Hydrostatic synchronous control system for straddle carrier and straddle carrier

Abstract

The invention relates to a hydrostatic synchronous control system for a straddle carrier and the straddle carrier. The control system comprises a variable pump, the first oil port is connected with a first oil way, and the second oil port is connected with a second oil way. An oil inlet of the first diverter valve is connected to the first oil way, and a first working oil port and a second working oil port are both connected with motors; the first working oil port and the second working oil port of the first diverter valve are both provided with the pressure release valves, and the pressure release valves are configured to release overpressure oil liquid to a pressure release oil way when the pressure of the connected oil ports exceeds a preset threshold value; two oil inlets of the shuttle valve are connected with the first oil way and the second oil way respectively, and an oil outlet of the shuttle valve is connected with the hydraulic control end of the first diverter valve; the pressure of the first working oil port of the first flow divider valve and the pressure of the second working oil port are kept consistent through the pressure release valve, so that the flow of hydraulic oil output by the first working oil port of the first flow divider valve and the flow of hydraulic oil output by the second working oil port are synchronous, and the purpose of equally dividing the flow is achieved.

Description

Technical Field

[0001] The present invention relates to a hydrostatic synchronous control system for a straddle carrier and a straddle carrier. Background Art

[0002] With the growth of global trade, the demand for container transportation has surged. As a core equipment in ports and yards, the operation efficiency of straddle carriers directly affects logistics costs. Due to insufficient coordination of multiple axles, traditional straddle carriers have high energy consumption and low efficiency. There is an urgent need to optimize power distribution through energy-saving control, reduce no-load and waiting times, and improve overall transportation efficiency. When multiple axle vehicles are combined for application, the problem of synchronous control of multiple axle vehicles needs to be solved. When the load center of gravity is asymmetric, if the rotational speeds of each hydraulic motor are different, it will affect the operation safety and reliability of the vehicle.

[0003] The main methods adopted in the synchronous control of hydraulic motors for multi-axle vehicles or straddle carriers driven by hydraulic motors are the synchronous flow dividing motor method and the proportional control valve method. Among them, the synchronous flow dividing motor method utilizes the flow distribution function of the hydraulic synchronous flow dividing motor to distribute hydraulic oil to each actuator in proportion. Its internal structure can automatically adjust flow differences. Although this method can achieve precise control of the speeds of each actuator, it is difficult to synchronize the flow rates flowing into multiple hydraulic motors. Correspondingly, it is difficult to keep the actuator speeds allocated to different hydraulic motors consistent. The proportional control valve method uses a proportional control valve to control the oil flow rate flowing to each hydraulic motor. Position and speed feedback are obtained through a feedback device (such as an encoder) installed on the motor shaft. The controller reads the feedback and sends a signal to the proportional control valve to implement closed-loop control to continuously adjust to maintain synchronization. This method mainly performs feedback control on the proportional control valve through the motor speed, and adjusts the valve core opening of the proportional control valve in real time to make the flow rates flowing into each hydraulic motor consistent. The control method of this method is cumbersome, and due to the fluctuation of the motor speed, there are control errors between each proportional control valve, and it is difficult to stably achieve speed synchronization between each hydraulic motor during actual use. Summary of the Invention

[0004] The purpose of the present invention is to provide a hydrostatic synchronous control system for a straddle carrier and a straddle carrier. By connecting a first oil circuit output by a variable pump through a first flow dividing valve, and then making the oil port pressures of the first working oil port and the second working oil port of the first flow dividing valve consistent through a pressure relief valve, the hydraulic oil flow rates output from the first working oil port and the second working oil port of the first flow dividing valve are synchronized, so as to achieve the purpose of evenly distributing the flow rate to each hydraulic motor.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a hydrostatic synchronous control system for a straddle carrier, which includes: A variable pump, with a first oil port connected to a first oil circuit and a second oil port connected to a second oil circuit; The first flow control valve, the oil inlet is connected to the first oil path, and both the first working oil port and the second working oil port are connected to motors. The pressure relief valve, pressure relief valves are provided at both the first working oil port and the second working oil port of the first flow control valve, and the pressure relief valve is configured to drain the overpressure hydraulic fluid to the pressure relief oil path when the pressure of the connected oil port exceeds a preset threshold. The shuttle valve, two oil inlets are respectively connected to the first oil path and the second oil path, and the oil outlet of the shuttle valve is connected to the hydraulic control end of the first flow control valve. When the control oil output from the oil outlet of the shuttle valve acts on the hydraulic control end of the first flow control valve, the first flow control valve switches to the first working position; the oil inlet of the first flow control valve communicates with the first working oil port through the first throttle hole and communicates with the second working oil port through the second throttle hole.

[0006] Optionally, it further includes: The second flow control valve, the oil inlet is connected to the first working oil port of the first flow control valve, the first working oil port is connected to the first end of the first motor, and the second working oil port is connected to the first end of the second motor. The third flow control valve, the oil inlet is connected to the second working oil port of the first flow control valve, the first working oil port is connected to the first end of the third motor, and the second working oil port is connected to the first end of the fourth motor. The second ends of the first motor, the second motor, the third motor and the fourth motor are all connected to the second oil path upstream of the shuttle valve.

[0007] Optionally, pressure relief valves are connected to both the first working oil port and the second working oil port of the second flow control valve, and both the first working oil port and the second working oil port of the third flow control valve.

[0008] Optionally, the oil inlet of the pressure relief valve is connected to the working oil port of the corresponding flow control valve, and the oil outlet of the pressure relief valve is connected to the pressure relief oil path; when the pressure of the oil port connected to the oil inlet of the pressure relief valve does not exceed the preset threshold, the oil inlet and the oil outlet of the pressure relief valve are cut off, and when the pressure of the oil port connected to the oil inlet of the pressure relief valve exceeds the preset threshold, the oil inlet and the oil outlet of the pressure relief valve are communicated.

[0009] Optionally, the oil outlet of the shuttle valve is connected in parallel to the hydraulic control ends of the first flow control valve, the second flow control valve and the third flow control valve after passing through the reversing valve; The reversing valve has a first working position and a second working position. When the reversing valve is in the first working position, the hydraulic control ends of the first flow control valve, the second flow control valve and the third flow control valve are communicated with the fuel tank; when the reversing valve is in the second working position, the hydraulic control ends of the first flow control valve, the second flow control valve and the third flow control valve are communicated with the oil outlet of the shuttle valve.

[0010] Optionally, it further includes: A piston cylinder, which is connected to the variable pump to control the displacement of the variable pump; Both ends of the piston cylinder are respectively connected to the first oil port of the first electro-hydraulic proportional valve and the first oil port of the second electro-hydraulic proportional valve; the second oil ports of the first electro-hydraulic proportional valve and the second electro-hydraulic proportional valve are connected in parallel and then connected to the pressure relief oil circuit; the third oil ports of the first electro-hydraulic proportional valve and the second electro-hydraulic proportional valve are connected in parallel and then connected to an external port through a third oil circuit; by adjusting the spool position and spool opening of the first electro-hydraulic proportional valve and the second electro-hydraulic proportional valve, the position of the piston cylinder can be adjusted to control the displacement of the variable pump.

[0011] Optionally, it further includes: A pressure cut-off valve, whose inlet is connected to the third oil circuit; An energy-saving shuttle valve, whose two inlets are respectively connected to the first oil circuit and the second oil circuit, and the outlet is connected to the control end of the pressure cut-off valve; When the pressure oil output from the outlet of the energy-saving shuttle valve exceeds a preset threshold and acts on the control end of the pressure cut-off valve, the inlet of the pressure cut-off valve is connected to the fuel tank, the piston cylinder maintains its position, and the variable pump outputs flow at a preset minimum displacement.

[0012] Optionally, it further includes: A make-up oil pump, which is coaxially connected to the variable pump, and the hydraulic oil output by the make-up oil pump can be unidirectionally transported to the first oil circuit and the second oil circuit.

[0013] In a second aspect, the present invention provides a straddle carrier, which includes the static hydraulic synchronous control system for the straddle carrier described above.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention equalizes the flow through the first flow dividing valve and the pressure relief valve. When the oil port pressure at the first working oil port or the second working oil port of the first flow dividing valve exceeds the preset pressure threshold of the pressure relief valve, the pressure relief valve can discharge the excess hydraulic oil to the pressure relief oil circuit, so that the pressures at the first working oil port and the second working oil port of the first flow dividing valve are kept consistent. The hydraulic oil flowing into the inlet of the first flow dividing valve can be evenly divided and flow out through the first working oil port and the second working oil port, so that the flow rates flowing into each hydraulic motor can be kept consistent. Then, by changing the displacement of the electro-hydraulic proportional (EP) motor through an electric signal, the consistency of the rotational speed of each hydraulic motor can be ensured. There is no need to perform real-time monitoring on the motor speed for feedback control. The control method is simple and stable and can maintain a high control accuracy. Description of the Drawings

[0015] Figure 1 It is a schematic structural diagram of the static hydraulic synchronous control system for the straddle carrier in Embodiment 1; Figure 2 For Figure 1Structural schematic diagram from another perspective; Figure 3 It is the hydraulic system structure diagram of the hydrostatic synchronous control system for the straddle carrier in Embodiment 1.

[0016] Reference numerals in the figure: closed pump system 1; make-up oil pump 2; electro-hydraulic proportional flow equalization system 3; drive wheel 4; hydraulic motor 5; first motor 51; second motor 52; third motor 53; fourth motor 54; second flow dividing valve 6; third flow dividing valve 7; first flow dividing valve 8; reversing valve 19; shuttle valve 9; pressure relief valve 10; overflow valve 11; first high-pressure overflow valve 101; second high-pressure overflow valve 102; pressure cut-off valve 12; energy-saving shuttle valve 13; variable pump 14; piston cylinder 15; high-pressure filter 16. Detailed implementation manners

[0017] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more. In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "mounted", "connected", "coupled" should be understood in a broad sense, for example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection, an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood through specific situations.

[0018] The present invention will be further described below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and cannot be used to limit the protection scope of the present invention. Embodiment 1

[0019] In order to make the purpose, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0020] The present invention relates to a hydrostatic synchronous control system for a straddle carrier, which includes a closed-loop pump system 1 and an electro-hydraulic proportional flow equalization system 3. As Figure 1 and Figure 2 shown in the figure, it is a schematic diagram of the variable displacement bidirectional closed-loop pump system 1 connected to one of the hydraulic motors 5 through a hydraulic pipeline. The drive wheel 4 is connected to the hydraulic motor 5 through a speed reducer. Figure 3 This is a schematic diagram of the hydraulic system in which the closed-loop pump outputs hydraulic oil to drive the hydraulic motor 5. The bidirectional closed-loop pump system 1 is mainly used to provide hydraulic oil for each hydraulic motor 5, and the electro-hydraulic proportional flow equalization system 3 is used to evenly distribute the hydraulic oil provided by the closed-loop pump system 1 to each hydraulic motor 5. The bidirectional closed-loop pump system 1 includes a variable pump 14. A first oil circuit is connected to the first oil port of the variable pump 14, and a second oil circuit is connected to the second oil port. The variable pump 14 is coaxially connected with a makeup oil pump 2, and the hydraulic oil output by the makeup oil pump 2 can be unidirectionally conveyed to the first oil circuit and the second oil circuit. The hydraulic oil output by the makeup oil pump 2 is connected to the first oil circuit and the second oil circuit in parallel through a filter 16. A first high-pressure overflow valve 101 is provided between the filter 16 and the first oil circuit, and a second high-pressure overflow valve 102 is provided between the filter 16 and the second oil circuit. The first high-pressure overflow valve 101 and the second high-pressure overflow valve 102 are used to open when the pressure output by the makeup oil pump 2 exceeds a preset threshold to ensure the safety of the two oil circuits.

[0021] The electro-hydraulic proportional flow equalization system 3 includes a first flow dividing valve 8 and a shuttle valve 9. The inlet port of the first flow dividing valve 8 is connected to the first oil circuit, and both the first working oil port and the second working oil port are connected to motors. Pressure relief valves 10 are provided at both the first working oil port and the second working oil port of the first flow dividing valve 8. The pressure relief valve 10 is configured to drain the overpressure hydraulic oil to the pressure relief oil circuit when the pressure at the connected oil port exceeds a preset threshold. Specifically, the inlet port of the pressure relief valve 10 is connected to the working oil port of the corresponding flow dividing valve, and the outlet port of the pressure relief valve 10 is connected to the pressure relief oil circuit. The left end of the pressure relief valve 10 is connected to its inlet port, and a return spring is provided at the right end of the pressure relief valve 10. When the pressure at the oil port connected to the inlet port of the pressure relief valve 10 does not exceed the preset threshold, under the action of the return spring, the spool position of the pressure relief valve 10 is in the cut-off position, and the inlet port and the outlet port of the pressure relief valve 10 are cut off. When the pressure at the oil port connected to the inlet port of the pressure relief valve 10 (the first working oil port or the second working oil port of the first flow dividing valve) exceeds the preset threshold, the oil pressure at the inlet port of the pressure relief valve 10 acts on the left end of the pressure relief valve 10 to push the spool position to move, and the pressure relief valve 10 is in the flow-through position, and the inlet port and the outlet port of the pressure relief valve 10 are connected.

[0022] The two oil inlets of the shuttle valve 9 are respectively connected to the first oil circuit and the second oil circuit, and the oil outlet of the shuttle valve 9 is connected to the hydraulic control end of the first flow dividing valve 8; when the control oil output from the oil outlet of the shuttle valve 9 acts on the hydraulic control end of the first flow dividing valve 8, the first flow dividing valve 8 switches to the first working position; the oil inlet of the first flow dividing valve 8 is communicated with the first working oil port through the first throttle hole and with the second working oil port through the second throttle hole. The first throttle hole and the second throttle hole are used to slow down the flow rate of the hydraulic oil and prevent the hydraulic motor from being impacted due to pressure fluctuations.

[0023] Illustrated in combination with the control principle of the control system, the variable pump 14 can work bidirectionally to cooperate with the rotation direction of the electro-hydraulic proportional motor 5 to control the movement of the straddle carrier. Taking the forward direction as an example, at this time, the variable pump 14 rotates forward, and at the same time, the make-up oil pump 13 is started, and the closed-loop pump system 1 starts to work. The oil output by the make-up oil pump 13 is filtered by the filter 4 to ensure the cleanliness of the oil in the closed-loop system. After the high pressures of the first oil circuit and the second oil circuit are compared by the shuttle valve 9, the hydraulic oil on the high-pressure side is led to the first flow dividing valve 7 through the reversing valve 8. The first flow dividing valve 8 has two modes. One is the free mode, that is, the first flow dividing valve 8 is in the second working position. At this time, the hydraulic oil flowing into the oil inlet of the first flow dividing valve 8 is directly output without passing through the throttle hole. The other is the synchronous control mode, that is, the first flow dividing valve 8 is in the first working position. At this time, the hydraulic oil flowing into the oil inlet of the first flow dividing valve 8 is output after passing through the throttle hole, and the overpressure oil is discharged to the pressure relief oil circuit by the pressure relief valve 10 to make the pressures of the first working oil port and the second working oil port of the first flow dividing valve 8 consistent, both being the preset threshold value, so as to equally divide the hydraulic oil volume. For the deviation of the flow rate generated by the flow loss caused by the pipeline effect in the flow rate flowing into the electro-hydraulic proportional (EP) motor 5, in this embodiment, the first flow dividing valve 7 can ensure that the flow rates of the oil output from the first working oil port and the second working oil port are consistent, and the valve opening and the preset threshold value of the pressure relief valve can also be changed by an electric signal to adjust the output flow rate. Thus, under the action of the first flow dividing valve 8, the flow rates obtained by the multiple hydraulic motors 5 in this embodiment are all consistent, which is difficult to achieve by the existing methods. In this embodiment, the displacement of the electro-hydraulic proportional (EP) motor 5 is changed by an electric signal to ensure the consistency of the rotational speeds of each hydraulic motor 5, so as to achieve the energy-saving effect of small displacement, high speed under no-load conditions, large displacement under heavy-load conditions, and small speed.

[0024] Further, taking the control system supplying oil to four motors as an example, the control system in this embodiment further includes a second flow dividing valve 6 and a third flow dividing valve 7. The oil inlet of the second flow dividing valve 6 is connected to the first working oil port of the first flow dividing valve 8. The first working oil port of the second flow dividing valve 6 is connected to the first end of the first motor 51, and the second working oil port is connected to the first end of the second motor 52. The oil inlet of the third flow dividing valve 7 is connected to the second working oil port of the first flow dividing valve 8. The first working oil port is connected to the first end of the third motor 53, and the second working oil port is connected to the first end of the fourth motor 54. The second ends of the first motor 51, the second motor 52, the third motor 53, and the fourth motor 54 are all connected to the second oil circuit upstream of the shuttle valve 9. Pressure relief valves 10 are connected to the first working oil port and the second working oil port of the second flow dividing valve 6, and the first working oil port and the second working oil port of the third flow dividing valve 7. The oil outlet of the shuttle valve 9 is connected in parallel to the hydraulic control ends of the first flow dividing valve 8, the second flow dividing valve 6, and the third flow dividing valve 7 after passing through the reversing valve 19. The first motor 51, the second motor 52, the third motor 53, and the fourth motor 54 are all electro-hydraulic proportional (EP) motors 5. The reversing valve 19 has a first working position and a second working position. When the reversing valve 19 is in the first working position, the hydraulic control ends of the first flow dividing valve 8, the second flow dividing valve 6, and the third flow dividing valve 7 are communicated with the fuel tank. At this time, the hydraulic control ends of the first flow dividing valve 8, the second flow dividing valve 6, and the third flow dividing valve 7 are not affected by the control oil and are in the second working position. When the reversing valve 19 is in the second working position, the hydraulic control ends of the first flow dividing valve 8, the second flow dividing valve 6, and the third flow dividing valve 7 are communicated with the oil outlet of the shuttle valve 9. At this time, the hydraulic control ends of the first flow dividing valve 8, the second flow dividing valve 6, and the third flow dividing valve 7 are affected by the control oil and are in the first working position. The hydraulic oil throttled by the throttle orifice is then relieved of pressure by the pressure relief oil to achieve flow equalization.

[0025] The above oil circuit flow direction is the oil circuit flow direction when the straddle carrier moves forward. When the straddle carrier moves backward, the hydraulic oil output by the variable pump 14 reaches the second ends of the first motor 51, the second motor 52, the third motor 53 and the fourth motor 54 through the second oil circuit. The first flow control valve 8, the second flow control valve 6 and the third flow control valve 7 are switched to the first working position under the action of the hydraulic oil output by the shuttle valve 19 (the throttle orifice throttles the flowing hydraulic oil). The first ends of the first motor 51 and the second motor 52 enter through the first working oil port and the second working oil port of the second flow control valve 6 respectively, and merge and flow out from the oil inlet of the second flow control valve 6. The first ends of the third motor 53 and the fourth motor 54 enter through the first working oil port and the second working oil port of the third flow control valve 7 respectively, and merge and flow out from the oil inlet of the third flow control valve 7. The hydraulic oil flowing out from the oil inlets of the second flow control valve 6 and the third flow control valve 7 merges through the first flow control valve 8 into the first oil circuit and flows back to the variable pump 14 through the first oil circuit. The hydraulic oil flow when the straddle carrier moves backward is the reverse process of when the straddle carrier moves forward. The flow rates of the respective hydraulic motors when the straddle carrier moves backward remain consistent so as to keep the motor speeds synchronized.

[0026] Further, the closed-loop pump system 1 in this embodiment also has an energy-saving function. The closed-loop pump system 1 in this embodiment further includes a piston cylinder 15, and the piston cylinder 15 is connected to the variable pump 14 to control the displacement of the variable pump 14. The two ends of the piston cylinder 15 are respectively connected to the first oil port of the first electro-hydraulic proportional valve 17 and the first oil port of the second electro-hydraulic proportional valve 18; the second oil ports of the first electro-hydraulic proportional valve 17 and the second electro-hydraulic proportional valve 18 are connected in parallel and then connected to the pressure relief oil circuit; if the oil port pressure of the second oil port of the first electro-hydraulic proportional valve 17 or the second oil port of the second electro-hydraulic proportional valve 18 exceeds the preset threshold, the relief valve 11 on the pressure relief oil circuit opens, and the second oil ports of the first electro-hydraulic proportional valve 17 and the second electro-hydraulic proportional valve 18 are directly connected to the fuel tank in parallel to protect the system safety. The third oil ports of the first electro-hydraulic proportional valve 17 and the second electro-hydraulic proportional valve 18 are connected in parallel and then connected to an external port through a third oil circuit (connected to a balanced load to keep the position of the piston cylinder 15 stable); by adjusting the spool positions and spool openings of the first electro-hydraulic proportional valve 17 and the second electro-hydraulic proportional valve 18, the flow rate can be changed so that the piston cylinder 15 moves left and right to control the displacement of the variable pump 14.

[0027] In addition, to achieve the energy-saving function, the closed-loop pump system 1 in this embodiment further includes a pressure cut-off valve 12 and an energy-saving shuttle valve 13. The inlet of the pressure cut-off valve 12 is connected to the third oil circuit; the two inlets of the energy-saving shuttle valve 13 are respectively connected to the first oil circuit and the second oil circuit, and the outlet is connected to the control end of the pressure cut-off valve 12; when the pressures of the first oil circuit and the second oil circuit are compared by the energy-saving shuttle valve 13, the outlet of the energy-saving shuttle valve 13 outputs. If the pressure at the outlet of the energy-saving shuttle valve 13 exceeds the preset threshold of the pressure cut-off valve 12 (determined by a pre-arranged spring), the inlet of the pressure switching valve is connected to the fuel tank, the oil pressures at the third ports of the first electro-hydraulic proportional valve 17 and the second electro-hydraulic proportional valve 18 disappear, the control pressure returns to the housing, the control oil is depressurized, the swash plate of the piston cylinder 15 automatically returns to the middle position, the piston cylinder 15 remains in the middle position, and the variable pump 14 outputs flow at a preset minimum displacement. This flow maintains the internal leakage of the system, keeps the pressure, and achieves the energy-saving effect. The first electro-hydraulic proportional valve 17, the second electro-hydraulic proportional valve 18, the pressure cut-off valve 12, the first high-pressure relief valve 101, the second high-pressure relief valve 102 and the filter 16 in this embodiment are all directly embedded on the main variable pump 14, reducing pipeline connections and improving the sealing performance and integration degree. Embodiment 2

[0028] Based on the same inventive concept as in Embodiment 1, this embodiment provides a straddle carrier, which includes the hydrostatic synchronous control system for straddle carriers described above.

[0029] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A hydrostatic synchronous control system for a straddle carrier, characterized in that: Comprising: A variable pump (14) with a first oil port connected to a first oil circuit and a second oil port connected to a second oil circuit; A first flow dividing valve (8) with an inlet connected to the first oil circuit, and a first working oil port and a second working oil port of the first flow dividing valve (8) are respectively connected to corresponding hydraulic motors (5); A pressure relief valve (10) is provided at both the first working oil port and the second working oil port of the first flow dividing valve (8), and the pressure relief valve (10) is configured to discharge the overpressure oil to the pressure relief oil circuit when the pressure at the connected oil port exceeds a preset threshold; A shuttle valve (9) with two inlets respectively connected to the first oil circuit and the second oil circuit, and an outlet of the shuttle valve (9) is connected to the hydraulic control end of the first flow dividing valve (8); When the control oil output from the outlet of the shuttle valve (9) acts on the hydraulic control end of the first flow dividing valve (8), the first flow dividing valve (8) switches to the first working position. At this time, the inlet of the first flow dividing valve (8) communicates with the first working oil port through a first throttle orifice and with the second working oil port through a second throttle orifice.

2. The hydrostatic synchronous control system for straddle carriers according to claim 1, wherein: Further comprising: A second flow dividing valve (6) with an inlet connected to the first working oil port of the first flow dividing valve (8), a first working oil port connected to the first end of a first motor (51), and a second working oil port connected to the first end of a second motor (52); A third flow dividing valve (7) with an inlet connected to the second working oil port of the first flow dividing valve (8), a first working oil port connected to the first end of a third motor (53), and a second working oil port connected to the first end of a fourth motor (54); The second ends of the first motor (51), the second motor (52), the third motor (53), and the fourth motor (54) are all connected to the second oil circuit upstream of the shuttle valve.

3. The hydrostatic synchronous control system for straddle carriers according to claim 2, wherein: Pressure relief valves (10) are connected to both the first working oil port and the second working oil port of the second flow dividing valve (6), and to both the first working oil port and the second working oil port of the third flow dividing valve (7).

4. The hydrostatic synchronous control system for straddle carriers according to claim 3, wherein: The inlet of the pressure relief valve (10) is connected to the working oil port of the corresponding flow dividing valve, and the outlet of the pressure relief valve (10) is connected to the pressure relief oil circuit; when the pressure at the oil port connected to the inlet of the pressure relief valve (10) does not exceed the preset threshold, the inlet and the outlet of the pressure relief valve (10) are cut off, and when the pressure at the oil port connected to the inlet of the pressure relief valve (10) exceeds the preset threshold, the inlet and the outlet of the pressure relief valve (10) are in communication.

5. The hydrostatic synchronous control system for straddle carriers according to claim 4, characterized in that: The outlet of the shuttle valve (9) is connected in parallel to the hydraulic control ends of the first flow dividing valve (8), the second flow dividing valve (6), and the third flow dividing valve (7) after passing through a reversing valve (19); The reversing valve (19) has a first working position and a second working position. When the reversing valve (19) is in the first working position, the hydraulic control ends of the first flow dividing valve (8), the second flow dividing valve (6), and the third flow dividing valve (7) are in communication with the fuel tank; when the reversing valve (19) is in the second working position, the hydraulic control ends of the first flow dividing valve (8), the second flow dividing valve (6), and the third flow dividing valve (7) are in communication with the outlet of the shuttle valve (9).

6. The hydrostatic synchronous control system for straddle carriers according to claim 1, wherein: Further comprising: A piston cylinder (15) connected to the variable pump (14) for controlling the displacement of the variable pump (14).

7. The hydrostatic synchronous control system for straddle carriers according to claim 6, characterized in that: Both ends of the piston cylinder (15) are respectively connected to the first oil port of the first electro-hydraulic proportional valve and the first oil port of the second electro-hydraulic proportional valve; the second oil ports of the first electro-hydraulic proportional valve and the second electro-hydraulic proportional valve are connected in parallel and then connected to the pressure relief oil circuit; the third oil ports of the first electro-hydraulic proportional valve and the second electro-hydraulic proportional valve are connected in parallel and then connected to an external port through a third oil circuit; by adjusting the spool position and spool opening of the first electro-hydraulic proportional valve and the second electro-hydraulic proportional valve, the position of the piston cylinder (15) can be adjusted to control the displacement of the variable pump (14).

8. The hydrostatic synchronous control system for straddle carriers according to claim 7, characterized in that: It further includes: A pressure cut-off valve (12), whose inlet is connected to the third oil circuit; An energy-saving shuttle valve (13), with two inlets respectively connected to the first oil circuit and the second oil circuit, and an outlet connected to the control end of the pressure cut-off valve (12); When the pressure oil output from the outlet of the energy-saving shuttle valve (13) exceeds a preset threshold and acts on the control end of the pressure cut-off valve (12), the inlet of the pressure cut-off valve (12) is connected to the fuel tank, the piston cylinder (15) maintains its position, and the variable pump (14) outputs flow at a preset minimum displacement.

9. The hydrostatic synchronous control system for straddle carriers according to claim 1, wherein: It further includes: A make-up oil pump (2), coaxially connected to the variable pump (14), and the hydraulic oil output by the make-up oil pump (2) can be unidirectionally conveyed to the first oil circuit and the second oil circuit.

10. A straddle carrier, characterized in that, It includes the hydrostatic synchronous control system for straddle carriers according to any one of claims 1-9.

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