet been established in the lines during the initial system startup, resulting in minimal initial impact on the system. As the system pressure gradually builds up, the load-sensitive valve 11 and other control valves begin to participate in the hydraulic system's displacement control to ensure a smooth transition to the operating state.

[0031] To cope with the varying loads generated by the pipe jacking machine under complex working conditions, it is necessary to switch valve group 3 to adopt a load-sensitive mode. The hydraulic system of this invention can switch between load-sensitive, constant pressure control, and unloading modes.

[0032] By adjusting the operating states of the three-position four-way solenoid directional valve 32 and the two-position four-way solenoid directional valve 31, the system can switch between different modes. The implementation method of this switching is described in detail below: When switching to load-sensitive mode, de-energize both the left and right solenoids of the three-position four-way solenoid directional valve 32, returning it to the neutral position, and de-energize the solenoid of the two-position four-way solenoid directional valve 31, making it operate in the right position. Check and confirm that LS port 22 is connected to the left end of load-sensitive valve 11, and feed back the load pressure from LS port 22 to load-sensitive valve 11, thus entering load-sensitive mode. The system pressure sensed by load-sensitive valve 11 will feed back to adjust the pump's displacement to meet the current load requirements. When the load increases, the pump's displacement increases to ensure sufficient hydraulic oil flow; when the load decreases, the pump's displacement decreases accordingly, thus avoiding energy waste.

[0033] When the drive motor of the variable displacement piston pump 1 starts to rotate, the pressure in the hydraulic system increases. The right end of the load-sensitive valve 11 is connected to the output line of the variable displacement piston pump 1, so the pressure at the right end is equal to the output pressure of the variable displacement piston pump 1. The two-position four-way solenoid directional valve 31 is de-energized and pushed to the left end by the spring force. At this time, the directional valve is in the right position, and the LS port 22 of the multi-way valve group 2 is connected to the left end of the load-sensitive valve 11. Therefore, the left end of the load-sensitive valve 11 of the variable displacement piston pump 1 bears the pressure of the LS port 22 and the spring force of its own spring, while the right end bears the pressure of the outlet 15 of the variable displacement piston pump 1. The hydraulic system is in load-sensitive mode at this time.

[0034] The specific implementation of the load-sensitive mode is as follows: When the load increases, the pressure at port 22 of the multi-way valve group 2LS rises. This pressure, combined with the spring force of the valve body, is greater than the pressure at the outlet 15 of the variable displacement piston pump 1 on the right side of the valve body. The force balance of the load-sensitive valve 11 is broken, causing it to slide to the right, with its left position in the working state. In this state, the rodless chamber of the second variable cylinder 14 is connected to the oil tank through the left position of the load-sensitive valve 11, the left position of the pressure shut-off valve 12, and the right position of the constant power control valve 16. Therefore, the oil pressure in the rodless chamber of the second variable cylinder 14 is zero, and its piston only bears the spring force of its own spring. The thrust of the second variable cylinder 14 on the swashplate 17 of the variable displacement piston pump 1 is much smaller than that of the first variable cylinder 13. The first variable cylinder 13 pushes the swashplate 17 to increase its tilt angle, and the displacement of the variable displacement piston pump 1 increases accordingly.

[0035] When the load decreases, the pressure at port 22 of the multi-way valve group 2 drops. The pressure at port 22 on the left side of the load-sensitive valve 11, combined with the spring force of the valve body, is less than the pressure at the outlet 15 of the variable displacement pump 1 on the right side of the valve. This causes the load-sensitive valve 11 to slide to the left, and its right position is in the working state. In this state, the rodless chamber of the second variable cylinder 14 is connected to the outlet 15 of the variable displacement pump 1 through the right position of the load-sensitive valve 11, the left position of the pressure shut-off valve 12, and the right position of the constant power control valve 16. Since the rodless chamber of the first variable cylinder 13 is also connected to the outlet 15 of the variable displacement pump 1, and the piston diameter of the second variable cylinder 14 is larger than that of the first variable cylinder 13, the thrust of the second variable cylinder 14 on the swashplate 17 of the variable displacement pump 1 is greater than that of the first variable cylinder 13. The second variable cylinder 14 pushes the swashplate 17 to reduce its tilt angle, and the displacement of the variable displacement pump 1 decreases accordingly. This prevents the variable pump from outputting too much hydraulic oil and avoids energy waste.

[0036] In actual production, it was found that long-distance hydraulic pipelines can cause significant pressure loss. In this case, a constant pressure mode is required to provide a larger flow rate to the hydraulic system.

[0037] When switching to the first constant pressure control mode, the right-end solenoid of the three-position four-way solenoid directional valve 32 needs to be de-energized, returning it from the right position to the middle position. Then, the left-end solenoid is energized, switching it to the left-end working state. It is then checked and confirmed that the oil outlet 15 is connected to the LS port 22 through the left position of the three-position four-way solenoid directional valve 32. Therefore, the combined pressure of the oil outlet 15 and the LS port 22 acts on the left end of the load-sensitive valve 11. At this time, the left end of the spool of the load-sensitive valve 11 is subjected to the pressure of the oil outlet 15 and the spring force, while the right end only bears the pressure of the oil outlet 15. Therefore, as long as the switching valve group 3 remains in this state, the load-sensitive valve 11 will always remain in the left-end working position. The rodless chamber of the second variable cylinder 14 is connected to the oil tank through the left position of the load-sensitive valve 11 and the left position of the pressure cut-off valve 12, so the oil pressure in the rodless chamber of the second variable cylinder 14 is zero. The first variable cylinder 13 pushes the swashplate 17 of the variable piston pump 1 to increase its tilt angle to the maximum, causing the pump to operate at its maximum displacement. The pressure shut-off valve 12 has a high spring stiffness, and the maximum pressure in the pipeline can be set by adjusting the spring preload. When the load does not reach the set pressure, the variable displacement piston pump 1 operates at its maximum displacement. When the pipeline pressure exceeds the preset pressure, the pressure shut-off valve 12 moves to the left and operates in its right position. By connecting the rodless chamber of the second variable cylinder 14 to the outlet port 15 of the variable displacement piston pump 1, the variable cylinder will push the swashplate 17 of the variable displacement piston pump 1 to reduce its tilt angle, thereby reducing the pump's displacement and stopping the pipeline pressure from rising, thus maintaining the set constant pressure.

[0038] In constant pressure control mode, when the load pressure is low, the variable displacement piston pump 1 operates at its maximum displacement. However, once the load pressure increases, the pump's power increases accordingly. Therefore, a constant power control valve 16 can be used to prevent the pump's actual power from exceeding its rated power, thus protecting the variable displacement piston pump 1. Figure 1As shown, the cylinder body of the first variable cylinder 13 is fixedly connected to a sleeve, inside which a small piston 161 with a roller at its top is slidably connected. The bottom end of the small piston 161 is connected to the rodless chamber of the first variable cylinder 13 via an oil passage, thus the pressure in the rodless chamber of the first variable cylinder 13 acts on the bottom end of the small piston 161. The roller presses against one end of the rocker arm 162 of the constant power control valve 16. The other end of the rocker arm 162 is fixedly connected to the adjustable spring and the right end of the constant power control valve 16. When the pressure at the oil outlet 15 is sufficiently high, the torque of the thrust of the small piston 161 on the rocker arm 162 is greater than the torque of the adjustable spring preload on the rocker arm 162. The rocker arm 162 is pushed and rotates clockwise. Under the action of the return spring, the slide valve of the constant power control valve 16 slides to the right end, and the valve operates in the left position. This connects the rodless chamber of the second variable cylinder 14 to the outlet 15 of the variable piston pump 1 via the left position of the constant power control valve 16. The second variable cylinder 14 pushes the swashplate 17 to reduce its tilt angle, thereby reducing the flow rate of the variable piston pump 1. The constant power control valve 16 limits the pump's output power within a predetermined range by adjusting the angle of the swashplate 17 of the variable piston pump 1. Even when the system requires high flow and high pressure output, the constant power control valve 16 ensures that the pump will not exceed its rated power due to load demands.

[0039] like Figure 1 As shown, the constant power control valve 16 of the hydraulic system of the mining pipe jacking machine of the present invention functions as follows: when the pipeline pressure reaches or exceeds the preset value set by the pressure shut-off valve 12, the pressure shut-off valve 12 acts first, reducing the pump's displacement to prevent further pressure increases. However, if the total power demand of the system exceeds the power capacity of the variable piston pump 1 at this time, the constant power control valve 16 will further limit the pump's displacement by reducing the angle of the swashplate 17 to prevent the pump from overheating or being damaged due to overload. In constant pressure mode, the constant power control valve 16 and the pressure shut-off valve 12 do not work independently; they cooperate with each other. The constant power control valve 16 continuously monitors the output power of the variable piston pump 1 and adjusts it as needed to maintain a safe power level for the system. When the pressure shut-off valve 12 regulates the pressure, the constant power control valve 16 also monitors and responds to changes in the pump's displacement, ensuring that the pump always operates within its rated power range.

[0040] Furthermore, in constant pressure mode, in addition to the pressure shut-off valve 12 and the constant power control valve 16, a flow control valve or pressure relief valve can be added as a multi-layer protection mechanism to improve system safety and efficiency. This will ensure that even under extreme conditions (such as sudden high load or abnormal operation), the system can still maintain within a safe operating range. When the system load suddenly changes, causing the output power of the variable piston pump 1 and the pipeline pressure to rise rapidly, the multi-layer protection mechanism can adjust in stages: first, the pressure shut-off valve 12 quickly responds to the pressure rise; then, the constant power control valve 16 adjusts the pump's displacement to control the power; finally, the pressure relief valve refines the control to ensure a smooth transition for the entire system.

[0041] By installing sensors and feedback loops at key locations in the pipeline, changes in system pressure, flow rate, and power can be monitored in real time. This data can be transmitted to a central control unit (such as a PLC controller) and displayed visually. This not only helps operators better understand the system's operating status but also enables early warning and automatic adjustments for abnormal situations.

[0042] In addition to the first constant pressure control mode, constant pressure control can also be achieved through another adjustment method.

[0043] When switching to the second constant pressure control mode, the right-end solenoid of the three-position four-way solenoid directional valve 32 is de-energized, returning it from the right position to the middle position. Then, the left-end solenoid of the three-position four-way solenoid directional valve 32 and the solenoid of the two-position four-way solenoid directional valve 31 are simultaneously energized, switching both to the left-end working state. The LS port 22 in the system is connected to the oil outlet 15 of the variable piston pump 1, and a pilot-operated relief valve 33 is also connected in this circuit. The pressure at the oil outlet 15 of the variable piston pump 1 first passes through the pilot-operated relief valve 33, and then feeds back to the left end of the load-sensitive valve 11. The pilot-operated relief valve 33 controls the system output pressure by adjusting the pressure. When the actual system pressure is lower than the adjusted pressure of the relief valve 33, the variable piston pump 1 continues to output at full displacement; when the system pressure reaches or exceeds the adjusted value, the pilot-operated relief valve 33 maintains the system pressure at the adjusted pressure. Compared to using only the pressure shut-off valve 12, this mode allows the system to achieve constant pressure output over a wider pressure range. The set pressure of the pilot-operated relief valve 33 can be flexibly adjusted, allowing the system to adapt to different pressure requirements. This design enables the system to provide stable pressure output under more complex working conditions. When the mining pipe jacking machine equipped with the hydraulic system of this invention faces different working conditions, the constant working pressure of the system can be easily adjusted in multiple stages.

[0044] The two constant pressure control modes described above have different characteristics and application scenarios. In the scheme using the pressure shut-off valve 12 to provide constant pressure control, the adjustment range of the pressure shut-off valve 12 is relatively fixed, making it suitable for standard constant pressure scenarios. The scheme using the pilot-operated relief valve 33 to adjust the pressure provides a more flexible constant pressure adjustment range for the hydraulic system of this invention, suitable for applications requiring different pressure levels. Through these two constant pressure control modes, the hydraulic system of this invention can flexibly switch between constant pressure control and load-sensitive control according to specific working conditions, and can adjust the output pressure according to different load conditions, significantly improving the flexibility, efficiency, and safety of the hydraulic system.

[0045] In addition to its high-energy-consuming operating state, the hydraulic system of the mining pipe jacking machine of this invention also has a low-energy-consuming standby or non-operating state. In this situation, the system not only needs to maintain minimal energy consumption but also ensures that it can quickly restore normal operating pressure to meet the needs of the next operation. Therefore, an efficient and easily switchable unloading mode is of great significance to the overall performance of the hydraulic system.

[0046] When switching to unloading mode, the right-hand solenoid of the three-position four-way solenoid directional valve 32 is energized, putting it in the right-hand working state. The outlet 15 is disconnected from the switching valve group 3, blocking the connection between the outlet 15 and the LS port 22, and the LS port 22 is connected to the oil tank through the right-hand position of the directional valve, thus achieving system unloading. Correspondingly, since the left end of the load-sensitive valve 11 is connected to the LS port 22, it is in a state without hydraulic oil. The left end of the load-sensitive pump is only subjected to spring force. This force is less than the pressure at the outlet 15 of the right-hand variable piston pump 1. Therefore, the spool valve of the load-sensitive pump moves to the left, and its right end operates. This causes the rodless chamber of the second variable cylinder 14 to connect to the outlet 15 of the variable piston pump 1. Since the rodless chamber of the first variable cylinder 13 is also connected to the outlet 15 of the variable piston pump 1, the swashplate 17 of the variable piston pump 1 will be pushed by the piston of the second variable cylinder 14, gradually reducing the tilt angle to a minimum, and the pump flow rate to a minimum. When the pump output flow is at its minimum and the load pressure is zero, the pump output pressure also decreases to a lower standby pressure, thus achieving unloading of the hydraulic pump. The unloading mode designed in this invention, through the ingenious combination of the electromagnetic directional valve and the load-sensitive valve 11, allows the variable displacement piston pump 1 to quickly switch to the minimum flow mode when the system does not require high-pressure output. This design not only reduces energy consumption and extends the lifespan of the hydraulic pump and related components, but also avoids the risk of system overpressure or damage due to misoperation or sudden situations.

[0047] The method to restore normal working pressure from unloading mode is as follows: First, the state of switching valve group 3 needs to be changed. The aforementioned load-sensitive mode and two constant pressure control modes can be selected, and the states of three-position four-way solenoid directional valve 32 and two-position four-way solenoid directional valve 31 can be adjusted.

[0048] Taking the load-sensitive mode as an example: De-energizing the electromagnet at the right end of the three-position four-way solenoid directional valve 32 will cause the three-position four-way solenoid directional valve 32 to return from the right-hand position to its initial state. The three-position four-way solenoid directional valve 32 in the neutral position will disconnect the circuit connected to the LS port 22 from the oil tank, restoring the load pressure of the LS port 22 circuit. At this time, the pressure at the LS port 22 at the left end of the load-sensitive valve 11 is restored. This valve can change its position by comparing the sum of the LS port 22 pressure and the spring force with the pressure at the outlet 15 of the variable piston pump 1, thereby adjusting the oil pressure in the rodless chamber of the second variable cylinder 14, and consequently adjusting the tilt angle of the swashplate 17 of the variable piston pump 1, thus affecting the displacement of the variable piston pump 1.

[0049] To revert from unloading mode to constant pressure control mode, the first method is as follows: First, de-energize the right-end solenoid of the three-position four-way solenoid directional valve 32, returning it from the right position to the middle position. Then, energize the left-end solenoid, switching the directional valve to the left position. In the left position, the pressure at the outlet 15 of the variable piston pump 1 is directly connected to the LS port 22 of the multi-way valve group 2 through the left position of the three-position four-way solenoid directional valve 32, and the system's pressure feedback loop returns to normal. Since the pressure at the outlet 15 of the variable piston pump 1 is higher than the system load pressure, the pressure at the outlet 15 replaces the pressure at the LS port 22 and is fed back to the left end of the load-sensitive valve 11. Under the action of the pressure at the outlet 15 and its own spring force, the spool valve of the load-sensitive valve 11 is pushed to the right, operating in the left position. This allows the rodless chamber of the second variable cylinder 14 to connect to the oil tank through the left position of the load-sensitive valve 11 and the left position of the pressure cut-off valve 12, with zero pressure. Since the first variable cylinder 13 acts solely on the swashplate 17, the swashplate 17 tilt angle of the variable piston pump 1 increases to its maximum, and the pump operates at its maximum displacement. When the system pressure reaches the set value of the pressure shut-off valve 12, the pressure shut-off valve 12 begins to adjust, reducing the pump's displacement and maintaining the set constant pressure output.

[0050] The second method to restore from unloading mode to constant pressure control mode is as follows: De-energize the solenoid on the right end of the three-position four-way solenoid directional valve 32, returning it from the right position to the middle position, and then energize the solenoid on the left end, causing the directional valve to switch to the left position. Simultaneously, energize the solenoid on the two-position four-way solenoid directional valve 31, switching it to the left position. In this state, LS port 22 connects to oil outlet 15, the pipeline pressure is restored, and the pressure at oil outlet 15 is fed back to the left end of the load-sensitive valve 11 via the pilot-operated relief valve 33. The pilot-operated relief valve 33 sets the pressure to control the output pressure of the system. The spool valve of the load-sensitive valve 11 always remains in the left position, and the variable displacement piston pump 1 maintains maximum displacement output. When the system pressure reaches the set pressure of the relief valve, the relief valve begins to adjust, maintaining the system at the set constant pressure.

[0051] Furthermore, a first damper 34 can be installed on the connection path between LS port 22 and switching valve group 3 to buffer the load pressure signal transmitted from LS port 22 to switching valve group 33. A second damper 35 can also be installed on the connection path between oil outlet 15 and switching valve group 3 to buffer the oil outlet pressure signal transmitted from oil outlet 15 to switching valve group 33. Installing the first damper 34 and the second damper 35 can effectively mitigate load pressure fluctuations, reduce hydraulic system instability caused by rapid load changes, reduce the impact of pressure fluctuations on the system, and thus extend the service life of hydraulic components.

[0052] This invention employs a two-position four-way solenoid directional valve 31 and a three-position four-way solenoid directional valve 32 to achieve one-button switching between a constant pressure control system and a load-sensitive control system in the hydraulic system. When there is no need for high-pressure output or holding, the system can be selected to operate in a load-sensitive mode; while when a constant pressure output is required, instantaneous switching can be achieved by energizing the solenoid valves. Furthermore, the system can preset multiple switchable pressure levels through the adjustment of the pilot-operated relief valve 33 to meet pressure output requirements under complex operating conditions.

[0053] Specifically, when the left electromagnet of the three-position four-way solenoid directional valve 32 is energized, the system switches to the first constant pressure control mode set by the pressure shut-off valve 12; when the left electromagnet of the three-position four-way solenoid directional valve 32 and the two-position four-way solenoid directional valve 31 are energized simultaneously, the system switches to the second constant pressure control mode set by the pilot-operated relief valve 33, and this set pressure is adjustable; when it is necessary to enter the standby state or unloading mode, the system can achieve the low-pressure standby state of the variable pump 1 by operating the solenoid valve to switch; when the control valve group 3 does not operate, the system is in the load-sensitive control mode.

[0054] This invention achieves a high degree of integration between electrical and hydraulic systems by replacing traditional manual valves with solenoid valve assemblies. This solves the problem of inconvenient manual operation in certain confined spaces, significantly reduces the risks caused by human error, and improves the safety and intelligence of equipment operation. The integrated solenoid valve assembly design not only simplifies the structure of the hydraulic system, reduces installation space requirements and equipment size, but also meets the need for hydraulic pump 1 to flexibly switch between constant pressure output and load-sensitive control output at different pressure levels.

[0055] This invention realizes a method for switching between load-sensitive and multi-stage constant pressure control in the hydraulic system of a pipe jacking machine. Through integrated automatic control of the electromagnetic directional valve group 3, it achieves efficient switching between the load-sensitive system and multiple constant pressure outputs. This control method not only replaces traditional manual valve operation but also improves the system's automation and intelligence levels.

[0056] The technical scope of this invention is not limited to the contents of the above specification. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the scope of this invention.

Claims

1. A hydraulic system for a pipe jacking machine, characterized in that, The hydraulic system includes: The switching valve group (3) includes a two-position four-way solenoid directional valve (31), a three-position four-way solenoid directional valve (32), a first damper (34), and a second damper (35). The switching valve group (3) is used to control the hydraulic system to switch between load-sensitive control, constant pressure control, and unloading mode. A multi-way valve group (2) includes an input port (21) and an LS port (22). The LS port (22) is connected to the load device of the pipe jacking machine. The LS port (22) is connected to the switching valve group (3) through an oil circuit and is used to feed back the load pressure of the pipe jacking machine to the hydraulic system. A variable displacement piston pump (1) includes a load-sensitive valve (11), a first variable displacement cylinder (13), a second variable displacement cylinder (14), and a pressure shut-off valve (12). The right end of the load-sensitive valve (11) is connected to the oil outlet (15) of the variable displacement piston pump (1), and the left end of the load-sensitive valve (11) is connected to the LS port (22) through the switching valve group (3), for adjusting the displacement of the variable displacement piston pump (1) according to the pressure feedback of the LS port (22); the rodless chamber of the first variable displacement cylinder (13) is connected to the oil outlet (15), and the second variable displacement cylinder (14) is connected to the oil outlet (15). The rodless chamber is connected to the load-sensitive valve (11). The pistons of the first variable cylinder (13) and the second variable cylinder (14) are both connected to the swashplate (17) of the variable piston pump (1). The displacement of the variable piston pump (1) is controlled by adjusting the tilt angle of the swashplate (17). The pressure shut-off valve (12) adjusts its set pressure through a hard spring to adjust the displacement of the variable piston pump (1). When the system pressure reaches or exceeds the set pressure, the pressure shut-off valve (12) is used to connect the rodless chamber of the second variable cylinder (14) and the oil outlet (15) to reduce the displacement of the variable piston pump (1). The left position of the two-position four-way solenoid directional valve (31) is used to feed back the pressure of the LS port (22) to the left end of the load-sensitive valve (11); the left position of the two-position four-way solenoid directional valve (31) is used to feed back the pressure of the oil outlet (15) to the left end of the load-sensitive valve (11) through the pilot-operated relief valve (33) so as to adjust the displacement of the variable piston pump (1) according to the set pressure of the pilot-operated relief valve (33).

2. The hydraulic system for a pipe jacking machine as described in claim 1, characterized in that, The left position of the three-position four-way solenoid directional valve (32) is used to connect the oil outlet (15) and the LS port (22), and the right position of the three-position four-way solenoid directional valve (32) is used to disconnect the oil outlet (15) from the switching valve group (3), and the LS port (22) is directly unloaded to the oil tank.

3. The hydraulic system for a pipe jacking machine as described in claim 2, characterized in that, The variable displacement piston pump (1) includes a constant power control valve (16) to prevent the actual power of the pump from exceeding the rated power. The constant power control valve (16) includes a sleeve connected to the cylinder body of the first variable displacement cylinder (13). A small piston (161) with a roller at the top is slidably connected inside the sleeve. The bottom end of the small piston (161) is connected to the rodless chamber of the first variable displacement cylinder (13) through an oil passage. The roller presses against one end of the rocker arm (162) of the constant power control valve (16). The other end of the rocker arm (162) is fixedly connected to the adjustable spring and the constant power control valve (16).

4. A method for switching between load-sensitive, constant-pressure control, and unloading modes in the hydraulic system of a pipe jacking machine as described in claim 2 or 3, characterized in that, By adjusting the working states of the three-position four-way solenoid directional valve (32) and the two-position four-way solenoid directional valve (31), the switching between load-sensitive, constant-pressure control and unloading modes of the hydraulic system can be completed.

5. The switching method as described in claim 4, characterized in that, When switching to load-sensitive mode: The left and right electromagnets of the three-position four-way solenoid valve (32) are de-energized, so that the three-position four-way solenoid valve (32) returns to the middle position. Check and confirm that the LS port (22) is connected to the left end of the load-sensitive valve (11).

6. The switching method as described in claim 4, characterized in that, When switching to the first constant pressure control mode: The right-end electromagnet of the three-position four-way solenoid valve (32) is de-energized, so that the three-position four-way solenoid valve (32) returns from the right position to the middle position; The left electromagnet of the three-position four-way solenoid valve (32) is energized, so that the three-position four-way solenoid valve (32) is switched to the left position working state. Check and confirm that the oil outlet (15) is connected to the LS port (22) through the left position of the three-position four-way solenoid directional valve (32); Adjust the set pressure of the pressure shut-off valve (12). When the system pressure reaches the set value, the pressure shut-off valve (12) is used to adjust the displacement of the variable piston pump (1) to maintain a constant pressure.

7. The switching method as described in claim 4, characterized in that, When switching to the second constant pressure control mode: The right-end electromagnet of the three-position four-way solenoid valve (32) is de-energized, so that the three-position four-way solenoid valve (32) returns from the right position to the middle position; The left electromagnet of the three-position four-way solenoid valve (32) and the electromagnet of the two-position four-way solenoid valve (31) are simultaneously energized, so that the three-position four-way solenoid valve (32) and the two-position four-way solenoid valve (31) are both switched to the left position working state. The pressure at the oil outlet (15) is fed back to the left end of the load-sensitive valve (11) through the pilot-operated relief valve (33); According to the set pressure of the pilot-operated relief valve (33), when the system pressure is less than the set pressure, the variable displacement piston pump (1) operates at the maximum displacement, and when the system pressure reaches the set pressure, the pilot-operated relief valve (33) maintains the system pressure at the set pressure.

8. The switching method as described in claim 4, characterized in that, When switching to uninstall mode: The right electromagnet of the three-position four-way solenoid valve (32) is energized, so that the three-position four-way solenoid valve (32) is in the right position working state. The oil outlet (15) is disconnected from the switching valve group (3), the oil outlet (15) is disconnected from the LS port (22), and the LS port (22) is directly unloaded to the oil tank.

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