A hydraulic control system, method, and backhoe loader for a flat push loading backhoe loader

Abstract

The application provides a flat pushing loading hydraulic control system and method of a positive shovel excavator and the positive shovel excavator. The flat pushing loading hydraulic control system of the positive shovel excavator comprises a detection module for detecting a target parameter and sending a target signal; a control module receiving the target signal and judging whether a bucket of the positive shovel excavator is in a working node of flat pushing loading based on the target signal; and an overflow valve group in communication with a rodless cavity of a boom cylinder of the positive shovel excavator, wherein the overflow valve group at least comprises high overflow working pressure A and low overflow working pressure B for controlling working pressure of the rodless cavity of the boom cylinder, and system pressure of the positive shovel excavator is C, wherein A≥C>B; wherein when the bucket is in the working node of flat pushing loading, the control module controls the overflow valve group to operate at the low overflow working pressure B, so that when the working pressure of the rodless cavity of the boom cylinder exceeds the low overflow working pressure B, hydraulic oil in the rodless cavity of the boom cylinder overflows, so as to realize automatic falling of the boom.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of engineering vehicles, in particular to a flat-pushing loading hydraulic control system and method of a backhoe excavator and the backhoe excavator. BACKGROUND

[0002] The backhoe working device is commonly used in large or super-large hydraulic excavators. Currently, the backhoe excavator is a combined working device of a boom, a stick, a bucket, and a bucket opening mechanism. When the excavator is flat-pushing loading, it needs to perform several operations in combination, such as pushing out the stick (the piston rod of the stick cylinder is extended) + closing the bucket (the piston rod of the bucket cylinder is extended) + lowering the boom (the piston rod of the boom cylinder is retracted). Especially at the initial stage of loading, the bucket needs to be flat-pushed at a low position to ensure the loading degree of the bucket. Therefore, the realization of the flat-pushing loading function is extremely important for the backhoe excavator.

[0003] During the process of flat-pushing loading of the bucket, the boom is pressed by its own gravity and the gravity of the material, so that the rodless chamber of the boom cylinder bears a high pressure, which causes the boom cylinder to frequently overflow at a high pressure, and the boom cylinder is greatly damaged. In the related art, to avoid the problem of high-pressure overflow of the boom cylinder, the operator needs to adjust the lowering of the boom at any time, which requires the operator to have a high operation level. SUMMARY

[0004] Therefore, the present application provides a flat-pushing loading hydraulic control system and method of a backhoe excavator, which realizes automatic overflow of the boom cylinder at a low overflow pressure, prolongs the service life of the hydraulic element, and improves the loading efficiency. In addition, the present application also provides a flat-pushing loading hydraulic control method of a backhoe excavator including a flat-pushing loading hydraulic control system of the backhoe excavator and the backhoe excavator.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A flat-pushing loading hydraulic control system of a backhoe excavator, comprising:

[0007] A detection module for detecting a target parameter and sending a target signal;

[0008] A control module receiving the target signal and judging whether the bucket of the backhoe excavator is at a working node of flat-pushing loading based on the target signal;

[0009] An overflow valve group in communication with the rodless chamber of the boom cylinder of the backhoe excavator, the overflow valve group including at least a high overflow working pressure A and a low overflow working pressure B for controlling the working pressure of the rodless chamber of the boom cylinder, and the system pressure of the backhoe excavator is C, wherein A≥C>B;

[0010] When the bucket is in the working node of pushing loading, the control module controls the overflow valve group to operate at the low overflow working pressure B, so that when the rodless cavity pressure of the boom cylinder exceeds the low overflow working pressure B, the hydraulic oil in the rodless cavity of the boom cylinder overflows to realize automatic falling of the boom.

[0011] Optionally, in the pushing loading hydraulic control system of the backhoe excavator, the target parameters include the rodless cavity pressure of the stick cylinder of the backhoe excavator, the opening signal of the first valve in the main valve stick joint of the backhoe excavator, and the opening pilot signal of the second valve in the main valve boom joint of the backhoe excavator.

[0012] The first valve is used to control the oil inlet of the rodless cavity of the stick cylinder, and the second valve is used to control the oil inlet of the rodless cavity of the boom cylinder.

[0013] Optionally, in the pushing loading hydraulic control system of the backhoe excavator, the low overflow working pressure B≥D, and D is the maximum pressure value of the rodless cavity of the boom cylinder when the bucket of the backhoe excavator in the full load state is static.

[0014] Optionally, in the pushing loading hydraulic control system of the backhoe excavator, C-B≥3Mpa.

[0015] Optionally, in the pushing loading hydraulic control system of the backhoe excavator, the detection module includes:

[0016] A pressure sensor for acquiring the rodless cavity pressure of the stick cylinder.

[0017] Optionally, in the pushing loading hydraulic control system of the backhoe excavator, the rodless cavity pressure of the stick cylinder is greater than 60% of C, the opening of the first valve is greater than 70%, and the opening pilot signal of the second valve is 0. The control module judges that the bucket is in the working node of pushing loading.

[0018] Optionally, in the pushing loading hydraulic control system of the backhoe excavator, the overflow valve group includes:

[0019] A reversing valve and a liquid-controlled secondary overflow valve connected in series with the reversing valve, the reversing valve being connected with a pilot pump of the backhoe excavator, and the liquid-controlled secondary overflow valve being connected with the rodless cavity of the boom cylinder.

[0020] The reversing valve can be switched between a first working position and a second working position by pilot oil provided by the pilot pump, so that the liquid-controlled secondary overflow valve is switched between the high overflow working pressure A and the low overflow working pressure B.

[0021] Optionally, in the flat-pushing loading hydraulic control system of the backhoe excavator, the overflow valve group comprises an electromagnetic proportional overflow valve, and the electromagnetic proportional overflow valve is capable of switching between the high overflow working pressure A and the low overflow working pressure B.

[0022] A flat-pushing loading hydraulic control method of a backhoe excavator, comprising the following steps:

[0023] detecting target parameters and sending target signals, wherein the target parameters comprise a rodless chamber pressure of a bucket rod cylinder of the backhoe excavator, an opening degree signal of a first valve in a bucket rod joint of a main valve of the backhoe excavator, and an opening degree pilot signal of a second valve in a boom joint of the main valve of the backhoe excavator;

[0024] receiving the target signals and judging whether a bucket of the backhoe excavator is in a working node of flat-pushing loading based on the target signals;

[0025] when the bucket is in the working node of flat-pushing loading, controlling an overflow valve group to operate at a low overflow working pressure B, so that when a rodless chamber pressure of a boom cylinder of the backhoe excavator exceeds the low overflow working pressure B, overflow occurs, and automatic falling of the boom is realized;

[0026] wherein the overflow valve group is in communication with the rodless chamber of the boom cylinder, the overflow valve group comprises at least a high overflow working pressure A and a low overflow working pressure B capable of controlling the rodless chamber working pressure of the boom cylinder, and a system pressure of a hydraulic system is C, wherein A≥C>B.

[0027] The application provides a flat-pushing loading hydraulic control system of a backhoe excavator, comprising an overflow valve group connected to a rodless chamber of a boom cylinder, the overflow valve group enabling the rodless chamber of the boom cylinder to operate at a high overflow working pressure A and a low overflow working pressure B, a system pressure of a hydraulic system being C, wherein A≥C>B; a detection module detecting target parameters and sending target signals; and a control module receiving the target signals and judging whether a bucket is in a working node of flat-pushing loading based on the target signals. If the bucket is in the working node of flat-pushing loading, the overflow valve group operates at the low overflow working pressure B, and when a rodless chamber pressure of the boom cylinder exceeds the low overflow working pressure B, hydraulic oil in the rodless chamber of the boom cylinder overflows, thereby realizing automatic falling of the boom at the low overflow working pressure B, prolonging the service life of hydraulic elements, and improving loading efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only are a part of the present application, and for those skilled in the art, other drawings can be obtained without creative work based on the provided drawings.

[0029] Figure 1 The schematic diagram of the flat pushing loading hydraulic control system of the backhoe excavator provided in the embodiments of the present application.

[0030] Figure 2 The schematic diagram of the main valve boom connection provided in the embodiments of the present application.

[0031] Figure 3 The schematic diagram of the main valve stick connection provided in the embodiments of the present application.

[0032] Figure 4 The structural schematic diagram of the backhoe excavator provided in the embodiments of the present application.

[0033] In Figures 1-4 , the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the accompanying drawings in the following description only are a part of the present application, and for those skilled in the art, other drawings can be obtained without creative work based on the provided drawings.

[0034] 1, control module; 2, bucket cylinder; 3, bucket; 4, boom cylinder; 5, boom; 6, stick cylinder; 7, first valve; 8, second valve; 21, reversing valve; 22, liquid-controlled two-stage overflow valve; 9, pressure sensor; 10, pilot pump; 11, stick; 12, power source; 13, main pump; 14, oil tank; 15, main valve stick connection; 16, main valve boom connection; 17, main overflow valve; 18, third valve; 19, fourth valve. DETAILED DESCRIPTION

[0035] The present application provides a flat pushing loading hydraulic control system of a backhoe excavator, which realizes automatic overflow of the boom cylinder under low overflow pressure, prolongs the service life of the hydraulic element, and improves the loading efficiency. In addition, the present application also provides a flat pushing loading hydraulic control method of a backhoe excavator including the flat pushing loading hydraulic control system of the backhoe excavator and a backhoe excavator.

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0037] The backhoe excavator comprises a swing arm 5, a bucket 3, a bucket arm 11 connecting the swing arm 5 and the bucket 3, a swing arm cylinder 4, a bucket cylinder 2 and a bucket arm cylinder 6 sequentially and respectively driving the swing arm 5, the bucket 3 and the bucket arm 11 to move, under the driving of the swing arm cylinder 4, the bucket cylinder 2 and the bucket arm cylinder 6, the bucket 3 can at least rotate in a horizontal direction, move towards a position close to materials and be lifted or dropped to complete different work tasks. The backhoe excavator drives a main pump 13 to draw hydraulic oil from an oil tank 14 and convert the hydraulic oil into high-pressure hydraulic oil by a power source 12; a pilot pump 10 provides pressure oil for a control circuit to control the output of the main pump 13 and the action of an executing element; a main valve bucket arm connection 15 of the backhoe excavator is connected with the bucket arm cylinder 6 through a hydraulic oil circuit to control the oil inlet of the rodless cavity and the rod cavity of the bucket arm cylinder 6 to realize the pushing out or recovery of the bucket arm 11; and a main valve swing arm connection 16 of the backhoe excavator is connected with the swing arm cylinder 4 through a hydraulic oil circuit to control the oil inlet of the rodless cavity and the rod cavity of the swing arm cylinder 4 to realize the lifting or dropping of the swing arm 5.

[0038] When the backhoe excavator is in a work node of flat pushing loading, the bucket 3 rotates in a clockwise direction under the driving of the bucket cylinder 2, the bucket arm 11 pushes out outward (i.e. towards the position of materials) under the driving of the bucket arm cylinder 6, and the swing arm 5 needs to drop to cooperate with the bucket 3 to complete the flat pushing loading. However, in the prior art, the swing arm 5 often drops with high-pressure overflow, i.e. overflow only occurs when the pressure of the high-pressure section of a port overflow valve, which protects the swing arm cylinder, is exceeded.

[0039] As shown in FIG. 1, Figures 1-4 The embodiment of the present application provides a flat pushing loading hydraulic control system of a backhoe excavator, which comprises a detection module, a control module 1 and an overflow valve group. The overflow valve group comprises a high overflow working pressure A and a low overflow working pressure B, and the overflow valve group is communicated with the rodless cavity of the swing arm cylinder 4 of the backhoe excavator to control the working pressure of the rodless cavity of the swing arm cylinder 4 to be switched between the high overflow working pressure A and the low overflow working pressure B, wherein A≥C>B, and C is the working pressure of the backhoe excavator.

[0040] Specifically, the detection module is used for detecting a target parameter and sending a target signal to the control module 1, the control module 1 judges whether the bucket 3 of the backhoe excavator is in a work node of flat pushing loading based on the target signal, and if so, the controller issues an instruction to switch the overflow valve group to operate at the low overflow working pressure B to make the pressure of the rodless cavity of the swing arm cylinder 4 exceed the low overflow working pressure to cause overflow, thereby realizing the automatic dropping of the swing arm 5 at the low overflow working pressure, prolonging the service life of the hydraulic element, avoiding the frequent operation of the operation lever of the swing arm 5 by the vehicle operator, reducing the operation difficulty of the vehicle operator, making the process of flat pushing loading more smooth and improving the loading efficiency.

[0041] It should be noted that, in general, the high overflow working pressure A is greater than the system pressure C, wherein the high overflow working pressure A is set to protect the safe use of the oil cylinder.

[0042] In an example, the value of the high overflow working pressure A higher than the system pressure C is 2-3 Mpa, wherein A=37 Mpa and C=34 Mpa.

[0043] In actual engineering, the system pressure C of different types of positive shovel excavators has different pressure values. For a positive shovel excavator with a larger system pressure C, in order to better protect the oil cylinder, the difference between the high overflow working pressure A and the system pressure C can be greater than 3 Mpa, and the specific value of the high overflow working pressure A is determined according to the actual situation.

[0044] Further, the target parameters include the rodless chamber pressure of the bucket rod oil cylinder 6 of the positive shovel excavator, the opening signal of the first valve 7 in the main valve bucket rod connection 15 of the positive shovel excavator, and the opening pilot signal of the second valve 8 in the main valve boom connection 16 of the positive shovel excavator; wherein the first valve 7 is used to control the oil inlet of the rodless chamber of the bucket rod oil cylinder 6, and the second valve 8 is used to control the oil inlet of the rodless chamber of the boom oil cylinder 4. When the bucket 3 is in the flat pushing loading working node, the piston rod of the bucket rod oil cylinder 6 is extended, and when the piston rod is extended, the pilot pressure of the bucket rod oil cylinder 6 reaches a specified value (the selection of the value is related to the opening of the first valve 7 and the system pressure of the positive shovel excavator), and the rodless chamber pressure of the bucket rod oil cylinder 6 reaches a specified value (the selection of the value is related to the system pressure) when the bucket is ready to load, and the boom 5 has no lifting action (the piston rod of the boom oil cylinder 4 is not extended in the original state). Through the detection of the above target parameters, the control module 1 can directly judge whether the positive shovel excavator is in the flat pushing loading working node, which is convenient for the rapid response of the system.

[0045] In some other optional embodiments, the target parameters can also be parameters that indirectly feedback whether the bucket 3 is in the flat pushing loading working node, for example, the pressure of the rod chamber of the bucket rod oil cylinder 6 (the rodless chamber pressure is calculated from the pressure), the opening state of the third valve 18 (the third valve 18 is used to control the oil inlet of the rod chamber of the boom oil cylinder 4, and the state of the second valve 8 is derived from the state of the third valve 18), and the opening signal of the fourth valve 19 (the fourth valve 19 is used to control the oil inlet of the rod chamber of the bucket rod oil cylinder 6, and the opening of the first valve 7 is derived from the opening of the fourth valve 19).

[0046] In some optional embodiments, the low overflow working pressure B≥D, and D is the maximum pressure value of the rodless chamber of the boom oil cylinder 4 when the bucket 3 of the positive shovel excavator in the full load state is stationary. In this way, when the positive shovel excavator stops at any position, the bucket 3 is prevented from falling uncontrollably, thereby causing a safety accident. The setting of the low overflow working pressure B≥D improves safety.

[0047] In some optional embodiments, C-B≥3Mpa. That is, the pressure of the positive shovel excavator is at least 3Mpa greater than the low overflow working pressure, so that the rodless chamber pressure of the boom cylinder 4 can overflow at a lower working pressure, further improving the service life of the hydraulic components.

[0048] In some optional embodiments, the detection module includes a pressure sensor 9 for acquiring the rodless chamber pressure of the arm cylinder 6. The pressure sensor 9 can directly acquire the rodless chamber pressure of the arm cylinder 6, improving the detection speed of the detection module.

[0049] In some optional embodiments, the rodless chamber pressure of the arm cylinder 6 is greater than 60% of C, the opening of the first valve 7 is greater than 70%, and the opening pilot signal of the second valve 8 is 0. The control module 1 determines that the bucket 3 is in the flat pushing loading working node. In a certain example, when the positive shovel excavator has no boom lifting action (the lifting pilot pressure is 0), has an arm pushing instruction (the pushing pilot pressure is greater than 20bar), and the rodless chamber pressure of the arm cylinder 6 is greater than 28MPa, the control system determines that the machine is in the flat pushing loading working node.

[0050] It should be noted that the values of the above target parameters are optimal values, and in some systems, the values can also be near the above selected values.

[0051] In some optional embodiments, the overflow valve group includes a directional valve 21 and a pilot-operated secondary overflow valve 22 connected in series with the directional valve 21. The directional valve 21 is connected to the pilot pump 10 of the positive shovel excavator, and the pilot-operated secondary overflow valve 22 is connected to the rodless chamber of the boom cylinder 4. The directional valve 21 can be switched between the first working position and the second working position by the pilot oil provided by the pilot pump 10, so that the pilot-operated secondary overflow valve 22 can be switched between the high overflow working pressure A and the low overflow working pressure B. It can be seen that the composition of the overflow valve group is simple, and the operating principle is simple.

[0052] In some optional embodiments, the overflow valve group is composed of an electromagnetic proportional overflow valve. The electromagnetic proportional overflow valve can be switched between the high overflow working pressure A and the low overflow working pressure B. When the system needs to work at two different pressure stages, the automatic adjustment of the pressure can be realized by changing the current signal input to the electromagnetic proportional overflow valve. The continuous control characteristics of this valve enable it to automatically compensate the target according to the collected information, realize a series of continuously controllable follow-up changes, that is, the selection of the working pressure of the electromagnetic proportional overflow valve is more flexible, which can be adapted to more positive shovel excavators, and improves the practicability of the system.

[0053] In some other optional embodiments, the overflow valve group can also be a pilot-operated secondary overflow valve.

[0054] The application further provides a flat-pushing loading hydraulic control method of the positive shovel excavator, comprising the following steps.

[0055] Detect a target parameter and send a target signal, the target parameter comprising a rodless cavity pressure of a bucket rod cylinder 6 of the positive shovel excavator, an opening degree signal of a first valve 7 in a main valve bucket rod joint 15 of the positive shovel excavator, and an opening degree pilot signal of a second valve 8 in a main valve boom joint 16 of the positive shovel excavator; receive the target signal, and judge whether the bucket 3 of the positive shovel excavator is in a flat-pushing loading working node based on the target signal; when the bucket 3 is in the flat-pushing loading working node, control the overflow valve group to operate at a low overflow working pressure B, so as to cause overflow when the rodless cavity pressure of the boom cylinder 4 of the positive shovel excavator exceeds the low overflow working pressure B, and realize automatic falling of the boom 5; wherein the overflow valve group is in communication with the rodless cavity of the boom cylinder 4, the overflow valve group at least comprises a high overflow working pressure A and a low overflow working pressure B capable of controlling the working pressure of the rodless cavity of the boom cylinder 4, and the system pressure of the hydraulic system is C, wherein A≥C>B.

[0056] The basic principle of the application is described above in combination with specific embodiments, but it should be pointed out that the advantages, advantages, effects and the like mentioned in the application are only examples and not limitations, and these advantages, advantages, effects and the like cannot be considered as the necessary possession of each embodiment of the application. In addition, the above specific details disclosed are only for the purpose of example and for the purpose of understanding, and are not limited to the application which must be implemented with the above specific details.

[0057] The block diagrams of the devices, apparatuses, equipment, systems involved in the application are only illustrative examples and are not intended to require or imply the connection, arrangement and configuration shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, equipment, systems can be connected, arranged and configured in any way. Words such as "include", "contain", "have" and the like are open-ended words, which mean "including but not limited to", and can be used interchangeably. The words "or" and "and" used herein mean the word "and / or", and can be used interchangeably unless the context clearly indicates otherwise. The word "such as" used herein means the phrase "such as but not limited to", and can be used interchangeably.

[0058] It should also be noted that in the devices, equipment and methods of the application, each component or each step can be decomposed and / or recombined. These decompositions and / or recombination should be considered as equivalent solutions of the application.

[0059] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other aspects without departing from the scope of the application. Thus, the present application is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0060] It should be understood that the limiting words "first", "second", "third", "fourth", "fifth" and "sixth" used in the embodiments description of the present application are only used for more clearly describing the technical solutions, and cannot be used to limit the protection scope of the present application.

[0061] The above description has been presented for the purpose of illustration and description. Furthermore, this description is not intended to limit the embodiments of the application to the forms disclosed herein. Although several example aspects and embodiments have been discussed above, those of ordinary skill in the art will appreciate a variety of modifications, alternatives, permutations, additions, and sub-combinations of the described aspects and embodiments.

Claims

1. A hydraulic control system for a flat push loading system of a positive shovel characterized by, Comprising: a detection module for detecting target parameters and sending target signals, the target parameters including a rodless chamber pressure of a bucket rod cylinder of the backhoe excavator, an opening degree signal of a first valve in a bucket rod joint of a main valve of the backhoe excavator, and an opening degree pilot signal of a second valve in a boom joint of the main valve of the backhoe excavator; a control module receiving the target signals and determining whether a bucket of the backhoe excavator is in a work node of pushing loading based on the target signals; an overflow valve group in communication with a rodless chamber of a boom cylinder of the backhoe excavator, the overflow valve group including at least a high overflow working pressure A and a low overflow working pressure B for controlling a working pressure of the rodless chamber of the boom cylinder, and a system pressure C of the backhoe excavator, wherein A≥C>B; wherein, when the bucket is in the work node of pushing loading, the control module controls the overflow valve group to operate at the low overflow working pressure B, so that when the rodless chamber pressure of the boom cylinder exceeds the low overflow working pressure B, hydraulic oil in the rodless chamber of the boom cylinder overflows to realize automatic falling of the boom; the control module determining whether the bucket of the backhoe excavator is in the work node of pushing loading based on the target signals, comprising: when the rodless chamber pressure of the bucket rod cylinder is greater than 60% of C, the opening degree of the first valve is greater than 70%, and the opening degree pilot signal of the second valve is 0, the control module determines that the bucket is in the work node of pushing loading; or when the boom lifting pilot pressure of the backhoe excavator is 0, the bucket rod pushing pilot pressure is greater than 20 bar, and the rodless chamber pressure of the bucket rod cylinder is greater than 28 MPa, the control module determines that the bucket is in the work node of pushing loading.

2. The flat-pushing loading hydraulic control system of a positive shovel according to claim 1, characterized by, The first valve is used for controlling oil inlet of the rodless chamber of the bucket rod cylinder, and the second valve is used for controlling oil inlet of the rodless chamber of the boom cylinder.

3. The flat-pushing loading hydraulic control system of a positive shovel according to Claim 1, wherein The low overflow working pressure B≥D, and D is a maximum pressure value of the rodless chamber of the boom cylinder when the bucket of the backhoe excavator in a full load state is stationary.

4. The flat-pushing loading hydraulic control system of a positive shovel according to Claim 1, wherein C-B≥3Mpa.

5. The flat-pushing loading hydraulic control system of a positive shovel according to Claim 2, wherein The detection module comprises: a pressure sensor for acquiring the rodless chamber pressure of the bucket rod cylinder.

6. The flat-pushing loader hydraulic control system of the positive shovel according to claim 1, characterized by, The overflow valve group comprises: a reversing valve and a liquid-controlled secondary overflow valve connected in series with the reversing valve, the reversing valve being connected with a pilot pump of the backhoe excavator, and the liquid-controlled secondary overflow valve being connected with the rodless chamber of the boom cylinder; wherein, through pilot oil provided by the pilot pump, the reversing valve can be switched between a first working position and a second working position to switch the liquid-controlled secondary overflow valve between the high overflow working pressure A and the low overflow working pressure B.

7. The flat-pushing loader hydraulic control system of the positive shovel according to claim 1, characterized by, The overflow valve group comprises an electromagnetic proportional overflow valve capable of being switched between the high overflow working pressure A and the low overflow working pressure B.

8. A hydraulic control method of a flat push loading of a positive shovel, characterized by, The method comprises the following steps: detecting target parameters and sending target signals, the target parameters including a rodless chamber pressure of a bucket rod cylinder of the backhoe excavator, an opening degree signal of a first valve in a bucket rod joint of a main valve of the backhoe excavator, and an opening degree pilot signal of a second valve in a boom joint of the main valve of the backhoe excavator; Receiving the target signal, and determining whether the bucket of the front shovel excavator is in a work node of pushing loading based on the target signal; When the bucket is in the work node of pushing loading, controlling a group of overflow valves to operate at a low overflow working pressure B, so as to cause overflow when a rodless cavity pressure of a boom cylinder of the front shovel excavator exceeds the low overflow working pressure B, and realize automatic falling of the boom; The group of overflow valves is communicated with the rodless cavity of the boom cylinder, and the group of overflow valves at least includes a high overflow working pressure A and a low overflow working pressure B capable of controlling the working pressure of the rodless cavity of the boom cylinder, and a system pressure of the front shovel excavator is C, wherein A≥C>B; The method for determining whether the bucket of the front shovel excavator is in the work node of pushing loading based on the target signal comprises: When the rodless cavity pressure of the stick cylinder is greater than 60% of C, the opening of the first valve is greater than 70%, and the opening pilot signal of the second valve is 0, the control module determines that the bucket is in the work node of pushing loading; or When the boom lifting pilot pressure of the front shovel excavator is 0, the stick pushing pilot pressure is greater than 20 bar, and the rodless cavity pressure of the stick cylinder is greater than 28 MPa, the control module determines that the bucket is in the work node of pushing loading.

9. A positive shovel characterized by comprising: The pushing loading hydraulic control system of the front shovel excavator comprises the front shovel excavator according to any one of claims 1-7.

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