Hydraulic system of dozer blade of excavator and control method

Abstract

The invention provides a hydraulic system of a bulldozing blade of an excavator and a control method. The hydraulic system comprises a main pump, a main valve group, a bulldozing oil cylinder and a bidirectional balance valve, the main valve set comprises a bulldozing valve, a linear walking valve, a left walking valve, a right walking valve, a first middle-position stop valve and a second middle-position stop valve. The main valve set is provided with a first oil supply port and a second oil supply port, and the second oil supply port is connected with the right walking valve and further connected with the linear walking valve. The first oil supply port is connected with the linear walking valve; the linear walking valve is connected with the left walking valve; the linear walking valve is connected with the bulldozing valve and is also connected with the second middle-position stop valve; two oil ports of the right walking valve are used for being connected with a right walking motor respectively, the right walking valve is connected with the second middle-position stop valve, two oil ports of the left walking valve are used for being connected with a left walking motor respectively, and the left walking valve is connected with the first middle-position stop valve. The dozer blade can be prevented from falling off suddenly, and deviation occurring when dozer blade and walking composite actions are executed is avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of engineering machinery hydraulics, and in particular to a hydraulic system and a control method for a bulldozer of an excavator. Background Art

[0002] With the development and growth of the excavator market, the application of excavators is becoming more and more common, and the working conditions are becoming more and more diverse. The bulldozer has become one of the most frequently used auxiliary tools of the excavator; but the current bulldozer control method is prone to sudden falling and deviation when the bulldozer and walking are used in a compound action at the same time.

[0003] Therefore, there is an urgent need for a hydraulic system and control method for an excavator bulldozer, which can prevent the bulldozer from falling suddenly and avoid deviation when performing a combined action of bulldozing and walking. Summary of the invention

[0004] The purpose of the present invention is to provide a hydraulic system and control method for an excavator bulldozer, aiming to solve the technical problems that the traditional bulldozer hydraulic control method is prone to sudden falling and deviation when performing complex actions.

[0005] To achieve the above-mentioned object, in a first aspect, the present invention provides a hydraulic system for an excavator bulldozer, comprising: a main pump, a main valve group connected to the main pump, a bulldozer cylinder connected to the main valve group, and a two-way balancing valve arranged between the main valve group and the bulldozer cylinder;

[0006] The main valve group includes a bulldozer valve for controlling the lifting / lowering of the bulldozer cylinder, a linear travel valve for controlling the linear travel required in a compound action, a left travel valve for controlling the left travel motor of the excavator, a right travel valve for controlling the excavator to travel to the right, and a first mid-position cut-off valve and a second mid-position cut-off valve; the main valve group is provided with a first oil supply port and a second oil supply port connected to the main pump; the two-way balance valve includes a first one-way balance valve and a second one-way balance valve which are mutually pilot-controlled;

[0007] The second oil supply port is connected to the sixth oil port and the seventh oil port of the right travel valve, and is also connected to the third oil port of the linear travel valve;

[0008] The first oil supply port is connected to the fourth oil port of the linear travel valve;

[0009] The second oil port of the linear travel valve is connected to the sixth oil port and the seventh oil port of the left travel valve;

[0010] The first oil port of the linear travel valve is connected to the fourth oil port of the bulldozer valve, and is also connected to the second oil port of the second mid-position cut-off valve;

[0011] The first oil port and the second oil port of the right travel valve are respectively used to connect with the two working oil ports of the right travel motor, the third oil port of the right travel valve is connected with the second oil port of the second middle cut-off valve, and the first oil port of the second middle cut-off valve is connected with the third oil port of the bulldozer valve.

[0012] The third oil port and the fourth oil port of the left travel valve are respectively used to connect with the two working oil ports of the left travel motor, the second oil port of the left travel valve is connected with the second oil port of the first middle cut-off valve, and the first oil port of the first middle cut-off valve is connected with the second oil port of the bulldozer valve.

[0013] The first oil port of the bulldozer valve is connected to the conducting end of the first one-way balancing valve, and the conducting end away from the conducting end of the first one-way balancing valve is connected to the rodless chamber of the bulldozer cylinder; the second oil port of the bulldozer valve is connected to the conducting end of the second one-way balancing valve, and the conducting end away from the conducting end of the second one-way balancing valve is connected to the rod chamber of the bulldozer cylinder.

[0014] As a further improvement of the above scheme, the hydraulic system further includes a pilot control handle, a shuttle valve is further provided in the main valve group, and a plurality of pilot oil ports are further provided on the valve block of the main valve group;

[0015] The bulldozer valve, the linear travel valve, the left travel valve, the right travel valve, the first center cut-off valve and the second center cut-off valve are all pilot hydraulically controlled valves;

[0016] The pilot control handle has a first pilot oil port and a second pilot oil port, the first pilot oil port is connected to the first pilot oil port of the bulldozer valve and is also connected to the first oil port of the shuttle valve;

[0017] The second pilot oil port is connected to the second pilot oil port of the bulldozer valve and is also connected to the second oil port of the shuttle valve;

[0018] The third oil port of the shuttle valve is connected to the pilot oil ports of the first center cut-off valve and the second center cut-off valve respectively, and is also connected to the pilot oil port of the linear travel valve through the first non-return valve;

[0019] The first pilot oil port and the second pilot oil port of the left travel valve are respectively connected to the pilot oil port on the valve block;

[0020] The first pilot oil port and the second pilot oil port of the right travel valve are respectively connected to the pilot oil ports on the valve block.

[0021] As a further improvement of the above scheme, the fifth oil port of the right travel valve is connected to the oil return circuit, and the fourth oil port and the eighth oil port thereof are respectively connected to the pilot oil port on the valve block;

[0022] The eighth oil port of the left travel valve is connected to the oil return circuit, and the fifth oil port and the first oil port of the left travel valve are respectively connected to the pilot oil port on the valve block.

[0023] As a further improvement of the above scheme, the main valve group also includes a main overflow valve, the first oil supply port is connected to the main overflow valve through a second one-way valve, and the second oil supply port is connected to the main overflow valve through a third one-way valve.

[0024] As a further improvement of the above scheme, the bulldozer valve is a mid-position three-position four-way valve;

[0025] The linear travel valve is a two-position four-way valve;

[0026] The left travel valve and the right travel valve are both mid-position three-position eight-way valves;

[0027] The first center cut-off valve and the second center cut-off valve are both two-position two-way valves.

[0028] As a further improvement of the above scheme, the first oil port of the two-way balancing valve is connected to the conducting end of the first one-way balancing valve, and the third oil port of the two-way balancing valve is connected to the conducting end away from the first one-way balancing valve.

[0029] The second oil port of the two-way balancing valve is connected to the conducting end of the second one-way balancing valve, and the fourth oil port of the two-way balancing valve is connected to the far-from conducting end of the second one-way balancing valve;

[0030] Preferably, the first one-way balancing valve comprises a fourth one-way valve and a first pilot relief valve connected in parallel;

[0031] The second one-way balancing valve includes a fifth one-way valve and a second pilot relief valve connected in parallel, and the first pilot relief valve and the second pilot relief valve are in staggered pilot control connection with each other.

[0032] As a further improvement of the above scheme, a multi-three-way valve is also arranged between the pilot control handle and the main valve group, and the multi-three-way valve is provided with a first pressure sensor and a second pressure sensor, which are respectively used to monitor the pilot pressure so as to control the oil supply channel of the main pump through the first oil supply port and / or the second oil supply port.

[0033] In a second aspect, the present invention further provides a method for controlling a hydraulic system of an excavator bulldozer as provided in the first aspect, the steps of which include:

[0034] When the bulldozer is lowered:

[0035] The main pump makes the high-pressure oil flow through the second oil supply port, through the right travel valve in sequence, and then enters the fourth oil port of the bulldozer valve, and flows out from the first oil port of the bulldozer valve and enters the first one-way balance valve of the two-way balance valve, and then enters the rodless chamber of the bulldozer cylinder to lower the bulldozer blade, and at the same time, the overflow valve of the second one-way balance valve, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank;

[0036] When the bulldozer is raised:

[0037] The main pump makes the high-pressure oil flow through the second oil supply port, through the right travel valve, and then into the fourth oil port of the bulldozer valve, and then flows out from the second oil port of the bulldozer valve and enters the second one-way balance valve of the two-way balance valve, and then enters the rod chamber of the bulldozer cylinder to lift the bulldozer blade, and at the same time, the overflow valve of the first one-way balance valve, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank;

[0038] When the bulldozer is lowered and moves in a straight line:

[0039] The main pump supplies high-pressure oil to the sixth oil port of the right travel valve through the second oil supply port, and then to the working oil port of the right travel motor through its second oil port; at the same time, the main pump supplies high-pressure oil to the third oil port of the linear travel valve through the second oil supply port, and then to the seventh oil port of the left travel valve through its second oil port, and then to the working oil port of the left travel motor through its fourth oil port;

[0040] The main pump passes the high-pressure oil through the first oil supply port into the fourth oil port of the linear travel valve, and then into the fourth oil port of the bulldozer valve through its first oil port, and flows out from the first oil port of the bulldozer valve into the first one-way balancing valve of the two-way balancing valve, and then into the rodless chamber of the bulldozer cylinder to lower the bulldozer blade, and at the same time, the overflow valve of the second one-way balancing valve, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank;

[0041] When the bulldozer is lifted and moves in a straight line:

[0042] The main pump supplies high-pressure oil to the sixth oil port of the right travel valve through the second oil supply port, and then to the working oil port of the right travel motor through its second oil port; at the same time, the main pump supplies high-pressure oil to the third oil port of the linear travel valve through the second oil supply port, and then to the seventh oil port of the left travel valve through its second oil port, and then to the working oil port of the left travel motor through its fourth oil port;

[0043] The main pump sends high-pressure oil into the fourth oil port of the linear travel valve through the first oil supply port, and then into the fourth oil port of the bulldozer valve through its first oil port. After flowing out from the second oil port of the bulldozer valve, it enters the second one-way balancing valve of the two-way balancing valve, and then enters the rod chamber of the bulldozer cylinder to lift the bulldozer. At the same time, the overflow valve of the first one-way balancing valve, which is pilot-controlled to each other, opens to flow in the reverse direction and returns to the oil tank.

[0044] As a further improvement of the above scheme, before the main pump supplies oil, the valve core of each valve moves to the corresponding working position under the action of the pilot control oil;

[0045] When the bulldozer is lowered:

[0046] Under the pressure of the pilot control oil, the valve core of the first pilot oil port of the bulldozer valve moves to the right; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off;

[0047] When the bulldozer is raised:

[0048] Under the pressure of the pilot control oil, the valve core of the second pilot oil port of the bulldozer valve moves to the left; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off;

[0049] When the bulldozer is lowered and moves in a straight line:

[0050] Under the pressure of the pilot control oil, the valve core of the first pilot oil port of the bulldozer valve moves to the right; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off;

[0051] The valve core of the second pilot oil port of the right travel valve moves to the left under the pressure of the pilot control oil, and the valve core of the first pilot oil port of the left travel valve moves to the right under the pressure of the pilot control oil;

[0052] When the bulldozer is lifted and moves in a straight line:

[0053] Under the pressure of the pilot control oil, the valve core of the second pilot oil port of the bulldozer valve moves to the left; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off;

[0054] The valve core of the second pilot oil port of the right travel valve moves to the left under the pressure of the pilot control oil, and the valve core of the first pilot oil port of the left travel valve moves to the right under the pressure of the pilot control oil.

[0055] Since the present invention adopts the above technical solution, the beneficial effects of this application are:

[0056] The present invention provides a hydraulic system of an excavator bulldozer, wherein a two-way balancing valve is arranged between a main valve group and a bulldozer oil cylinder, and the two-way balancing valve comprises a first one-way balancing valve and a second one-way balancing valve which are mutually pilot controlled, the first one-way balancing valve is arranged between the bulldozer valve and a rodless chamber of the bulldozer oil cylinder, and the second one-way balancing valve is arranged between the bulldozer valve and a rod chamber of the bulldozer oil cylinder, and by arranging the first one-way balancing valve and the second one-way balancing valve which are mutually pilot controlled, it is possible to prevent the bulldozer oil cylinder from losing control of movement and preventing the oil cylinder from falling suddenly, and at the same time, the two-way balancing valve can also enable the bulldozer oil cylinder to realize a pressure-maintaining function, so that the excavator can continue to perform bulldozing operations;

[0057] In addition, the hydraulic system of the present invention is also provided with a linear travel valve, a shuttle valve, and a first one-way valve connected to the third oil port of the shuttle valve. When the excavator needs to perform a linear travel and bulldozer combined action, after the pilot control oil is turned on, the shuttle valve and the first one-way valve conduct the corresponding channels under the corresponding pilot pressure, so that the valve cores of the linear travel valve, the left travel valve and the right travel valve move to the corresponding working positions, thereby ensuring that the bulldozer and linear travel combined actions can be performed normally;

[0058] Adding the first one-way valve at the pilot oil port PTa of the linear travel valve can also simultaneously meet one or any two of the four actions of boom, arm, bucket, rotation, or compound actions. When operating the travel action at the same time, it ensures that the pilot pressure can push the valve core of the linear travel valve to ensure that the excavator moves in a straight line without deviation. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0060] Figure 1 A schematic diagram of a hydraulic system of an excavator bulldozer disclosed in the present invention;

[0061] Figure 2 for Figure 1 A local enlarged schematic diagram of the I direction;

[0062] Figure 3 for Figure 1 A local enlarged schematic diagram of the J direction;

[0063] Figure 4 for Figure 1 Schematic diagram of a partial enlargement in the K direction.

[0064] Reference numerals:

[0065] 1. Main pump; 2. Main valve group; 21. Bulldozer valve; 22. Linear travel valve; 23. Left travel valve; 24. Right travel valve; 25. First center cut-off valve; 26. Second center cut-off valve; 27. Shuttle valve; 28. Main overflow valve; 29. ​​First check valve;

[0066] 3. Bulldozer cylinder; 4. Two-way balancing valve; 41. First one-way balancing valve; 411. Fourth one-way valve; 412. First pilot relief valve; 42. Second one-way balancing valve; 421. Fifth one-way valve; 422. Second pilot relief valve;

[0067] 5. Pilot control handle; 6. Second one-way valve; 7. Third one-way valve; 8. Multi-connected three-way valve; 81. First pressure sensor; 82. Second pressure sensor;

[0068] P1, first fuel supply port; P2, second fuel supply port.

[0069] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with the implementation methods and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0070] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0071] It should be noted that all directional indications (such as up, down, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0072] In addition, in the present invention, the descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0073] Furthermore, the technical solutions between the various embodiments of the present invention may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in the field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0074] Embodiment 1:

[0075] See also Figure 1-Figure 4 The present invention provides a hydraulic system for an excavator bulldozer, comprising: a main pump 1, a main valve group 2 connected to the main pump 1, a bulldozer cylinder 3 connected to the main valve group 2, and a two-way balance valve 4 arranged between the main valve group 2 and the bulldozer cylinder 3;

[0076] The main valve group 2 includes a bulldozer valve 21 for controlling the lifting / lowering of the bulldozer cylinder 3, a linear travel valve 22, a left travel valve 23 for controlling the left travel motor of the excavator, a right travel valve 24 for controlling the excavator to travel to the right, and a first mid-position cut-off valve 25 and a second mid-position cut-off valve 26; the main valve group 2 is provided with a first oil supply port P1 and a second oil supply port P2 connected to the main pump 1; the two-way balance valve 4 includes a first one-way balance valve 41 and a second one-way balance valve 42 which are mutually pilot-controlled;

[0077] Specifically, in this embodiment, the bulldozer valve 21 is a mid-position three-position four-way valve; the linear travel valve 22 is a two-position four-way valve; the left travel valve 23 and the right travel valve 24 are both mid-position three-position eight-way valves;

[0078] The first center cut-off valve 25 and the second center cut-off valve 26 are both two-position two-way valves;

[0079] The second oil supply port P2 is connected to the sixth oil port and the seventh oil port of the right travel valve 24, and is also connected to the third oil port of the linear travel valve 22;

[0080] The first oil supply port P1 is connected to the fourth oil port of the linear travel valve 22;

[0081] The second oil port of the linear travel valve 22 is connected to the sixth oil port and the seventh oil port of the left travel valve 23;

[0082] The first oil port of the linear travel valve 22 is connected to the fourth oil port of the bulldozer valve 21 and is also connected to the second oil port of the second mid-position cut-off valve 26;

[0083] The first oil port and the second oil port of the right travel valve 24 are respectively used to connect with the two working oil ports of the right travel motor, the third oil port of the right travel valve 24 is connected with the second oil port of the second middle cut-off valve 26, and the first oil port of the second middle cut-off valve 26 is connected with the third oil port of the bulldozer valve 21.

[0084] The third oil port and the fourth oil port of the left travel valve 23 are respectively used to connect with the two working oil ports of the left travel motor, the second oil port of the left travel valve 23 is connected with the second oil port of the first middle cut-off valve 25, and the first oil port of the first middle cut-off valve 25 is connected with the second oil port of the bulldozer valve 21.

[0085] The first oil port of the bulldozer valve 21 is connected to the conducting end of the first one-way balancing valve 41, and the conducting end away from the first one-way balancing valve 41 is connected to the rodless chamber of the bulldozer cylinder 3; the second oil port of the bulldozer valve 21 is connected to the conducting end of the second one-way balancing valve 42, and the conducting end away from the second one-way balancing valve 42 is connected to the rod chamber of the bulldozer cylinder 3; the first oil port of the two-way balancing valve 4 is connected to the conducting end of the first one-way balancing valve 41, the third oil port of the two-way balancing valve 4 is connected to the conducting end away from the first one-way balancing valve 41, the second oil port of the two-way balancing valve 4 is connected to the conducting end of the second one-way balancing valve 42, and the fourth oil port of the two-way balancing valve 4 is connected to the conducting end away from the second one-way balancing valve 42;

[0086] The first one-way balancing valve 41 includes a fourth one-way valve 411 and a first pilot relief valve 412 connected in parallel;

[0087] The second one-way balancing valve 42 comprises a fifth one-way valve 421 and a second pilot relief valve 422 connected in parallel, and the first pilot relief valve 412 and the second pilot relief valve 422 are mutually staggered pilot control connected;

[0088] In the present invention, a two-way balancing valve 4 is arranged between the main valve group 2 and the bulldozer cylinder 3, and the two-way balancing valve 4 includes a first one-way balancing valve 41 and a second one-way balancing valve 42 which are mutually pilot controlled. The first one-way balancing valve 41 is arranged between the bulldozer valve 21 and the rodless chamber of the bulldozer cylinder 3, and the second one-way balancing valve 42 is arranged between the bulldozer valve 21 and the rod chamber of the bulldozer cylinder 3. By arranging the first one-way balancing valve 41 and the second one-way balancing valve 42 which are mutually pilot controlled, it is possible to prevent the bulldozer cylinder 3 from moving out of control and prevent the cylinder from falling suddenly. At the same time, the two-way balancing valve 4 can also enable the bulldozer cylinder 3 to realize the pressure maintaining function, so that the excavator can continue to perform bulldozing operations.

[0089] In addition, the hydraulic system of the present invention is also provided with a linear travel valve 22, a shuttle valve 27, and a first one-way valve 29 connected to the third oil port of the shuttle valve 27. When the excavator needs to perform a combined action of linear travel and bulldozer, after the pilot control oil is turned on, the shuttle valve 27 and the first one-way valve 29 conduct the corresponding channels under the corresponding pilot pressure, so that the valve cores of the linear travel valve 22, the left travel valve 23 and the right travel valve 24 move to the corresponding working positions, thereby ensuring that the combined action of bulldozer and linear travel can be carried out normally without deviation.

[0090] As a preferred embodiment, the hydraulic system further includes a pilot control handle 5, a shuttle valve 27 is further provided in the main valve group 2, and a plurality of pilot oil ports (such as XBtr, XAtr, XBtl, XAtl, etc.) are further provided on the valve block of the main valve group 2;

[0091] The bulldozer valve 21, the linear travel valve 22, the left travel valve 23, the right travel valve 24, the first center cut-off valve 25 and the second center cut-off valve 26 are all pilot hydraulically controlled valves;

[0092] The pilot control handle 5 has a first pilot oil port and a second pilot oil port, wherein the first pilot oil port is connected to the first pilot oil port of the bulldozer valve 21 and is also connected to the first oil port of the shuttle valve 27;

[0093] The second pilot oil port is connected to the second pilot oil port of the bulldozer valve 21 and is also connected to the second oil port of the shuttle valve 27;

[0094] The third oil port of the shuttle valve 27 is connected to the pilot oil ports of the first center cut-off valve 25 and the second center cut-off valve 26 respectively, and is also connected to the pilot oil port of the linear travel valve 22 through the first check valve 29;

[0095] The first pilot oil port and the second pilot oil port of the left travel valve 23 are respectively connected to the pilot oil port on the valve block;

[0096] The first pilot oil port and the second pilot oil port of the right travel valve 24 are respectively connected to the pilot oil port on the valve block;

[0097] The fifth oil port of the right travel valve 24 is connected to the oil return circuit, and the fourth oil port and the eighth oil port thereof are respectively connected to the pilot oil ports on the valve block;

[0098] The eighth oil port of the left travel valve 23 is connected to the oil return circuit, and the fifth oil port and the first oil port thereof are respectively connected to the pilot oil port on the valve block;

[0099] Specifically, the bulldozer valve 21 has three working positions, a lowering working position, a bulldozer middle position, and a lifting working position. In the bulldozer middle position, the four oil ports are not connected to each other. In the lowering working position, the first oil port is connected to the fourth oil port, and the second oil port is connected to the third oil port.

[0100] The first center cut-off valve 25 and the second center cut-off valve 26 have the same structure, and have a connecting working position and a cutting working position respectively. In the connecting working position, the first oil port and the second oil port are connected, and in the switching working position, the first oil port and the second oil port are not connected to each other;

[0101] See also Figure 2-Figure 4 The linear travel valve 22 has a first working position and a second working position. In the first working position, the first oil port is connected to the fourth oil port, and the second oil port is connected to the third oil port. In the second working position, the first oil port is connected to the third oil port, and the second oil port is connected to the fourth oil port.

[0102] The right travel valve 24 has a first working position, a middle position and a second working position. When in the middle position, its first oil port and its second oil port are both connected to its fifth oil port, and the fifth oil port is connected to the oil tank, its third oil port is connected to its seventh oil port, its fourth oil port is connected to its eighth oil port, and its sixth oil port is not connected to the other oil ports;

[0103] When only the bulldozer is in motion, the right travel valve 24 is in the middle position;

[0104] In the first working position, its first oil port is connected with its sixth oil port, its second oil port is connected with its fifth oil port, and its third oil port, its seventh oil port, its fourth oil port and its eighth oil port are not connected with each other;

[0105] In the second working position, its first oil port is connected with its fifth oil port, its second oil port is connected with its sixth oil port, and its third oil port, its seventh oil port, its fourth oil port and its eighth oil port are not connected with each other;

[0106] The left travel valve 23 has a first working position, a middle position and a second working position. When in the middle position, its third oil port and its fourth oil port are both connected to its eighth oil port, and the eighth oil port is connected to the oil tank, its second oil port is connected to its sixth oil port, its first oil port is connected to its fifth oil port, and its seventh oil port is not connected to the other oil ports;

[0107] When only the bulldozer is in motion, the left travel valve 23 is in the middle position;

[0108] In the first working position, its third oil port is connected with its eighth oil port, its fourth oil port is connected with its seventh oil port, and its first oil port, its second oil port, its fifth oil port and its sixth oil port are not connected with each other;

[0109] In the second working position, its third oil port is connected with its seventh oil port, its fourth oil port is connected with its eighth oil port, and its first oil port, its second oil port, its fifth oil port and its sixth oil port are not connected with each other;

[0110] When the excavator moves forward or backward, the pilot control oil pushes the valve core to move to the corresponding working position;

[0111] A multi-way valve 8 is also arranged between the pilot control handle 5 and the main valve group 2. The multi-way valve 8 is provided with a first pressure sensor 81 and a second pressure sensor 82, which are respectively used to monitor the pilot pressure so as to control the oil supply channel of the main pump 1 through the first oil supply port P1 and / or the second oil supply port P2.

[0112] As a further improvement of the above scheme, the main valve group 2 also includes a main overflow valve 28. The first oil supply port P1 is connected to the main overflow valve 28 through the second one-way valve 6, and the second oil supply port P2 is connected to the main overflow valve 28 through the third one-way valve 7. Specifically, in the present embodiment, the main overflow valve 28 is a pilot overflow valve. The setting of the main overflow valve 28 can maintain the pressure in the hydraulic system, stabilize the pressure, and avoid accidents. The one-way valve is connected to the two oil supply ports to further ensure the stability of the pressure in the system.

[0113] Embodiment 2:

[0114] The present invention also provides a control method for a hydraulic system of an excavator bulldozer as provided in Example 1, the steps of which include:

[0115] When the bulldozer is lowered:

[0116] Push the pilot control handle 5 forward, and the valve core of the first pilot oil port of the bulldozer valve 21 moves to the right (to the lowering working position) under the pressure of the pilot control oil; at the same time, the pilot control oil flows through the shuttle valve 27 and the first check valve 29 in sequence to push the valve core of the linear travel valve 22 to move to the right (to the first working position); at this time, the valve core XBp1 of the first mid-position cut-off valve 25 connected to the pilot oil port PTa moves to the left (to the cut-off working position), and the valve core XBp2 of the second mid-position cut-off valve 26 moves to the right (to the cut-off working position), realizing mid-position cut-off;

[0117] The first pressure sensor 81 on the multi-connected three-way valve 8 monitors the pilot pressure, and sends out an electrical signal to control the main pump 1 to supply oil to the second oil supply port P2 through the controller; the main pump 1 allows the high-pressure oil to flow through the second oil supply port P2, through the right travel valve 24 in sequence, and then enter the fourth oil port of the bulldozer valve 21, and then flow out from the first oil port of the bulldozer valve 21 and enter the first one-way balance valve 41 of the two-way balance valve 4, and then enter the rodless chamber of the bulldozer cylinder 3 to lower the bulldozer shovel, and at the same time, the overflow valve of the second one-way balance valve 42, which is pilot-controlled to each other, opens and flows in the reverse direction and then returns to the oil tank; specifically, the high-pressure oil flows into the first one-way balance valve 4 of the two-way balance valve 4. The oil port flows into the rodless chamber of the bulldozer cylinder 3 through the fourth one-way valve 411 and the third oil port of the two-way balance valve 4, maintaining the load to prevent reverse movement. The piston rod of the bulldozer cylinder 3 pushes the bulldozer blade downward, and at the same time, when the pilot pressure is applied to the second pilot relief valve 422 in the cross pilot oil circuit, the second pilot relief valve 422 opens to achieve reverse flow and return to the oil tank; in this arrangement, the high-pressure oil entering the rodless chamber is used as the pilot control oil of the second pilot relief valve 422. After the second pilot relief valve 422 is opened, the hydraulic oil can be slowly returned through the adjustment of the pilot pressure, thereby preventing the bulldozer cylinder 3 from falling suddenly;

[0118] When the bulldozer is raised:

[0119] Push the pilot control handle 5 to move backward, and the valve core of the second pilot oil port of the bulldozer valve 21 moves to the left (to the lifting working position) under the pressure of the pilot control oil; at the same time, the pilot control oil flows through the shuttle valve 27 and the first check valve 29 in sequence to push the valve core of the linear travel valve 22 to move to the right (to the first working position); at this time, the valve core XBp1 of the first mid-position cut-off valve 25 connected to the pilot oil port PTa moves to the left (to the cut-off working position), and the valve core XBp2 of the second mid-position cut-off valve 26 moves to the right (to the cut-off working position), realizing mid-position cut-off;

[0120] The second pressure sensor 82 on the multi-connected three-way valve 8 monitors the pilot pressure and sends out an electrical signal to control the main pump 1 to supply oil to the second oil supply port P2 through the controller; the main pump 1 allows the high-pressure oil to flow through the second oil supply port P2 through the right travel valve 24 and then enter the fourth oil port of the bulldozer valve 21, and then flow out from the second oil port of the bulldozer valve 21 and enter the second one-way balance valve 42 of the two-way balance valve 4, and then enter the rod chamber of the bulldozer cylinder 3 to lift the bulldozer blade, and at the same time, the overflow valve of the first one-way balance valve 41, which is mutually pilot-controlled, opens to flow in the reverse direction and returns to the oil tank;

[0121] Specifically, the high-pressure oil flows into the second oil port of the two-way balance valve 4, passes through the fifth one-way valve 421, and flows into the rod chamber of the bulldozer cylinder 3 via the fourth oil port of the two-way balance valve 4, so as to maintain the load and prevent reverse movement. The piston rod of the bulldozer cylinder 3 retracts and the bulldozer is lifted. At the same time, when the pilot pressure is applied to the first pilot relief valve 412 in the intersecting pilot oil circuit, the first pilot relief valve 412 opens to realize reverse flow and returns to the oil tank. With such an arrangement, the high-pressure oil entering the rod chamber is used as the pilot control oil of the first pilot relief valve 412. After the first pilot relief valve 412 is opened, the hydraulic oil can be slowly returned by adjusting the pilot pressure, so as to prevent the bulldozer cylinder 3 from falling suddenly.

[0122] When the bulldozer is lowered and moves in a straight line:

[0123] Different from the single action of lowering the bulldozer blade, when the two compound actions are performed simultaneously, the controller controls the main pump 1 to supply oil to the first oil supply port P1 and the second oil supply port P2 at the same time. The oil circuit corresponding to the first oil supply port P1 supplies the bulldozer blade lowering action. Specifically, the pilot control handle 5 is pushed forward, and the first pilot oil port of the bulldozer valve 21 moves its valve core to the right (to the lowering working position) under the pressure of the pilot control oil; at the same time, the pilot control oil flows through the shuttle valve 27 and the first check valve 29 in turn to push the valve core of the linear travel valve 22 to move to the right (to the first working position); at this time, the valve core XBp1 of the first mid-position cut-off valve 25 connected to the pilot oil port PTa moves to the left (to the cut-off working position), and the valve core XBp2 of the second mid-position cut-off valve 26 moves to the right (to the cut-off working position), realizing mid-position cut-off;

[0124] The oil circuit corresponding to the second oil supply port P2 supplies the travel motors on both sides. When moving forward at the same time, the second pilot oil port XBtr of the right travel valve 24 moves its valve core to the left (to put it in the second working position) under the pressure of the pilot control oil, and the second oil supply port P2 is connected with the pilot oil port Btr; at the same time, the first pilot oil port XBtl of the left travel valve 23 moves its valve core to the right (to put it in the first working position) under the pressure of the pilot control oil; the second oil supply port P2 is connected with the pilot oil port BtL; when the bulldozer is lowered under the action of the linear travel valve 22, the travel will not deviate; when the bulldozer is lowered and the travel is backward at the same time, the same is true, and no further explanation is given;

[0125] The main pump 1 passes the high-pressure oil into the sixth oil port of the right travel valve 24 through the second oil supply port P2, and then into the working oil port of the right travel motor through its second oil port; at the same time, the main pump 1 passes the high-pressure oil into the third oil port of the linear travel valve 22 through the second oil supply port P2, and then into the seventh oil port of the left travel valve 23 through its second oil port, and then into the working oil port of the left travel motor through its fourth oil port;

[0126] The main pump 1 passes the high-pressure oil through the first oil supply port P1 into the fourth oil port of the linear travel valve 22, and then into the fourth oil port of the bulldozer valve 21 through its first oil port, and flows out from the first oil port of the bulldozer valve 21 into the first one-way balance valve 41 of the two-way balance valve 4, and then enters the rodless chamber of the bulldozer cylinder 3 to lower the bulldozer blade. At the same time, the overflow valve of the second one-way balance valve 42, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank;

[0127] Specifically, the high-pressure oil flows into the first oil port of the two-way balance valve 4, passes through the fourth one-way valve 411, and flows into the rodless chamber of the bulldozer cylinder 3 via the third oil port of the two-way balance valve 4, so as to maintain the load and prevent reverse movement. The piston rod of the bulldozer cylinder 3 pushes the bulldozer blade downward, and at the same time, when the pilot pressure is applied to the second pilot relief valve 422 in the intersecting pilot oil circuit, the second pilot relief valve 422 opens to realize reverse flow and returns to the oil tank; in such a configuration, the high-pressure oil entering the rodless chamber is used as the pilot control oil of the second pilot relief valve 422. After the second pilot relief valve 422 is opened, the hydraulic oil can be slowly returned by adjusting the pilot pressure, so as to prevent the bulldozer cylinder 3 from falling suddenly;

[0128] When the bulldozer is lifted and moves in a straight line:

[0129] Different from the single action of lowering the bulldozer blade, when the two compound actions are performed simultaneously, the controller controls the main pump 1 to supply oil to the first oil supply port P1 and the second oil supply port P2 at the same time. The oil circuit corresponding to the first oil supply port P1 supplies the bulldozer blade lifting action. Specifically, the pilot control handle 5 is pushed to move backward, and the valve core of the second pilot oil port of the bulldozer valve 21 moves to the left (to put it in the lifting working position) under the pressure of the pilot control oil; at the same time, the pilot control oil flows through the shuttle valve 27 and the first check valve 29 in turn to push the valve core of the linear travel valve 22 to move to the right (to put it in the first working position); at this time, the valve core XBp1 of the first mid-position cut-off valve 25 connected to the pilot oil port PTa moves to the left (to put it in the cut-off working position), and the valve core XBp2 of the second mid-position cut-off valve 26 moves to the right (to put it in the cut-off working position), realizing the mid-position cut-off;

[0130] The oil circuit corresponding to the second oil supply port P2 supplies the travel motors on both sides. When moving forward at the same time, the second pilot oil port XBtr of the right travel valve 24 moves its valve core to the left (to be in the second working position) under the pressure of the pilot control oil, and the second oil supply port P2 is connected with the pilot oil port Btr; at the same time, the first pilot oil port XBtl of the left travel valve 23 moves its valve core to the right (to be in the first working position) under the pressure of the pilot control oil; the second oil supply port P2 is connected with the pilot oil port BtL; when the bulldozer is lowered under the action of the linear travel valve 22, the travel will not deviate; when the bulldozer is lifted and moving backward at the same time, the same is true, and no further explanation is given;

[0131] The main pump 1 passes the high-pressure oil into the sixth oil port of the right travel valve 24 through the second oil supply port P2, and then into the working oil port of the right travel motor through its second oil port; at the same time, the main pump 1 passes the high-pressure oil into the third oil port of the linear travel valve 22 through the second oil supply port P2, and then into the seventh oil port of the left travel valve 23 through its second oil port, and then into the working oil port of the left travel motor through its fourth oil port;

[0132] The main pump 1 passes the high-pressure oil through the first oil supply port P1 into the fourth oil port of the linear travel valve 22, and then into the fourth oil port of the bulldozer valve 21 through its first oil port, and flows out from the second oil port of the bulldozer valve 21 into the second one-way balance valve 42 of the two-way balance valve 4, and then into the rod chamber of the bulldozer cylinder 3 to lift the bulldozer blade. At the same time, the overflow valve of the first one-way balance valve 41, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank;

[0133] Specifically, the high-pressure oil flows into the second oil port of the two-way balance valve 4, passes through the fifth one-way valve 421, and flows into the rod chamber of the bulldozer cylinder 3 via the fourth oil port of the two-way balance valve 4, so as to maintain the load and prevent reverse movement. The piston rod of the bulldozer cylinder 3 retracts and the bulldozer is lifted. At the same time, when the pilot pressure is applied to the first pilot relief valve 412 in the intersecting pilot oil circuit, the first pilot relief valve 412 opens to realize reverse flow and returns to the oil tank. With such an arrangement, the high-pressure oil entering the rod chamber is used as the pilot control oil of the first pilot relief valve 412. After the first pilot relief valve 412 is opened, the hydraulic oil can be slowly returned by adjusting the pilot pressure, so as to prevent the bulldozer cylinder 3 from falling suddenly.

[0134] In the present invention, during the lowering and lifting of the bulldozer blade, the bulldozer blade can be prevented from falling suddenly during operation by controlling the first one-way balancing valve 41 and the second one-way balancing valve 42 which are mutually pilot controlled in the two-way balance.

[0135] By adding a first one-way valve 29 flowing into the pilot oil port PTa of the linear travel valve 22 and cooperating with the shuttle valve 27, it can also simultaneously meet one or any two of the four actions of the boom, arm, bucket, rotation, or a combined action. When operating the travel action at the same time, it can ensure that the pilot pressure can push the valve core of the linear travel valve 22 to ensure that the excavator travels in a straight line without deviation.

[0136] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A hydraulic system for an excavator bulldozer, characterized in that: include: A main pump, a main valve group connected to the main pump, a bulldozer cylinder connected to the main valve group, and a two-way balancing valve arranged between the main valve group and the bulldozer cylinder; The main valve group includes a bulldozer valve, a linear travel valve, a left travel valve, a right travel valve, and a first mid-position cut-off valve and a second mid-position cut-off valve; the main valve group is provided with a first oil supply port and a second oil supply port connected to the main pump, and the two-way balancing valve includes a first one-way balancing valve and a second one-way balancing valve which are mutually pilot-controlled; The second oil supply port is connected to the oil port of the right travel valve and is also connected to the oil port of the linear travel valve; the first oil supply port is connected to the oil port of the linear travel valve; The oil port of the linear travel valve is connected to the oil port of the left travel valve; The oil port of the linear travel valve is connected to the oil port of the bulldozer valve and is also connected to the oil port of the second mid-position cut-off valve; The first oil port and the second oil port of the right travel valve are respectively used to connect with the two working oil ports of the right travel motor, the oil port of the right travel valve is connected with the oil port of the second middle position cut-off valve, and the oil port of the second middle position cut-off valve is connected with the oil port of the bulldozer valve. The third oil port and the fourth oil port of the left travel valve are respectively used to connect with the two working oil ports of the left travel motor, the oil port of the left travel valve is connected with the oil port of the first middle position cut-off valve, and the oil port of the first middle position cut-off valve is connected with the oil port of the bulldozer valve. The first oil port of the bulldozer valve is connected to the conducting end of the first one-way balancing valve, and the conducting end away from the conducting end of the first one-way balancing valve is connected to the rodless chamber of the bulldozer cylinder; the second oil port of the bulldozer valve is connected to the conducting end of the second one-way balancing valve, and the conducting end away from the conducting end of the second one-way balancing valve is connected to the rod chamber of the bulldozer cylinder.

2. The hydraulic system of an excavator bulldozer according to claim 1, characterized in that: The hydraulic system also includes a pilot control handle, a shuttle valve is also provided in the main valve group, and a plurality of pilot oil ports are also provided on the valve block of the main valve group; The bulldozer valve, the linear travel valve, the left travel valve, the right travel valve, the first center cut-off valve and the second center cut-off valve are all pilot hydraulically controlled valves; The pilot control handle has a first pilot oil port and a second pilot oil port, the first pilot oil port is connected to the first pilot oil port of the bulldozer valve and is also connected to the first oil port of the shuttle valve; The second pilot oil port is connected to the second pilot oil port of the bulldozer valve and is also connected to the second oil port of the shuttle valve; The third oil port of the shuttle valve is connected to the pilot oil ports of the first center cut-off valve and the second center cut-off valve respectively, and is also connected to the pilot oil port of the linear travel valve through the first non-return valve; The first pilot oil port and the second pilot oil port of the left travel valve are respectively connected to the pilot oil port on the valve block; The first pilot oil port and the second pilot oil port of the right travel valve are respectively connected to the pilot oil ports on the valve block.

3. The hydraulic system of an excavator bulldozer according to claim 2, characterized in that: The fifth oil port of the right travel valve is connected to the oil return circuit, and the fourth oil port and the eighth oil port thereof are respectively connected to the pilot oil port on the valve block; The eighth oil port of the left travel valve is connected to the oil return circuit, and the fifth oil port and the first oil port of the left travel valve are respectively connected to the pilot oil port on the valve block.

4. The hydraulic system of an excavator bulldozer according to any one of claims 1 to 3, characterized in that: The main valve assembly further includes a main overflow valve, the first oil supply port is connected to the main overflow valve via a second one-way valve, and the second oil supply port is connected to the main overflow valve via a third one-way valve.

5. The hydraulic system of an excavator bulldozer according to any one of claims 1 to 3, characterized in that: The bulldozer valve is a mid-position three-position four-way valve; The linear travel valve is a two-position four-way valve; The left travel valve and the right travel valve are both mid-position three-position eight-way valves; The first center cut-off valve and the second center cut-off valve are both two-position two-way valves.

6. The hydraulic system of an excavator bulldozer according to any one of claims 1 to 3, characterized in that: The first one-way balancing valve includes a fourth one-way valve and a first pilot relief valve connected in parallel; the second one-way balancing valve includes a fifth one-way valve and a second pilot relief valve connected in parallel, and the first pilot relief valve and the second pilot relief valve are mutually staggered pilot control connected.

7. The hydraulic system of an excavator bulldozer according to any one of claims 1 to 3, characterized in that: A multi-connected three-way valve is also arranged between the pilot control handle and the main valve group. The multi-connected three-way valve is provided with a first pressure sensor and a second pressure sensor, which are respectively used to monitor the pilot pressure so as to control the oil supply channel of the main pump through the first oil supply port and / or the second oil supply port.

8. A method for controlling a hydraulic system of an excavator bulldozer according to any one of claims 1 to 7, characterized in that: The steps include: When the bulldozer is lowered: The main pump makes the high-pressure oil flow through the second oil supply port, through the right travel valve in sequence, and then enters the fourth oil port of the bulldozer valve, and flows out from the first oil port of the bulldozer valve and enters the first one-way balance valve of the two-way balance valve, and then enters the rodless chamber of the bulldozer cylinder to lower the bulldozer blade, and at the same time, the overflow valve of the second one-way balance valve, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank; When the bulldozer is raised: The main pump makes the high-pressure oil flow through the second oil supply port, through the right travel valve, and then into the fourth oil port of the bulldozer valve, and then flows out from the second oil port of the bulldozer valve and enters the second one-way balance valve of the two-way balance valve, and then enters the rod chamber of the bulldozer cylinder to lift the bulldozer blade, and at the same time, the overflow valve of the first one-way balance valve, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank; When the bulldozer is lowered and moves in a straight line: The main pump supplies high-pressure oil to the sixth oil port of the right travel valve through the second oil supply port, and then to the working oil port of the right travel motor through its second oil port; at the same time, the main pump supplies high-pressure oil to the third oil port of the linear travel valve through the second oil supply port, and then to the seventh oil port of the left travel valve through its second oil port, and then to the working oil port of the left travel motor through its fourth oil port; The main pump passes the high-pressure oil through the first oil supply port into the fourth oil port of the linear travel valve, and then into the fourth oil port of the bulldozer valve through its first oil port, and flows out from the first oil port of the bulldozer valve into the first one-way balancing valve of the two-way balancing valve, and then into the rodless chamber of the bulldozer cylinder to lower the bulldozer blade, and at the same time, the overflow valve of the second one-way balancing valve, which is mutually pilot-controlled, opens to flow in the reverse direction and then returns to the oil tank; When the bulldozer is lifted and moves in a straight line: The main pump supplies high-pressure oil to the sixth oil port of the right travel valve through the second oil supply port, and then to the working oil port of the right travel motor through its second oil port; at the same time, the main pump supplies high-pressure oil to the third oil port of the linear travel valve through the second oil supply port, and then to the seventh oil port of the left travel valve through its second oil port, and then to the working oil port of the left travel motor through its fourth oil port; The main pump sends high-pressure oil into the fourth oil port of the linear travel valve through the first oil supply port, and then into the fourth oil port of the bulldozer valve through its first oil port. After flowing out from the second oil port of the bulldozer valve, it enters the second one-way balancing valve of the two-way balancing valve, and then enters the rod chamber of the bulldozer cylinder to lift the bulldozer. At the same time, the overflow valve of the first one-way balancing valve, which is pilot-controlled to each other, opens to flow in the reverse direction and returns to the oil tank.

9. The control method of the hydraulic system of an excavator bulldozer according to claim 8, characterized in that: Before the main pump supplies oil, the valve core of each valve moves to the corresponding working position under the action of the pilot control oil; When the bulldozer is lowered: Under the pressure of the pilot control oil, the valve core of the first pilot oil port of the bulldozer valve moves to the right; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off; When the bulldozer is raised: Under the pressure of the pilot control oil, the valve core of the second pilot oil port of the bulldozer valve moves to the left; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off; When the bulldozer is lowered and moves in a straight line: Under the pressure of the pilot control oil, the valve core of the first pilot oil port of the bulldozer valve moves to the right; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off; The valve core of the second pilot oil port of the right travel valve moves to the left under the pressure of the pilot control oil, and the valve core of the first pilot oil port of the left travel valve moves to the right under the pressure of the pilot control oil; When the bulldozer is lifted and moves in a straight line: Under the pressure of the pilot control oil, the valve core of the second pilot oil port of the bulldozer valve moves to the left; at the same time, the pilot control oil flows through the shuttle valve and the first check valve in sequence to push the valve core of the linear travel valve to move to the right; the valve core of the first mid-position cut-off valve moves to the left, and the valve core of the second mid-position cut-off valve moves to the right, realizing mid-position cut-off; The valve core of the second pilot oil port of the right travel valve moves to the left under the pressure of the pilot control oil, and the valve core of the first pilot oil port of the left travel valve moves to the right under the pressure of the pilot control oil.

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