Variable displacement pump load sensing and constant pressure switching control system and control method

Abstract

The application discloses a variable pump load-sensitive and constant-pressure switching control system and a control method, which comprises a multi-way valve and a switching valve group; the switching valve group comprises a reversing valve, a first hydraulic control check valve and a shuttle valve; the application controls the on-off of the first hydraulic control check valve through the switching of the working position of the reversing valve, so that the switching of the constant-pressure and load-sensitive working modes is realized. The control method of the application switches the working mode of the variable pump through the reversing valve; during the switching of the working mode of the pump, the variable pump can continuously maintain the corresponding working state by only switching the handle of the reversing valve to the corresponding working position; specifically, when the reversing valve is switched to the upper position once, the variable pump is in the constant-pressure working mode; when the reversing valve is switched to the lower position once, the variable pump is in the load-sensitive working mode; only by operating the handle of the reversing valve, the switching of the working mode of the variable pump can be realized.

Description

Technical Field

[0001] This invention relates to the field of pump control technology, specifically to a variable pump load-sensitive and constant pressure switching control system and control method. Background Technology

[0002] Currently, open variable pump hydraulic systems commonly fall into two categories based on pump control methods: load-sensitive control hydraulic systems, where the hydraulic pump output pressure is related to the load force, and constant-pressure control hydraulic systems, where the hydraulic pump output pressure is constant. In the load-sensitive control system, the variable pump acts as a hydraulic compensator, simultaneously sensing the system's pressure and flow demands, enabling the piston pump to respond correctly to changes in flow and pressure requirements. In the constant-pressure control system, when the output pressure is lower than the set constant pressure, the variable pump outputs pressure oil at full displacement. When the output oil pressure reaches the set pressure, it automatically adjusts the pump flow rate to ensure constant pressure and meet system requirements.

[0003] The problem with existing technologies is that, for existing open variable pump systems, the switching between constant pressure control and load-sensitive control is usually achieved by solenoid valve control, which requires high technical difficulty. In situations where electrical control is not involved, it cannot meet the multi-functional needs of variable pumps, is difficult to apply to various complex working conditions, and results in a poor user experience.

[0004] In summary, there is an urgent need for a variable pump load-sensitive and constant-pressure switching control system and method to solve the problem of switching between constant-pressure and load-sensitive operating modes of variable pumps by electronic control in the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a variable pump load-sensitive and constant-pressure switching control system and method to solve the problem of relying on electronic control to achieve the switching between constant-pressure and load-sensitive operating modes of variable pumps in the prior art. The specific technical solution is as follows:

[0006] A variable pump load-sensitive and constant pressure switching control system includes a multi-way valve and a switching valve group; the inlet P2 of the multi-way valve is connected to the outlet P1 of the variable pump (3), and the feedback port LS of the multi-way valve is connected to the switching valve group; the switching valve group includes a directional valve, a first hydraulic check valve, and a shuttle valve; the P port of the directional valve is connected to the outlet P1 of the variable pump, and the B port of the directional valve is connected to the control chamber of the first hydraulic check valve; the inlet and outlet P1 of the first hydraulic check valve are connected, and the outlet of the first hydraulic check valve is connected to the first inlet of the shuttle valve; the second inlet of the shuttle valve is connected to the feedback port LS of the multi-way valve, and the outlet of the shuttle valve is connected to the variable mechanism of the variable pump.

[0007] In the preferred embodiment of the above technical solution, the switching valve group also includes a relief valve; the oil inlet of the relief valve is connected to the oil outlet of the first hydraulic check valve, and the oil outlet of the relief valve is connected to the oil tank.

[0008] In the preferred embodiment of the above technical solution, a check valve is provided between the B port of the reversing valve and the control chamber of the first hydraulic check valve; the permissible flow direction of the check valve is from the B port to the control chamber of the first hydraulic check valve.

[0009] In the preferred embodiment of the above technical solution, the oil outlet of the first hydraulic check valve is connected to the control chamber of the first hydraulic check valve.

[0010] In the preferred embodiment of the above technical solution, a first damping is provided between the oil outlet of the first hydraulic check valve and the control chamber of the first hydraulic check valve.

[0011] In the preferred embodiment of the above technical solution, a second damping is provided between the oil outlet of the first hydraulic check valve and the oil tank; a third damping is provided between the oil outlet of the first hydraulic check valve and the first oil inlet of the shuttle valve.

[0012] In the preferred embodiment of the above technical solution, the damping forces of the first damper and the third damper are both less than the damping force of the second damper.

[0013] In the preferred embodiment of the above technical solution, the directional valve is a three-position four-way directional valve with self-resetting function.

[0014] In a preferred embodiment of the above technical solution, the switching valve group further includes a second hydraulically controlled check valve; the A port of the reversing valve is connected to the control chamber of the second hydraulically controlled check valve; the oil inlet of the second hydraulically controlled check valve is connected to the control chamber of the first hydraulically controlled check valve; and the oil outlet of the second hydraulically controlled check valve is connected to the oil tank.

[0015] A variable pump load-sensitive and constant-pressure switching control method, employing the aforementioned variable pump load-sensitive and constant-pressure switching control system, is detailed below:

[0016] Initial state: The directional valve is in the neutral position, and the oil enters the multi-way valve from the outlet P1. The control oil of the directional valve's P port is taken from the outlet P1. At this time, the first hydraulic check valve is closed, and the pressure oil at the outlet P1 cannot be fed back to the variable mechanism. However, the oil at the feedback port LS of the multi-way valve can be fed back to the variable mechanism through the outlet of the shuttle valve. At this time, the variable pump is in load-sensitive mode.

[0017] When the reversing valve switches to the upper position, the oil at the outlet P1 enters the control chamber of the first hydraulic check valve, causing the first hydraulic check valve to open. The oil at the outlet P1 reaches the shuttle valve through the outlet of the first hydraulic check valve and is fed back to the variable mechanism from the outlet of the shuttle valve. At this time, the variable pump is in constant pressure mode.

[0018] When the directional valve switches to the lower position, the oil at the outlet P1 enters the control chamber of the second hydraulic check valve through port A of the directional valve, causing the second hydraulic check valve to open. The oil in the control chamber of the first hydraulic check valve is discharged through the second hydraulic check valve, and the first hydraulic check valve closes. At this time, the variable pump switches from constant pressure mode to load sensitive mode.

[0019] The application of the technical solution of the present invention has the following beneficial effects:

[0020] (1) The variable pump load-sensitive and constant pressure switching control system of the present invention includes a multi-way valve and a switching valve group; the switching valve group includes a directional valve, a first hydraulically controlled check valve, and a shuttle valve; the present invention controls the opening and closing of the first hydraulically controlled check valve by switching the position of the directional valve to realize the switching between constant pressure and load-sensitive working modes. The switching principle is as follows: when the directional valve is in the neutral position, the oil of the variable pump enters the multi-way valve from the oil outlet P1. At this time, the first hydraulically controlled check valve is in the closed state, and the oil outlet of the variable pump cannot be fed back to the variable mechanism of the variable pump. However, the oil from the feedback oil port LS of the multi-way valve can be fed back to the variable mechanism through the oil outlet of the shuttle valve. At this time, it is in the load-sensitive mode; when the directional valve is switched to the upper position, the P port and B port of the directional valve are connected, so that the first hydraulically controlled check valve is opened, and the oil outlet of the variable pump reaches the shuttle valve through the first hydraulically controlled check valve. The second inlet, since the first inlet of the shuttle valve is the load pressure oil fed back from the multi-way valve, according to the working principle of the load-sensitive system, the load feedback pressure will be less than the outlet oil pressure. Therefore, the oil at outlet P1 can be fed back to the variable mechanism through the outlet of the shuttle valve, and at this time it is in constant pressure mode. That is, the present invention uses a reversing valve and hydraulic control to achieve mode switching, which has the following advantages: a) Reduce system cost and improve system reliability. The present invention replaces the previous electronic control working mode with hydraulic control. In some hydraulic systems that do not involve electronic control schemes, system cost can be saved. At the same time, replacing electronic control with hydraulic control improves reliability; b) Improve the system's adaptability to working conditions and working efficiency. The present invention can switch the pump's working mode to load-sensitive and constant pressure according to the actual working conditions. The system has a stronger ability to adapt to working conditions and higher efficiency.

[0021] (2) In this invention, when the system pressure increases to the pressure set by the overflow valve, the control oil (i.e. the oil coming out of the outlet of the first hydraulic check valve) overflows from the overflow valve to the oil tank, so that the pressure of the feedback oil circuit will not increase with the increase of the pump (i.e., variable pump) outlet pressure, thus protecting the system safety.

[0022] (3) In this invention, the function of the check valve is to ensure that after the first hydraulic check valve is opened, the reversing valve returns to the neutral position, and the pressure oil in the control chamber of the first hydraulic check valve will not be leaked out through the reversing valve, so that the first hydraulic check valve can remain open after it is opened.

[0023] (4) In this invention, the oil outlet of the first hydraulic control check valve is connected to the control chamber of the first hydraulic control check valve. When the pump is switched to constant pressure working mode, the reversing valve returns to the neutral position and the check valve is closed. At this time, the outlet oil of the first hydraulic control check valve enters its control chamber, so that the first hydraulic control check valve continues to be open. Therefore, the pressure fed back to the variable pump (specifically the variable mechanism) is still the pump outlet pressure, and the pump can continue to maintain a constant pressure state.

[0024] (5) In this invention, the function of the first damping is to ensure that when the first hydraulic control check valve is not open, the control oil from the check valve can first reach the control chamber of the first hydraulic control check valve to open the valve core. At the same time, it ensures that when the outlet pressure of the first hydraulic control check valve fluctuates after it is opened, the pressure fed back to the control chamber of the first hydraulic control check valve will not fluctuate significantly, thus maintaining the stable opening state of the first hydraulic control check valve.

[0025] (6) In this invention, the function of the second damper is to ensure that the pressure oil of the constant pressure feedback and the oil in the control chamber of the first hydraulic control check valve can be released when the variable pump stops, so that the first hydraulic control check valve can be closed and the pump can be prevented from starting in constant pressure mode next time.

[0026] (7) In this invention, the function of the third damper is to improve the pressure stability of the constant pressure feedback control oil circuit and avoid frequent fluctuations in control oil pressure, which would cause instability in system pressure.

[0027] (8) In this invention, when the reversing valve is switched from the middle position to the lower position (i.e., the right position), that is, from the constant pressure mode to the load sensitive mode, the second hydraulic control check valve can quickly release the pressure oil of the constant pressure feedback and the oil in the control chamber of the first hydraulic control check valve, so that the first hydraulic control check valve can be closed quickly.

[0028] (9) The control method of the present invention adopts the variable pump load sensitive and constant pressure switching control system. The working mode of the variable pump is switched by the reversing valve. During the process of switching the pump working mode, it is only necessary to switch it to the corresponding working position once, so that the variable pump can continuously maintain the corresponding working state. Specifically, when the reversing valve is switched to the upper position once, the variable pump is in the constant pressure working mode, and when the reversing valve is switched to the lower position once, the variable pump is in the load sensitive working mode. The operation is simple and flexible. The switching of the variable pump working mode can be realized by simply operating the handle of the reversing valve once.

[0029] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] In the attached diagram:

[0032] Figure 1 This is a schematic diagram of the variable pump load-sensitive and constant pressure switching control system in this embodiment;

[0033] Figure 2 yes Figure 1 Schematic diagram of the switching valve assembly;

[0034] Among them, 1. multi-way valve; 2. switching valve group; 2.1 directional valve; 2.2 first hydraulically controlled check valve; 2.3 shuttle valve; 2.31, oil outlet of shuttle valve; 2.4 relief valve; 2.5 check valve; 2.6 first damper; 2.7 second damper; 2.8 third damper; 2.9 second hydraulically controlled check valve; 3. variable pump; 3.1 variable mechanism; 3.1a, control oil port of variable mechanism. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0036] Example:

[0037] This embodiment discloses a variable pump load-sensitive and constant-pressure switching control system. This switching control system can be used to switch the variable pump 3 between load-sensitive and constant-pressure operating modes. The switching control system in this embodiment is mainly described in two parts: the first part describes the connection relationships between the components of the switching control system; the second part describes the specific function of each component, such as... Figures 1 to 2 As shown, the details are as follows:

[0038] Part One:

[0039] The switching control system includes a multi-way valve 1 (i.e., a load-sensitive multi-way valve) and a switching valve group 2; the switching valve group 2 includes a directional valve 2.1, a first hydraulically controlled check valve 2.2, a shuttle valve 2.3, an overflow valve 2.4, a check valve 2.5, a first damper 2.6, a second damper 2.7, a third damper 2.8, and a second hydraulically controlled check valve 2.9;

[0040] The inlet P2 of the multi-way valve 1 is connected to the outlet P1 of the variable pump 3. The feedback port LS of the multi-way valve 1 is connected to the shuttle valve 2.3 of the switching valve group 2. Specifically, the feedback port LS is connected to the second inlet of the shuttle valve 2.3, that is, the feedback port LS is connected to the left chamber of the shuttle valve 2.3. The oil at the outlet P1 of the variable pump 3 can enter the multi-way valve 1 through the inlet P2. Preferably, the R outlet of the multi-way valve 1 is connected to the oil tank.

[0041] The reversing valve 2.1 is a three-position four-way reversing valve 2.1, specifically a three-position four-way reversing valve 2.1 with a self-resetting function. The working position of the reversing valve 2.1 can be switched by operating its handle. The reversing valve 2.1 is provided with ports P, T, A, and B. Port P is connected to the oil outlet P1 of the variable pump 3, specifically connecting between the oil outlet P1 and the oil inlet P2. Port T is connected to the oil tank. Port A is connected to the control chamber of the second hydraulic check valve 2.9. Port B is connected to the oil inlet of the check valve 2.5. In this embodiment, the reversing valve is a Y-type three-position four-way reversing valve.

[0042] The inlet of the first hydraulic check valve 2.2 is connected to the outlet P1 of the variable pump 3. Specifically, the inlet of the first hydraulic check valve 2.2 is connected between the outlet P1 and the P port. The outlet of the first hydraulic check valve 2.2 is connected to the control chamber of the first hydraulic check valve 2.2, the oil tank, and the first inlet (i.e., the right chamber) of the shuttle valve 2.3. In this embodiment, preferably, a first damping 2.6 is provided between the outlet of the first hydraulic check valve 2.2 and the control chamber of the first hydraulic check valve 2.2, a second damping 2.7 is provided between the outlet of the first hydraulic check valve 2.2 and the oil tank, and a third damping 2.8 is provided between the outlet of the first hydraulic check valve 2.2 and the first inlet of the shuttle valve 2.3.

[0043] The damping forces of the first damper 2.6 and the third damper 2.8 are both less than the damping force of the second damper 2.7, which can ensure the normal operation of the system. For example, the inner diameter of the damping orifice of the first damper 2.6 and the third damper 2.8 is D1, and the inner diameter of the damping orifice of the second damper 2.7 is D2, where D2 is 3-10 times D1.

[0044] The shuttle valve 2.3 includes a first oil inlet, a second oil inlet, and an oil outlet. The first oil inlet is connected to the right chamber of the shuttle valve 2.3, and the second oil inlet is connected to the left chamber of the shuttle valve 2.3. A third damper 2.8 is disposed between the first oil inlet and the oil outlet of the first hydraulic check valve 2.2. The second oil inlet is connected to the feedback oil port LS of the multi-way valve 1. The oil outlet 2.31 of the shuttle valve is connected to the variable mechanism 3.1 of the variable pump 3 (specifically, to the control oil port 3.1a of the variable mechanism). The oil from the oil outlet 2.31 of the shuttle valve is fed back to the control oil port 3.1a of the variable mechanism, thereby adjusting the output oil of the variable pump 3. The variable mechanism 3.1 adjusts the output flow rate according to the oil from the oil outlet of the shuttle valve 2.3, as per existing technology, and will not be elaborated further in this embodiment.

[0045] The oil inlet of the overflow valve 2.4 is connected to the oil outlet of the first hydraulic check valve 2.2. Specifically, the oil inlet of the overflow valve 2.4 is connected between the first oil inlet of the shuttle valve 2.3 and the third damper 2.8. The oil outlet of the overflow valve 2.4 is connected to the oil tank.

[0046] The one-way valve 2.5 is located between the control chamber of the first hydraulically controlled one-way valve 2.2 and the B port of the reversing valve 2.1. The permissible flow direction of the one-way valve 2.5 is from the B port to the control chamber of the first hydraulically controlled one-way valve 2.2.

[0047] The inlet of the second hydraulic check valve 2.9 is connected to the control chamber of the first hydraulic check valve 2.2. Specifically, the inlet of the second hydraulic check valve 2.9 is connected between the control chamber of the first hydraulic check valve 2.2 and the outlet of the check valve 2.5. The outlet of the second hydraulic check valve 2.9 is connected to the oil tank. When oil enters the control chamber of the second hydraulic check valve 2.9 through port A of the reversing valve 2.1, the second hydraulic check valve 2.9 is activated. In this embodiment, the first hydraulic check valve 2.2 and the second hydraulic check valve 2.9 can also be replaced by two-position two-way hydraulic logic valves.

[0048] Part Two:

[0049] Multi-way valve 1 controls the direction of oil flow and simultaneously feeds back the oil (i.e., the LS signal) from the feedback port LS to the switching valve group 2. In other words, multi-way valve 1 has a load feedback function.

[0050] The directional valve 2.1, in conjunction with the check valve 2.5 and the second hydraulically controlled check valve 2.9, can control the opening and closing of the first hydraulically controlled check valve 2.2. The directional valve 2.1 also has a self-resetting function; that is, the function of the directional valve 2.1 is to switch the operating mode of the variable pump 3. During the pump operating mode switching process, simply switching it to the corresponding operating position will allow the variable pump 3 to continuously maintain the corresponding operating state. Specifically, when the directional valve 2.1 switches to the upward position, the variable pump 3 is in constant pressure operating mode; when the directional valve 2.1 switches to the downward position, the variable pump 3 is in load-sensitive operating mode.

[0051] The first hydraulic check valve 2.2 controls the opening and closing of the constant pressure feedback signal oil circuit. When it is open, the pressure oil signal at the outlet P1 can be fed back to the variable mechanism 3.1 of the variable pump 3, enabling the variable pump 3 to achieve constant pressure control. When it is closed, the pressure oil signal at the outlet P1 cannot be fed back to the variable mechanism 3.1 of the variable pump 3, and the constant pressure control fails.

[0052] The function of shuttle valve 2.3 is to select the control oil signal fed back to variable pump 3. When the first hydraulic check valve 2.2 is open, it will feed back the pressure oil signal from the outlet of variable pump 3 to variable mechanism 3.1 to achieve constant pressure control. When the first hydraulic check valve 2.2 is closed, it will feed back the oil from the feedback port LS of multi-way valve 1 to variable mechanism 3.1 to achieve load-sensitive control.

[0053] The function of relief valve 2.4 is to limit the control oil pressure of constant pressure feedback, ensuring that the system pressure does not exceed the set value (the set value is selected according to the actual situation), and protecting the system safety.

[0054] The first damper 2.6 serves to ensure that when the first hydraulic check valve 2.2 is not open, the control oil coming from the check valve 2.5 can first reach the control chamber of the first hydraulic check valve 2.2 to open the valve core. At the same time, it ensures that when the outlet pressure of the first hydraulic check valve 2.2 fluctuates after it is opened, the pressure fed back to the control chamber of the first hydraulic check valve 2.2 will not fluctuate significantly, thus maintaining the stable opening state of the first hydraulic check valve 2.2.

[0055] The second damper 2.7 is designed to ensure that when the variable pump 3 stops, the pressure oil from the constant pressure feedback and the oil in the control chamber of the first hydraulic check valve 2.2 can be released, so that the first hydraulic check valve 2.2 can be closed, preventing the pump from starting in constant pressure mode next time.

[0056] The third damping element, 2.8, is used to improve the pressure stability of the constant pressure feedback control oil circuit and prevent frequent fluctuations in control oil pressure, which could lead to system pressure instability.

[0057] The second hydraulic check valve 2.9 is designed to ensure that when the variable pump 3 switches from constant pressure mode to load-sensitive mode, the pressure oil from the constant pressure feedback and the oil in the control chamber of the first hydraulic check valve 2.2 can be quickly released, so that the first hydraulic check valve 2.2 can be closed.

[0058] In this embodiment, a self-resetting three-position four-way directional valve 2.1 is used in the switching control system with load sensitivity and pressure cut-off functions. By simply moving the handle and cooperating with other valve structures in the switching valve group 2, the working mode of the variable pump 3 can be freely switched between load sensitivity and constant pressure. This working mode can be maintained after the handle returns to the neutral position. At the same time, when the variable pump 3 stops in constant pressure mode, it can automatically switch to load sensitivity mode to avoid the prime mover starting under load next time. This protects the hydraulic components, improves the safety performance of the system, reduces the system heat generation power, and saves energy.

[0059] This embodiment also discloses a load-sensitive and constant-pressure switching control method for a variable pump 3, which employs the aforementioned variable pump load-sensitive and constant-pressure switching control system, as detailed below:

[0060] Initial state (i.e., the operating position of directional valve 2.1 is neutral):

[0061] When the variable pump 3 is started in the initial state, the oil enters the multi-way valve 1 from the outlet P1. The P port of the directional valve 2.1 controls the oil to be taken from the outlet P1. Since the directional valve 2.1 has a self-resetting function, it is in the neutral position in the initial state. At this time, the first hydraulic check valve 2.2 is in the closed state (non-conducting state). The pressure oil at the outlet P1 cannot be fed back to the variable mechanism 3.1 of the variable pump 3. However, the oil at the feedback port LS of the multi-way valve 1 (i.e., the LS signal) can be fed back to the control port 3.1a of the variable mechanism through the outlet 2.31 of the shuttle valve. At this time, the variable pump 3 is in the load sensitive mode.

[0062] When the directional valve 2.1 is switched to the upper position (i.e., the left position):

[0063] The oil from outlet P1 enters the control chamber of the first hydraulically controlled check valve 2.2 through check valve 2.5. Due to the presence of the first damper 2.6, the pressure in the control chamber of the first hydraulically controlled check valve 2.2 can be established, thereby opening the first hydraulically controlled check valve 2.2. Then, the oil from outlet P1 passes through the first hydraulically controlled check valve 2.2 and is filtered by the third damper 2.8 before reaching the first inlet of shuttle valve 2.3 (i.e., the right chamber of shuttle valve 2.3). Since the second inlet of shuttle valve 2.3 (i.e., the left chamber) is the load pressure oil fed back from the feedback port LS of multi-way valve 1, according to the working principle of the load-sensitive system, the load feedback pressure will be less than the pump outlet (i.e., the pressure at outlet P1) pressure. Therefore, the oil from outlet P1 of variable pump 3 is fed back to the variable mechanism 3.1 of variable pump 3 through outlet 2.31 of shuttle valve. The variable mechanism 3.1 operates according to the feedback.

[0064] Preferably, 1. When the variable pump 3 is in constant pressure mode, when the system pressure increases to the pressure set by the overflow valve 2.4, the control oil overflows from the overflow valve 2.4 to the oil tank, so that the pressure of the feedback oil circuit will not increase with the pressure of the oil outlet P1, thus protecting the system safety; 2. When the variable pump 3 is switched to constant pressure working mode, the reversing valve 2.1 returns to the neutral position, and the check valve 2.5 closes. Since the second hydraulic check valve 2.9 is always closed and the second damping 2.7 is applied, the oil at the outlet of the first hydraulic check valve 2.2 enters its control chamber through the first damping 2.6, so that the first hydraulic check valve 2.2 continues to be open. Therefore, the pressure fed back to the variable mechanism 3.1 is still the pressure of the oil outlet P1, and the variable pump 3 can continue to maintain constant pressure mode;

[0065] When the directional valve 2.1 is switched to the lower position (i.e., the right position):

[0066] The control oil from outlet P1 enters the control chamber of the second hydraulic check valve 2.9 through port A of directional valve 2.1, causing the second hydraulic check valve 2.9 to open. The oil in the control chamber of the first hydraulic check valve 2.2 and the oil outlet of the first hydraulic check valve 2.2 can be discharged through the second hydraulic check valve 2.9, thereby causing the first hydraulic check valve 2.2 to close. At this time, the pressure oil fed back to the variable mechanism 3.1 is the oil from the feedback port LS of the multi-way valve 1, that is, the variable pump 3 switches to the load sensitive mode.

[0067] When the variable pump 3 stops in constant pressure mode, the pressure oil in the control chamber of the first hydraulic check valve 2.2 will be released through the second damper 2.7, the first hydraulic check valve 2.2 will close, the variable pump 3 will return to the load sensitive mode, and avoid starting in constant pressure mode next time, thus protecting the system and component safety.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A variable displacement pump load sensing and constant pressure switching control system characterized by, The switching valve group (2) comprises a reversing valve (2.1), a first hydraulic control check valve (2.2), and a shuttle valve (2.3). The oil inlet P2 of the multi-way valve (1) is communicated with the oil outlet P1 of the variable pump (3), and the feedback oil port LS of the multi-way valve (1) is communicated with the switching valve group (2). The switching valve group (2) comprises a reversing valve (2.1), a first hydraulic control check valve (2.2), and a shuttle valve (2.3). The P port of the reversing valve (2.1) is communicated with the oil outlet P1 of the variable pump (3), and the B port of the reversing valve (2.1) is communicated with the control cavity of the first hydraulic control check valve (2.2); the oil inlet of the first hydraulic control check valve (2.2) is communicated with the oil outlet P1, and the oil outlet of the first hydraulic control check valve (2.2) is communicated with the first oil inlet of the shuttle valve (2.3); the second oil inlet of the shuttle valve (2.3) is communicated with the feedback oil port LS of the multi-way valve (1), and the oil outlet (2.31) of the shuttle valve is communicated with the variable mechanism (3.1) of the variable pump (3). The B port of the reversing valve (2.1) and the control cavity of the first hydraulic control check valve (2.2) are provided with a check valve (2.5); the allowed flow direction of the check valve (2.5) is from the B port to the control cavity of the first hydraulic control check valve (2.2).

2. The variable pump load sensing and pressure hold switch control system of claim 1, wherein, The switching valve group (2) further comprises an overflow valve (2.4); the oil inlet of the overflow valve (2.4) is communicated with the oil outlet of the first hydraulic control check valve (2.2), and the oil outlet of the overflow valve (2.4) is communicated with the oil tank.

3. The variable pump load sensing and pressure hold switch control system of claim 1, wherein, The oil outlet of the first hydraulic control check valve (2.2) is communicated with the control cavity of the first hydraulic control check valve (2.2).

4. The variable pump load sensing and pressure hold switch control system of claim 3, wherein, The oil outlet of the first hydraulic control check valve (2.2) and the control cavity of the first hydraulic control check valve (2.2) are provided with a first damper (2.6).

5. The variable pump load sensing and pressure hold switch control system of claim 4, wherein, The oil outlet of the first hydraulic control check valve (2.2) and the oil tank are provided with a second damper (2.7); and the oil outlet of the first hydraulic control check valve (2.2) and the first oil inlet of the shuttle valve (2.3) are provided with a third damper (2.8).

6. The variable pump load sensing and pressure hold switch control system of claim 5, wherein, The damping force of the first damper (2.6) and the third damper (2.8) is smaller than the damping force of the second damper (2.7).

7. The variable pump load sensing and pressure hold switch control system of claim 1, wherein, The reversing valve (2.1) is a three-position four-way reversing valve with self-resetting function.

8. The variable pump load sensing and pressure maintaining switchover control system of any one of claims 1-7, wherein, The switching valve group (2) further comprises a second hydraulic control check valve (2.9); the A port of the reversing valve (2.1) is communicated with the control cavity of the second hydraulic control check valve (2.9); the oil inlet of the second hydraulic control check valve (2.9) is communicated with the control cavity of the first hydraulic control check valve (2.2), and the oil outlet of the second hydraulic control check valve (2.9) is communicated with the oil tank.

9. A load sensing and constant pressure switching control method of a variable displacement pump, characterized by, The variable pump load-sensitive and constant-pressure switching control system of claim 8 is used, and specifically as follows: Initial state: the reversing valve (2.1) is in the middle position, the oil liquid from the oil outlet P1 enters the multi-way valve (1), the control oil liquid of the P port of the reversing valve (2.1) is taken from the oil outlet P1, at this time, the first hydraulic control check valve (2.2) is in the closed state, the pressure oil of the oil outlet P1 cannot be fed back to the variable mechanism (3.1); and the oil liquid of the feedback oil port LS of the multi-way valve (1) can be fed back to the variable mechanism (3.1) through the oil outlet (2.31) of the shuttle valve, at this time, the variable pump (3) is in the load-sensitive mode; When the reversing valve (2.1) switches to the upper position, the oil in the outlet P1 enters the control chamber of the first hydraulic control check valve (2.2) to make the first hydraulic control check valve (2.2) conductive, the oil in the outlet P1 reaches the shuttle valve (2.3) through the outlet of the first hydraulic control check valve (2.2), and is fed back to the variable mechanism (3.1) from the outlet (2.31) of the shuttle valve, at this time the variable pump (3) is in constant pressure mode; When the reversing valve (2.1) switches to the lower position, the oil in the outlet P1 enters the control chamber of the second hydraulic control check valve (2.9) through the A port of the reversing valve (2.1) to make the second hydraulic control check valve (2.9) conductive, the oil in the control chamber of the first hydraulic control check valve (2.2) is discharged through the second hydraulic control check valve (2.9), the first hydraulic control check valve (2.2) is closed, at this time the variable pump (3) switches from constant pressure mode to load sensing mode.

Images