Hydraulic lifting system and tractor

Abstract

The invention provides a hydraulic lifting system and a tractor. Comprising an oil tank, a main oil supply way, a main oil return way, a lifting cylinder, a first reversing valve, a switching valve and an oil supplementing way. By arranging the oil supplementing oil way, when vacuum negative pressure is formed in the rod cavity of the lifting cylinder, hydraulic oil in the main oil return oil way can flow back to the rod cavity of the lifting cylinder, oil supplementing of the rod cavity of the lifting cylinder is achieved, it is guaranteed that the pressure in the whole hydraulic system is stable, and hydraulic elements are prevented from being damaged. Moreover, the high-pressure function and the non-high-pressure function are switched through the switching valve, the first reversing valve and the switching valve can be separately arranged, the arrangement of the whole scheme is not limited by the space of the whole machine, and the hydraulic system has the advantages of being easy to maintain, convenient to replace parts and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of tractors, in particular to a hydraulic lifting system and a tractor. Background Art

[0002] In the prior art, when the lifting cylinder of a tractor uses a high-pressure hydraulic lifting system and the lowering speed of the lifting cylinder is too high under the action of a load, a vacuum negative pressure will be formed in the rod chamber of the lifting cylinder, causing the hydraulic oil in the hydraulic lifting system to be forced to flow back to the rod chamber of the lifting cylinder, thereby affecting the stability and safety of the hydraulic lifting system. Therefore, it is necessary to provide a hydraulic lifting system and a tractor to overcome the above-mentioned defects. Summary of the invention

[0003] The object of the present invention is to provide a hydraulic lifting system and a tractor.

[0004] According to one aspect of the present invention, a hydraulic lifting system and a tractor are provided, comprising: a fuel tank; a main oil supply oil circuit, the main oil supply oil circuit is connected in series with an oil pump and is connected to the fuel tank through the oil pump, and can provide pressurized hydraulic oil; a main oil return oil circuit, the main oil return oil circuit is connected to the fuel tank; a lifting cylinder, the lifting cylinder includes a rod chamber and a rodless chamber; a first reversing valve, the first reversing valve includes a first oil inlet, a first oil return port, a first working oil port and a second working oil port, the first oil inlet is connected to the main oil supply oil circuit, the first oil return port is connected to the main oil return oil circuit, the first working oil port is The rodless chamber is connected, and the second working oil port is connected to the rod chamber; a switching valve, the switching valve includes a third oil inlet connected to the first working oil port, a third oil return port connected to the main return oil circuit and / or the oil tank, and a fifth working oil port connected to the rodless chamber; under the high-pressure working state, the third oil inlet is connected to the fifth working oil port; under the non-high-pressure working state, the third oil return port is connected to the fifth working oil port; an oil replenishment circuit, an oil replenishment valve is arranged on the oil replenishment circuit, and the oil replenishment valve can reflux the main return oil circuit to the third oil inlet in one direction.

[0005] Preferably, a back pressure valve is also connected in series to the main oil return line.

[0006] Preferably, the switching valve also includes a sixth working oil port connected to the oil tank, and the third oil return port is connected to the oil inlet of the oil replenishing valve; in the high-pressure working state, the third oil return port is connected to the sixth working oil port; in the non-high-pressure working state, the third oil inlet port is connected to the sixth working oil port.

[0007] Preferably, it also includes a second reversing valve, which includes a second oil inlet, a second oil return port, a third working oil port and a fourth working oil port, the second oil inlet is connected to the main oil supply circuit, the second oil return port is connected to the main oil return circuit, and the third working oil port and the fourth working oil port are connected to the hydraulic output connector.

[0008] Preferably, the oil pump is a load-sensitive plunger pump.

[0009] Preferably, an oil pressure compensation valve is provided between the first oil inlet and / or the second oil inlet and the main oil supply circuit.

[0010] Preferably, it also includes: a first shuttle valve, an oil inlet of the first shuttle valve is connected to the first oil inlet, and another oil inlet of the first shuttle valve is connected to the third oil inlet; a second shuttle valve, an oil inlet of the second shuttle valve is connected to the oil outlet of the first shuttle valve, another oil outlet of the second shuttle valve is connected to the second oil inlet, and the oil outlet of the second shuttle valve is connected to an oil inlet of the next second shuttle valve or a sensor end of a load-sensitive plunger pump.

[0011] Preferably, a throttle valve is connected in series between one oil inlet of the first shuttle valve and the first oil inlet, between another oil inlet of the first shuttle valve and the third oil inlet, and between another oil outlet of the second shuttle valve and the second oil inlet.

[0012] Preferably, a first safety valve is further provided between the main oil supply circuit and the main oil return circuit; and an oil filter device is connected in series to the main oil supply circuit and / or the main oil return circuit.

[0013] According to another aspect of the present invention, a tractor is provided, comprising the hydraulic lifting system.

[0014] Compared with the prior art, the hydraulic lifting system and tractor provided by the present invention have the following beneficial effects:

[0015] The present invention provides an oil replenishment circuit. When a vacuum negative pressure is formed in the rod chamber of the lifting cylinder, the hydraulic oil in the main oil return circuit can flow back to the rod chamber of the lifting cylinder, thereby replenishing the rod chamber of the lifting cylinder, ensuring the pressure stability in the entire hydraulic system and avoiding damage to the hydraulic components.

[0016] Moreover, the present invention realizes the conversion between high pressure and non-high pressure functions through a switching valve, the load-sensitive multi-way valve and the high pressure-non-high pressure switching valve can be arranged separately, the layout of the entire solution is not limited by the space of the whole machine, and the hydraulic system has the characteristics of simple maintenance and convenient replacement of parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0018] Figure 1 This is a structural schematic diagram of a hydraulic lifting system in Example 1 of the present invention;

[0019] Figure 2 This is a structural schematic diagram of another hydraulic lifting system in Example 1 of the present invention;

[0020] Figure 3 Schematic diagram of the structure of the first reversing valve in Example 1 of the present invention;

[0021] Figure 4 Schematic diagram of the structure of the second reversing valve in Example 1 of the present invention;

[0022] Figure 5 This is a schematic diagram of the structure and connection of the switching valve in Example 1 of the present invention;

[0023] Figure 6 It is a structural schematic diagram of the hydraulic lifting system in Example 2 of the present invention;

[0024] Figure 7 Schematic diagram of the structure of the first reversing valve in Embodiment 2 of the present invention;

[0025] Figure 8 Schematic diagram of the structure of the second reversing valve in Embodiment 2 of the present invention;

[0026] Fig. 9 Schematic diagram of the structure and connection of the switching valve in Example 2 of the present invention.

[0027] Description of reference numerals: 1, oil tank; 2, oil pump; 3, lifting cylinder; 31, rod chamber; 32, rodless chamber; 4, multi-way valve; 41, first reversing valve; P1, first oil inlet; T1, first oil return port; A1, first working oil port; B1, second working oil port; 42, second reversing valve; P2, second oil inlet; T2, second oil return port;

[0028] A2, third working oil port; B2, fourth working oil port; 43, overflow safety valve; 44, oil pressure compensation valve; 45, first shuttle valve; 46, second shuttle valve; 51, switching valve; P3, third oil inlet; T3, third oil return port; A3, fifth working oil port; 52, oil replenishment valve; 53, throttle valve; 6, back pressure valve; 7, hydraulic output connector; 81, oil suction filter; 82, pressure filter; 83, return filter;

[0029] L1, main oil supply circuit; L2, main oil return circuit; L3, oil replenishment circuit; L4, feedback circuit. DETAILED DESCRIPTION

[0030] 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 these drawings without paying creative work.

[0031] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0032] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0033] In this document, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In addition, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0036] Example 1

[0037] See also Figures 1 to 5 The present embodiment provides a hydraulic lifting system for a tractor, the hydraulic lifting system comprising: an oil tank 1, a main oil supply circuit L1, a main oil return circuit L2, a lifting cylinder 3, a multi-way valve 4, a switching valve 51 and an oil replenishment circuit L3.

[0038] See attached Figures 1 to 3The main oil supply circuit L1 is connected in series with an oil pump 2, which is connected to the oil tank 1 through the oil pump to provide pressurized hydraulic oil for the hydraulic system. The oil pump 2 can be, but is not limited to, a vane pump, a gear pump, a plunger pump or a threaded pump. The main oil return circuit L2 is connected to the oil tank 1 to guide the hydraulic oil back to the oil tank 1. The lifting cylinder 3 includes a rod chamber 31 and a rodless chamber 32. The piston rod in the rod chamber 31 is connected to the lifter to achieve lifting and lowering of the load.

[0039] The first reversing valve 41 includes a first oil inlet P1, a first oil return port T1, a first working oil port A1 and a second working oil port B1. The first oil inlet P1 is connected to the main oil supply oil circuit L1, the first oil return port T1 is connected to the main oil return oil circuit L2, the first working oil port A1 is connected to the rodless chamber 32, and the second working oil port B1 is connected to the rod chamber 31. The first reversing valve 41 includes a first state and a second state. In the first state, the first oil inlet P1 is connected to the first working oil port A1, and the first oil return port T1 is connected to the second working oil port B1, so as to realize the lifting of the lifting cylinder 3. In the second state, the first oil inlet P1 is connected to the second working oil port B1, and the first oil return port T1 is connected to the first working oil port A1, so as to realize the lowering of the lifting cylinder 3. Of course, for the technology in the field, the first reversing valve 41 can also include a neutral state and a unloading state.

[0040] See attached Figure 1 , 2 , 5, the switching valve 51 includes a third oil inlet P3 connected to the first working oil port A1, a third oil return port T3 connected to the main oil return oil circuit L2 and / or the oil tank 1, and a fifth working oil port A3 connected to the rodless chamber 32. In the strong pressure working state, the third oil inlet P3 is connected to the fifth working oil port A3; in the non-strong pressure working state, the third oil return port T3 is connected to the fifth working oil port A3.

[0041] An oil replenishment valve 52 is provided on the oil replenishment circuit L3. Preferably, the oil replenishment valve 52 is a first one-way valve, the oil inlet end of the first one-way valve is connected to the main oil return circuit L2, and the oil outlet end of the first one-way valve is connected to the third oil inlet P3, which can unidirectionally return the hydraulic oil in the main oil return circuit L2 and / or the oil tank 1 to the third oil inlet P3. In other words, the third oil inlet P3 can be connected to the oil tank 1, or to the main oil return circuit L2, or to both the oil tank 1 and the main oil return circuit L2. It can be understood that the above three methods can all achieve the oil replenishment function.

[0042] In this embodiment, the third oil inlet P3 is connected to both the oil tank 1 and the main oil return line L2. Specifically, the switching valve 51 also includes a sixth working oil port B3 connected to the oil tank 1, and the third oil return port T3 is connected to the oil inlet of the oil replenishment valve 52. Under the strong pressure working state, the third oil return port T3 is connected to the sixth working oil port B3. That is to say, under the strong pressure working state, the oil replenishment valve 52 is connected to the main oil return line L2 on the one hand, and is connected to the oil tank 1 through the third oil return port T3 and the sixth working oil port B3 on the other hand, so that the main oil return line L2 and the hydraulic oil of the oil tank 1 can be unidirectionally returned to the third oil inlet P3, thereby achieving a better oil replenishment effect.

[0043] In order to further improve the oil replenishment effect of the entire system, a back pressure valve 6 is further arranged on the main oil return circuit L2. The back pressure valve 6 is preferably a second one-way valve. The inlet side of the second one-way valve is connected to the oil tank 1, thereby increasing the valve resistance of the main oil return circuit L2 close to the oil tank 1, and preventing the hydraulic oil of the first oil return port T1 from directly flowing back to the oil tank 1 during the oil replenishment process, so that the hydraulic oil of the first oil return port T1 is preferentially returned to the oil replenishment circuit L3, thereby improving the oil replenishment effect on the rod chamber 31 of the lifting cylinder 3.

[0044] The switching valve 51 is an electromagnetic reversing valve, and the electromagnetic reversing valve is controlled by an electric control switch to switch between the strong pressure and non-strong pressure working states of the lifting cylinder 3. The first reversing valve 41 is controlled by a joystick to switch between the lifting and lowering working states of the lifting cylinder 3.

[0045] Under the strong pressure working state, the switching valve 51 is in the right position, the third oil inlet P3 is connected to the fifth working oil port A3, the third oil return port T3 is in the cut-off state, the rodless chamber 32 of the lifting cylinder 3 is connected to the first working oil port A1 of the first reversing valve 41, and the rod chamber 31 of the lifting cylinder 3 is connected to the second working oil port B1 of the first reversing valve 41. The lifting cylinder 3 is a double-acting lifting cylinder 3, and the lifting cylinder 3 is switched between the cylinder lifting and lowering states under the control of the first reversing valve 41.

[0046] The oil inlet path of the hydraulic oil circuit under the strong pressure lifting condition is: oil tank 1→oil pump 2→main oil supply circuit L1→first oil inlet port P1 of first reversing valve 41→first working oil port A1 of first reversing valve 41→rodless chamber 32 of lifting cylinder 3. The oil return route of the hydraulic oil circuit under the strong pressure lifting condition is: rod chamber 31 of lifting cylinder 3→fifth working oil port A3 of switching valve 51→third oil inlet port P3 of switching valve 51→second working oil port B1 of first reversing valve 41→first oil return port T1 of first reversing valve 41→main oil return circuit L2→oil tank 1.

[0047] The oil inlet path of the hydraulic oil circuit under the strong pressure lowering condition is: oil tank 1→oil pump 2→main oil supply circuit L1→first oil inlet port P1 of first reversing valve 41→second working oil port B1 of reversing valve→third oil inlet port P3 of switching valve 51→fifth working oil port A3 of switching valve 51→rod chamber 31 of lifting cylinder 3. The oil return path of the hydraulic oil circuit under the strong pressure lowering condition is:rodless chamber 32 of lifting cylinder 3→first working oil port A1 of first reversing valve 41→first oil return port T1 of first reversing valve 41→main oil return circuit L2→oil tank 1.

[0048] In the strong pressure descending state, when the load is too large, the lifting cylinder 3 descends rapidly, and the actual descending speed of the lifting cylinder 3 will be greater than the descending speed provided by the hydraulic lifting system. The rod chamber 31 of the lifting cylinder 3 will form a vacuum negative pressure, and the hydraulic oil in the main return oil circuit L2 will partially flow back to the rod chamber 32 of the lifting cylinder 3, thereby replenishing the rod chamber 31 of the lifting cylinder 3, reducing the impact on the oil circuit on the side of the first reversing valve 41, ensuring the pressure stability in the entire hydraulic system, and avoiding damage to the hydraulic components.

[0049] The hydraulic oil circuit oil replenishment path under the strong pressure descending condition is: the rodless chamber 32 of the lifting cylinder 3 → the first working oil port A1 of the first reversing valve 41 → the first oil return port T1 of the first reversing valve 41 → the main oil return oil circuit L2 → the oil replenishment valve 52 → the third oil inlet P3 of the switching valve 51 → the fifth working oil port A3 of the switching valve 51 → the rod chamber 31 of the lifting cylinder 3; and / or, the oil tank 1 → the sixth working oil port B3 of the switching valve 51 → the third oil return port T3 of the switching valve 51 → the oil replenishment valve 52 → the third oil inlet P3 of the switching valve 51 → the fifth working oil port A3 of the switching valve 51 → the rod chamber 31 of the lifting cylinder 3.

[0050] The oil inlet path of the hydraulic oil circuit under non-high-pressure lifting conditions is: oil tank 1→oil pump 2→main oil supply circuit L1→first oil inlet port P1 of first reversing valve 41→first working oil port A1 of first reversing valve 41→rodless chamber 32 of lifting cylinder 3; the oil return route of the hydraulic oil circuit under non-high-pressure lifting conditions is: rod chamber 31 of lifting cylinder 3→fifth working oil port A3 of switching valve 51→third oil return port T3 of switching valve 51→main oil return circuit L2→oil tank 1.

[0051] In the non-strong pressure state, the lifting cylinder 3 naturally descends under the load until the load is balanced. The return and inlet paths of the hydraulic oil circuit under the non-strong pressure descending condition are: the rodless chamber 32 of the lifting cylinder 3 → the first working oil port A1 of the first reversing valve 41 → the first return oil port T1 of the first reversing valve 41 → the main return oil circuit L2 → the third return oil port T3 of the switching valve 51 → the fifth working oil port A3 of the switching valve 51 → the rod chamber 31 of the lifting cylinder 3.

[0052] See attached Figure 4The second reversing valve 42 includes a second oil inlet P2, a second oil return port T2, a third working oil port A2 and a fourth working oil port B2. The second oil inlet P2 is connected to the main oil supply oil circuit L1, the second oil return port T2 is connected to the main oil return oil circuit L2, and the third working oil port A2 and the fourth working oil port B2 are connected to the hydraulic output connector 7. The hydraulic output connector 7 is connected to the attached agricultural implement to realize the control of the attached agricultural implement. The implementation method is similar to the principle of the first reversing valve 41, which will not be repeated here. The number of the second reversing valves 42 is selected according to actual needs, preferably 2 to 6 groups.

[0053] In addition, an overflow safety valve 43 is provided between the main oil supply line L1 and the main oil return line L2 to ensure that the working pressure of the hydraulic system does not exceed the specified value; an oil filter device is connected in series to the main oil supply line L1, see the attached Figure 1 , 2 The oil filtering device includes an oil suction filter 81 located at the oil inlet side of the oil pump 2 and a pressure filter 82 arranged at the oil outlet side of the oil pump 2.

[0054] Example 2

[0055] In this embodiment, the structure of the oil pump 2 and the multi-way valve 4 (i.e., the first reversing valve 41 and the second reversing valve 42 in the embodiment 1) are improved on the basis of the embodiment 1. It should be noted that the structure and connection method of the hydraulic components not specifically described in this embodiment are the same as those in the embodiment 1.

[0056] See attached Figures 6 to 9 In this embodiment, the oil pump 2 is a load-sensitive plunger pump. Correspondingly, the multi-way valve 4 in this embodiment adopts a load-sensitive valve with a load feedback function. The load-sensitive plunger pump is equipped with a sensor that can monitor the feedback pressure of the hydraulic lifting system and adjust the oil flow pressure according to the feedback pressure of the load-sensitive valve to meet the pressure requirements of the entire hydraulic lifting system. A pressure feedback oil circuit L4 is provided in the hydraulic lifting system to obtain the maximum pressure of the entire hydraulic lifting system.

[0057] See attached Figure 7, the first reversing valve 41 includes a first oil inlet P1, a first oil return port T1, a first working oil port A1, and a second working oil port B1. The first oil inlet P1 is connected to the main oil supply circuit L1, the first oil return port T1 is connected to the main oil return circuit L2, the first working oil port A1 is connected to the rodless chamber 32, and the second working oil port B1 is connected to the rod chamber 31. The first reversing valve 41 includes a first state and a second state. In the first state, the first oil inlet P1 is connected to the first working oil port A1, and the first oil return port T1 is connected to the second working oil port B1, so as to realize the lifting of the lifting cylinder 3. In the second state, the first oil inlet P1 is connected to the second working oil port B1, and the first oil return port T1 is connected to the first working oil port A1, so as to realize the lowering of the lifting cylinder 3. The second reversing valve 42 in this embodiment has the same structure as the first reversing valve 41. For the specific structure, please refer to the attached. Figure 8 , I will not go into details here.

[0058] In order to ensure the oil pressure stability of the first reversing valve 41 and the second reversing valve 42, an oil pressure compensation valve 44 is provided between the first oil inlet P1 and / or the second oil inlet P2 and the main oil supply oil circuit L1. In this embodiment, the oil pressure compensation valve 44 is a pre-valve compensation, but for those skilled in the art, the oil pressure compensation valve 44 can also be a post-valve compensation.

[0059] See attached Figure 6 The feedback oil circuit L4 includes a first shuttle valve 45 and a second shuttle valve 46. One oil inlet of the first shuttle valve 45 is connected to the first oil inlet P1, and the other oil inlet of the first shuttle valve 45 is connected to the third oil inlet P3. The number of the second shuttle valves 46 is the same as the number of the second reversing valves 42. One oil inlet of the second shuttle valve 46 is connected to the oil outlet of the first shuttle valve 45, and the other oil outlet of the second shuttle valve 46 is connected to the second oil inlet P2. The oil outlet of the second shuttle valve 46 is connected to one oil inlet of the next second shuttle valve 46, until the oil outlet of the last second shuttle valve 46 is connected to the sensor end of the load-sensitive plunger pump, so as to transmit the pressure of the hydraulic oil circuit of the multi-way valve 4 to the sensitive plunger pump. A throttle valve 53 is connected in series between one oil inlet of the first shuttle valve 45 and the first oil inlet P1, between the other oil inlet of the first shuttle valve 45 and the third oil inlet P3, and between the other oil outlet of the second shuttle valve 46 and the second oil inlet P2.

[0060] It should be noted that in order to simplify the connection line of the switching valve 51, refer to the attached Figure 6 , 9 In this embodiment, the sixth working oil port B3 is in a cut-off state, the third oil return port T3 is connected to the oil replenishment circuit L3, and the third oil return port T3 is connected to the oil inlet of the oil replenishment valve 52, and the oil replenishment function is realized through the main oil return circuit L2.

[0061] However, for those skilled in the art, the switching valve 51 in this embodiment may also adopt the same connection method as that in Example 1, that is, the sixth working oil port B3 is directly connected to the oil tank 1, and the third oil return port T3 is connected to the oil inlet of the oil replenishment valve 52. Under the strong pressure working state, the third oil return port T3 is connected to the sixth working oil port B3, and the main return oil circuit L2 and the hydraulic oil of the oil tank 1 are unidirectionally returned to the third oil inlet P3, so as to achieve a better oil replenishment effect.

[0062] In addition, an overflow safety valve 43 is provided between the main oil supply line L1 and the main oil return line L2 to ensure that the working pressure of the hydraulic system does not exceed the specified value. An oil filter device is connected in series to the main oil supply line L1 and / or the main oil return line L2. Figure 6 The oil filter device includes an oil suction filter 81 located at the oil inlet side of the oil pump 2, a pressure filter 82 arranged at the oil outlet side of the oil pump 2, and a return oil filter 83 connected in series to the main return oil circuit L2. The return oil filter 83 can also play a certain back pressure role to prevent the hydraulic oil in the first return oil port T1 from directly flowing back to the oil tank 1 during the oil replenishment process.

[0063] It will be apparent to those skilled in the art that various modifications and variations may be made to the above exemplary embodiments of the present invention without departing from the spirit and scope of the present invention. Therefore, it is intended that the present invention covers modifications and variations of the present invention that fall within the scope of the appended claims and their equivalent technical solutions.

Claims

1. A hydraulic lifting system, characterized in that: include: tank; A main oil supply circuit, wherein the main oil supply circuit is connected in series with an oil pump and is connected to an oil tank through the oil pump, and is capable of providing pressurized hydraulic oil; A main oil return oil circuit, wherein the main oil return oil circuit is connected to the oil tank; A lifting cylinder, the lifting cylinder comprising a rod chamber and a rodless chamber; A first reversing valve, the first reversing valve comprising a first oil inlet, a first oil return port, a first working oil port and a second working oil port, the first oil inlet being connected to a main oil supply oil circuit, the first oil return port being connected to a main oil return oil circuit, the first working oil port being connected to the rodless chamber, and the second working oil port being connected to the rod chamber; A switching valve, the switching valve comprising a third oil inlet connected to the first working oil port, a third oil return port connected to the main oil return oil circuit and / or the oil tank, and a fifth working oil port connected to the rodless chamber; in a high-pressure working state, the third oil inlet is connected to the fifth working oil port; in a non-high-pressure working state, the third oil return port is connected to the fifth working oil port; An oil replenishment circuit is provided with an oil replenishment valve, and the oil replenishment valve can unidirectionally return the hydraulic oil in the main oil return circuit and / or the oil tank to the third oil inlet.

2. The hydraulic lifting system according to claim 1, characterized in that: The main oil return line is also connected in series with a back pressure valve.

3. The hydraulic lifting system according to claim 1, characterized in that: The switching valve further includes a sixth working oil port connected to the oil tank, and the third oil return port is connected to the oil inlet of the oil replenishing valve; in the strong pressure working state, the third oil return port is connected to the sixth working oil port.

4. The hydraulic lifting system according to claim 1, characterized in that: It also includes a second reversing valve, which includes a second oil inlet, a second oil return port, a third working oil port and a fourth working oil port. The second oil inlet is connected to the main oil supply circuit, the second oil return port is connected to the main oil return circuit, and the third working oil port and the fourth working oil port are connected to the hydraulic output connector.

5. The hydraulic lifting system according to claim 4, characterized in that: The oil pump is a load-sensitive plunger pump.

6. The hydraulic lifting system according to claim 5, characterized in that: An oil pressure compensation valve is provided between the first oil inlet and / or the second oil inlet and the main oil supply circuit.

7. The hydraulic lifting system according to claim 6, characterized in that: Also includes: a first shuttle valve, wherein one oil inlet of the first shuttle valve is connected to the first oil inlet, and another oil inlet of the first shuttle valve is connected to the third oil inlet; A second shuttle valve, an oil inlet of the second shuttle valve is connected to the oil outlet of the first shuttle valve, another oil outlet of the second shuttle valve is connected to the second oil inlet, and the oil outlet of the second shuttle valve is connected to an oil inlet of the next second shuttle valve or to the sensor end of the load-sensing plunger pump.

8. The hydraulic lifting system according to claim 7, characterized in that: A throttle valve is connected in series between one oil inlet of the first shuttle valve and the first oil inlet, between another oil inlet of the first shuttle valve and the third oil inlet, and between another oil outlet of the second shuttle valve and the second oil inlet.

9. The hydraulic lifting system according to claim 8, characterized in that: A first safety valve is also provided between the main oil supply circuit and the main oil return circuit; and an oil filter device is connected in series to the main oil supply circuit and / or the main oil return circuit.

10. A tractor, characterized in that: Comprising the hydraulic lifting system as described in any one of claims 1 to 9.

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