Pump controlled hydraulic system standby pressure control system, crane and pressure control method

Abstract

The application discloses a kind of standby pressure control systems of pump control hydraulic system, crane and pressure control method, including electric proportional pump, reversing valve, three-way flow valve, pressure detection unit, control unit and control unit;Through hydraulic and control double regulation, only pump outlet pressure detection is needed, i.e. when crane is in standby state, hydraulic system can be automatically maintained in a standby state, keep system in set pressure state, when handle is operated, system can quickly build pressure, improve system operation responsiveness, at the same time, standby pressure is reasonably controlled, and pump control crane standby pressure is controlled in reasonable range using less sensor, standby pressure of system cannot be changed due to load port pressure change, and the problems of start-up impact and energy waste can be avoided.

Description

Technical Field

[0001] This invention relates to the field of pump-controlled hydraulic systems for cranes, and in particular to a standby pressure control system for a pump-controlled hydraulic system, a crane, and a pressure control method. Background Technology

[0002] Pump-controlled hydraulic systems control the pump's displacement or speed to ensure the flow rate meets system requirements. Pump-controlled cranes utilize pump-controlled hydraulic systems to achieve speed control of operational actions by establishing a control relationship between the size of the control handle opening and the displacement of the electro-proportional pump during operation. Compared to load-sensitive systems, this not only significantly reduces throttling and overflow losses but also features a simpler circuit design, higher reliability, and precise and stable speed control.

[0003] In standby mode, the system has no flow requirement. Normally, the electro-proportional pump is not operating, resulting in no flow output. At this time, the system standby pressure is very low, and energy consumption is low. However, for crane hydraulic systems with long pipelines and large cavities, the lack of flow means that before restarting, the pipeline must first be filled with oil to establish system pressure, before the load can be driven, causing a delay in system response. Therefore, it is necessary to maintain a suitable pressure state in the pump-controlled hydraulic system during standby to improve system response. At the same time, the standby pressure must not be too high, otherwise it may lead to starting shock and energy waste.

[0004] Chinese patent CN105604996A discloses a control method and system for achieving adaptive matching between system pressure and load pressure in a load-sensitive control system, control method, and hydraulic system. This load-sensitive control system includes a variable displacement pump, a load feedback oil circuit, and a differential pressure control valve. The differential pressure control valve is connected to the variable displacement pump and the load feedback oil circuit, allowing the difference between the outlet pressure of the variable displacement pump and the load pressure in the load feedback oil circuit to vary. This patent provides a load-sensitive system with variable differential pressure, improving the speed regulation characteristics of the load-sensitive system. However, the system design is primarily for load-sensitive pump systems and is not applicable to pump-controlled hydraulic systems.

[0005] Chinese patent CN104314927A discloses a load-sensitive hydraulic control system and method, and a control method and system for engineering machinery. The load-sensitive hydraulic control system includes an electric pump, a load-sensitive valve, a first pressure sensor, a second pressure sensor, and a controller. The inlet of the load-sensitive valve is connected to the outlet of the electric pump. The first pressure sensor measures a first pressure value at the outlet of the electric pump, and the second pressure sensor measures a second pressure value at the load feedback port of the load-sensitive valve. The controller adjusts the control current of the electric pump based on the difference between the first and second pressure values, making the difference equal to a preset value. This solution adjusts the input current of the electric pump by adjusting the difference between the outlet pressure of the electric pump and the feedback port pressure of the load-sensitive valve, overcoming the limitation that load-sensitive hydraulic systems can only be used with a load-sensitive pump and a load-sensitive valve. However, the pump control current requires at least two pressure sensors—one at the pump outlet and one at the load feedback port—resulting in high design costs. Furthermore, in standby mode, if the load feedback pressure remains high, the pump outlet pressure will also be adjusted very high, leading to energy waste and potentially causing a shock during the next start-up operation.

[0006] Chinese patent CN111677724A discloses a phased composite control method for a hydraulic system, including a control method, controller, and storage medium for hydraulic systems in engineering machinery. The method involves dividing the electric control handle into a preparation zone and an operating zone based on its operating amplitude. When the electric control handle is in the preparation zone, the hydraulic pump is in a standby zone. As the operating amplitude of the electric control handle changes from the initial value to the final value of the preparation zone, the hydraulic pump maintains a preset minimum displacement. As the operating amplitude of the electric control handle changes from the initial value to the final value of the operating zone, the hydraulic pump's displacement increases from the preset minimum displacement to the maximum displacement. This control method adds a preparation zone between the standby and operating states as a transition. However, in actual normal use, the handle cannot remain in the preparation zone for a sufficient time during all operations. The adjustment time in the standby state is short, making it difficult to adjust properly, or even impossible to adjust in time before entering the normal operating zone. Summary of the Invention

[0007] Purpose of the invention: In order to solve the problems existing in the prior art, the present invention provides a standby pressure control system for a pump-controlled hydraulic system, a crane and a pressure control method, which effectively improves the responsiveness of the system and avoids the problems of start-up shock and energy waste.

[0008] Technical Solution: To achieve the above objective, the present invention adopts the following technical solution: A standby pressure control system for a pump-controlled hydraulic system, comprising: an electric proportional pump, a reversing valve, a three-way flow valve, a pressure detection unit, a control unit, and an operation control unit; the three-way flow valve is connected to the electric proportional pump, the reversing valve and a hydraulic oil tank respectively; the pressure detection unit is connected to the electric proportional pump and detects the pump outlet pressure; the control unit is connected to the pressure detection unit and the operation control unit, controls the current of the electric proportional pump according to the received pressure signal and standby state signal, so that the system standby pressure meets the set requirement, and sends out prompt information when the adjustment is abnormal; the operation control unit detects whether the system is in standby.

[0009] The pressure detection unit is a pressure sensor or a pressure switch.

[0010] Further, the electric proportional pump has a proportional displacement adjustment function.

[0011] Further, an oil inlet of the reversing valve is connected to an oil outlet of the electric proportional pump, and an oil outlet of the reversing valve is connected to a load.

[0012] Further, an oil inlet of the three-way flow valve is connected to the oil outlet of the electric proportional pump, an oil outlet of the three-way flow valve is connected to the hydraulic oil tank, and a spring cavity of the three-way flow valve is connected to a load port of the reversing valve.

[0013] Further, the system further comprises a display unit that receives the adjustment abnormality information sent by the display control unit.

[0014] Further, the pressure detection unit is connected to the oil outlet of the electric proportional pump and detects the pump outlet pressure.

[0015] The present invention also discloses a crane comprising the above standby pressure control system for a pump-controlled hydraulic system.

[0016] A control method for a standby pressure control system of a pump-controlled hydraulic system, comprising the following steps:

[0017] (1) The operation control unit judges in real time whether the flow demand of the hydraulic system requires entering a standby state, and transmits the standby state signal to the control unit;

[0018] (2) The control unit sets a standby pressure hysteresis interval P1~P2, where P1<P2;

[0019] (3) An initial pre-tightening pressure value of the three-way flow valve is set as P1, when the standby pressure is too high, flow is split and pressure is reduced by opening the three-way flow valve;

[0020] (4) The pressure detection unit monitors the pressure P at the pump oil outlet in real time, when P<P1, the control unit increases the current I of the electric proportional pump until the set state is reached;

[0021] (5) When P>P2, the control unit reduces the electric proportional pump current I, performs flow splitting and pressure reduction through the three-way flow valve until the set state is reached;

[0022] (6) When P1<P<P2, the control unit does not adjust the pump current I;

[0023] (7) An adjustment amplitude limiting range Imin~Imax for the pump control current is set. When the current exceeds the adjustment range, no further adjustment is performed even if the pressure is not adjusted in place;

[0024] (8) When the pump current adjustment reaches the amplitude limiting boundary and the pressure is still not adjusted in place, the control unit sends relevant prompt information to the display unit.

[0025] Further, in steps (4) and (5), in order to avoid pressure fluctuation at the P1 / P2 critical point and reduce the number of adjustments, the adjustment is stopped after the pump current I is adjusted until P>(P1+P2) / 2.

[0026] Further, in step (7), when the system pressure P<P1 and the pump current I≥Imax, the pump current is maintained at Imax and will not be increased further; when the system pressure P>P2 and the pump current I≤Imin, the pump current is maintained at Imin and will not be reduced further.

[0027] Beneficial effects: The present invention has the following advantages: through dual hydraulic and control adjustment, only one pressure detection at the pump oil outlet is required, so that when the crane is in a standby state, the hydraulic system can automatically maintain a standby state and keep the system at a set pressure. When a handle operation is performed, the system can build pressure quickly, which improves the operational responsiveness of the system. Meanwhile, the standby pressure is reasonably controlled, the standby pressure of the pump-controlled crane is controlled within a reasonable range with fewer sensors, the system standby pressure will not change with the change of load port pressure, and the problems of start-up impact and energy waste can be avoided. Description of Drawings

[0028] Figure 1 is a schematic structural diagram of the system in Embodiment 1 of the present invention;

[0029] Figure 2 is a schematic diagram of the flow-pressure characteristic curve of the three-way flow valve in Embodiment 1 of the present invention. Detailed Description of Embodiments

[0030] Embodiment 1:

[0031] The invention discloses a crane, as Figure 1 shown, the standby pressure control system of the pump-controlled hydraulic system thereof comprises: an electric proportional pump 1, a reversing valve 2, a three-way flow valve 3, a pressure detection unit 4, a control unit 5, a control unit 6, a display unit 7, a load 8 and a hydraulic oil tank 9;

[0032] The electric proportional pump 1 has a proportional displacement adjustment function. The oil inlet of the reversing valve 2 is connected to the oil outlet of the electric proportional pump 1, and the oil outlet is connected to the load 8.

[0033] The inlet of the three-way flow valve 3 is connected to the outlet of the electro-proportional pump 1, and the outlet is connected to the hydraulic oil tank 9. The spring chamber is connected to the load port of the directional valve 2. When the pressure difference between the inlet of the three-way flow valve 3 and the spring chamber exceeds the set preload pressure of the spring chamber, the three-way flow valve 3 opens, and the oil is diverted to reduce the pressure at the inlet.

[0034] The pressure detection unit 4 is a pressure sensor connected to the oil outlet of the proportional pump 1 to detect the pump outlet pressure.

[0035] The control unit 5 is connected to the pressure detection unit 4 and the control unit 6. It controls the current of the electric proportional pump 1 according to the received pressure signal and standby status signal so that the system standby pressure meets the set requirements. When the adjustment is abnormal, it sends a prompt message to the display unit 7. The control unit 6 detects whether the system is in standby mode.

[0036] The control method for the standby pressure control system of the above-mentioned pump-controlled hydraulic system includes the following steps:

[0037] (1) The control unit 6 judges the flow demand of the hydraulic system in real time. When the system flow demand is 0, it judges that the system enters the standby state and transmits the standby state signal to the control unit 5.

[0038] (2) Control unit 5 sets the standby pressure value, taking into account system fluctuations and adjustment deviations, and sets the standby pressure hysteresis range P1 to P2, where P1 <P2;

[0039] (3) Set the initial preload pressure of the spring chamber of the three-way flow valve 3 to P1. In the standby state, the reversing valve 2 does not work and the load port pressure is almost 0. At this time, the pressure difference of the three-way flow valve 3 is approximately equal to the pump outlet pressure. When the pump outlet pressure exceeds the preload pressure P1 of the three-way flow valve 3, the three-way flow valve 3 will open to divert the flow.

[0040] Due to limitations in the oil passage design of the three-way flow valve 3, when the pump outlet flow rate changes, the control pressure of the three-way flow valve 3 cannot remain constant at the P value; instead, it increases with the increase of flow rate, as shown in the characteristic curve. Figure 2 As shown.

[0041] To ensure that the standby pressure of the control system is not higher than P2, the pump flow rate must be controlled to not exceed Q2; at the same time, the system pressure must also be not lower than P1, which requires controlling the pump flow rate to be not lower than Q1.

[0042] However, the electric proportional pump is affected by factors such as rotation speed, internal leakage of the system, and its own processing reliability. A single control method can hardly stably control the flow rate within Q1 to Q2, and further makes it difficult to maintain the system standby pressure within P1 to P2.

[0043] Therefore, the pump current control method of the present application is designed. On the basis that the three-way flow valve 3 controls the standby pressure, stable control of the system standby pressure is realized through adjustment of the pump current.

[0044] (4) The pressure detection unit 4 monitors the pressure P at the oil outlet of the pump in real time. When P<P1, the control unit 5 increases the current I of the electric proportional pump 1 until the pressure at the oil outlet of the pump is greater than P1. In order to avoid pressure fluctuation at the critical point of P1 and reduce the number of adjustments, the adjustment is stopped after adjusting the pump current I to make P>(P1+P2) / 2.

[0045] (5) When P>P2, the control unit 5 reduces the current I of the electric proportional pump 1, and performs shunting and pressure reduction through the three-way flow valve 3 until the pressure at the oil outlet of the pump is less than P2. In order to avoid pressure fluctuation at the critical point of P2 and reduce the number of adjustments, the adjustment is stopped after adjusting the pump current I to make P<(P1+P2) / 2.

[0046] (6) When P1<P<P2, the system pressure is within the set hysteresis interval, and the control unit 5 does not adjust the pump current I.

[0047] (7) In order to avoid out-of-control regulation caused by abnormalities of system components or matching, the control unit 5 is further provided with a regulation amplitude limiting link for the pump current in the standby state, and the regulation range of the pump control current is Imin~Imax. When the system pressure P<P1 and the pump current I≥Imax, the pump current maintains Imax and does not increase further; when the system pressure P>P2 and the pump current I≤Imin, the pump current maintains Imin and does not decrease further.

[0048] (8) When the pump current regulation reaches the amplitude limiting boundary and the adjustment is still not completed, the control unit 5 sends relevant prompt information to the display unit 7 to prompt the user to check the relevant content of the system.

[0049] Through dual regulation of hydraulic pressure and control, the present invention only requires one pressure detection at the pump oil outlet, so that when the crane is in the standby state, the hydraulic system can automatically maintain a standby state and keep the system in a set pressure state. When a handle operation is performed, the system can build pressure quickly, which improves the operational responsiveness of the system. Meanwhile, the present invention reasonably controls the standby pressure, controls the standby pressure of the pump-controlled crane within a reasonable range with few sensors, avoids the change of system standby pressure caused by the change of load port pressure, and can avoid the problems of start-up impact and energy waste.

Claims

1. A control method for a standby pressure control system of a pump-controlled hydraulic system, characterized in that, The following standby pressure control system for a pump-controlled hydraulic system is adopted: an electric proportional pump, a reversing valve, a three-way flow valve, a pressure detection unit, a control unit and a control unit; the three-way flow valve is connected to the electric proportional pump, the reversing valve and a hydraulic oil tank respectively; the pressure detection unit is connected to the electric proportional pump to detect the pump outlet pressure; the control unit is connected to the pressure detection unit and the control unit, controls the current of the electric proportional pump according to the received pressure signal and standby state signal, so that the system standby pressure meets the set requirements, and sends out prompt information when adjustment abnormality occurs; the control unit detects whether the system is in standby; The specific control method comprises the following steps: (1) The control unit judges the flow demand of the hydraulic system in real time to determine whether to enter a standby state, and transmits a standby state signal to the control unit; (2) The control unit sets a standby pressure hysteresis interval P1~P2, wherein P1<P2; (3) The initial pre-tightening pressure of the three-way flow valve is set as P1, and when the standby pressure is too high, the three-way flow valve is opened for flow splitting and pressure reduction; (4) The pressure detection unit monitors the pressure P at the oil outlet of the pump in real time. When P<P1, the control unit increases the current I of the electric proportional pump until the set state is reached; (5) When P>P2, the control unit reduces the current I of the electric proportional pump, and performs flow splitting and pressure reduction through the three-way flow valve until the set state is reached; (6) When P1<P<P2, the control unit does not adjust the pump current I; (7) An adjustment limiting range Imin~Imax for the pump control current is set, and when the current exceeds the adjustment range, no further adjustment is performed even if the pressure has not been adjusted in place; (8) When the pump current adjustment reaches the amplitude limiting boundary and is still not adjusted in place, the control unit sends relevant prompt information to the display unit.

2. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that: The electric proportional pump has a proportional displacement adjustment function.

3. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that: An oil inlet of the reversing valve is connected to an oil outlet of the electric proportional pump, and an oil outlet of the reversing valve is connected to a load.

4. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that: An oil inlet of the three-way flow valve is connected to the oil outlet of the electric proportional pump, an oil outlet of the three-way flow valve is connected to the hydraulic oil tank, and a spring cavity of the three-way flow valve is connected to a load port of the reversing valve.

5. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that... The system further comprises a display unit for receiving the adjustment abnormality information sent by the control unit.

6. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that: The pressure detection unit is connected to the oil outlet of the electric proportional pump to detect the pump outlet pressure.

7. A crane comprising the control method of the standby pressure control system for a pump-controlled hydraulic system according to any one of claims 1 to 6.

8. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that: In steps (4) and (5), in order to avoid pressure fluctuation at the critical point of P1 / P2 and reduce the number of adjustments, the adjustment is stopped after the pump current I is adjusted to make P>(P1+P2) / 2.

9. The control method for the standby pressure control system of the pump-controlled hydraulic system according to claim 1, characterized in that: In step (7), when the system pressure P<P1 and the pump current I≥Imax, the pump current maintains Imax and is not increased any further; when the system pressure P>P2 and the pump current I≤Imin, the pump current maintains Imin and is not decreased any further.

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