Downward pressure control hydraulic system and tractor

Abstract

The invention relates to the technical field of hydraulic control, in particular to a down pressure control hydraulic system and a tractor. The down pressure control hydraulic system comprises a main control valve, a controller, an electromagnetic valve, a first switch valve, a second switch valve, a first one-way valve, a proportional valve and an oil cylinder. The electromagnetic valve is connected with the first one-way valve and the main control valve; the first one-way valve is connected with a first switch valve; the first switch valve is connected with the second switch valve and the main control valve; the second switch valve is communicated with the main control valve; the proportional valve is connected with the main control valve, the first one-way valve and the oil cylinder; the oil cylinder is connected with a first one-way valve; and the controller is in signal connection with the electromagnetic valve, the first switch valve, the second switch valve and the proportional valve. The electromagnetic valve, the proportional valve and the like are connected in series to form an integrated loop, parts and pipelines are reduced, the structure is simplified, and the maintenance difficulty is lowered; electric signals are output through the controller to control all the valves, operators do not need to manually adjust on site, and remote operation is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic control, and in particular to a downforce control hydraulic system and a tractor. Background Art

[0002] With the widespread application of seed drills, the technical platform of seed drills has gradually improved. Not only is there a requirement for precision in seeding, but the auxiliary functions of seeding are also becoming increasingly rich, such as fans, downforce, seeding amount, marking machines, support wheels, side folding, etc.

[0003] The downforce control of existing seed drills mostly relies on mechanical transmission or simple hydraulic circuits, which have obvious defects: the complex structure makes maintenance difficult and requires manual adjustment on site by operators, which is labor-intensive; and the downforce cannot be adjusted in real time according to changes in soil quality, which easily leads to uneven penetration depth of seeding units into the soil, affecting seeding quality. Summary of the Invention

[0004] The object of the present invention is to provide a downforce control hydraulic system and a tractor, which can solve the above-mentioned technical problems.

[0005] In a first aspect, the present invention provides a downforce control hydraulic system, comprising a main control valve, a controller, a solenoid valve, a first switch valve, a second switch valve, a first one-way valve, a proportional valve, and a cylinder; The oil outlet of the main control valve is communicated with the oil inlet of the solenoid valve, and the oil outlet of the solenoid valve is connected to the oil inlet of the first one-way valve and the first oil return port of the main control valve; The oil outlet of the first one-way valve is connected to one end of the first switch valve; The other end of the first switch valve is connected to one end of the second switch valve and the second oil return port of the main control valve; The other end of the second switch valve is connected to the first oil return port of the main control valve; The oil return port of the proportional valve is connected to the second oil return port of the main control valve, and the two inlets and outlets of the proportional valve are connected to the oil outlet of the first one-way valve and the rodless chamber of the oil cylinder respectively; The rod chamber of the oil cylinder is connected to the oil outlet of the first one-way valve; The controller is connected to the solenoid valve, the first switch valve, the second switch valve and the proportional valve by signal, and is used to control the states of the solenoid valve, the first switch valve, the second switch valve and the proportional valve.

[0006] In an optional embodiment, a filter is provided between the oil outlet of the main control valve and the solenoid valve.

[0007] In an optional embodiment, a first flow valve is provided between the oil outlet of the solenoid valve and the first oil return port of the main control valve.

[0008] In an optional embodiment, a second flow valve is provided between the second switch valve and the first oil return port of the main control valve.

[0009] In an optional embodiment, the proportional valve and the oil cylinder constitute a downforce control unit; There are multiple down force control units, and the multiple down force control units are connected in parallel.

[0010] In an optional embodiment, a pressure sensor is provided between the main control valve and the solenoid valve.

[0011] In an optional embodiment, the solenoid valve is configured to allow the pressure oil to pass through in an energized state, block the pressure oil in an unenergized state, and control the switching of the first switch valve and the second switch valve.

[0012] In an optional embodiment, when the system is in a non-operating state, the first switch valve and the second switch valve are passages.

[0013] In an optional embodiment, a second one-way valve is provided on the oil circuit connected to the second oil return port of the main control valve.

[0014] In a second aspect, the present invention provides a tractor comprising the downforce control hydraulic system according to any one of the aforementioned embodiments.

[0015] The beneficial effects of the present invention are: The main control valve is used as the overall oil source control, and solenoid valves, proportional valves, etc. are connected in series to form an integrated circuit, replacing traditional complex mechanical or decentralized hydraulic structures, reducing parts and pipelines, simplifying the structure, and lowering the difficulty of maintenance; the controller outputs electrical signals to control each valve, and operators do not need to manually adjust on site, realizing remote operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without making any creative efforts.

[0017] Figure 1 A schematic diagram of the initial state of the downforce control hydraulic system provided by an embodiment of the present invention; Figure 2 A schematic diagram of a retracted cylinder state of a downforce control hydraulic system provided by an embodiment of the present invention; Figure 3A schematic diagram of the extended state of the oil cylinder of the downforce control hydraulic system provided by an embodiment of the present invention; Figure 4 This is a schematic diagram of the reset state of the downforce control hydraulic system provided by an embodiment of the present invention.

[0018] Icon: 1-main control valve; 2-filter; 3-solenoid valve; 4-first one-way valve; 5-first switch valve; 6-second switch valve; 7-first flow valve; 8-second flow valve; 9-proportional valve; 10-oil cylinder; 11-controller; 12-second one-way valve; 13-pressure sensor. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of 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. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0021] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0022] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like indicate positions or locations based on the positions shown in the accompanying drawings, or the positions or locations in which the inventive product is typically placed when in use. These terms are intended solely to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0024] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0025] The following combination Figure 1-Figure 4 , some embodiments of the present invention are described in detail. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0026] In the first aspect, the present invention provides a downforce control hydraulic system, comprising a main control valve 1, a controller 11, a solenoid valve 3, a first switch valve 5, a second switch valve 6, a first one-way valve 4, a proportional valve 9 and an oil cylinder 10; the oil outlet of the main control valve 1 is connected to the oil inlet of the solenoid valve 3, the oil outlet of the solenoid valve 3 is connected to the oil inlet of the first one-way valve 4 and the first oil return port T0 of the main control valve 1; the oil outlet of the first one-way valve 4 is connected to one end of the first switch valve 5; the other end of the first switch valve 5 is connected to one end of the second switch valve 6 and the second oil return port R0 of the main control valve 1; the The other end of the second switch valve 6 is connected to the first oil return port T0 of the main control valve 1; the oil return port of the proportional valve 9 is connected to the second oil return port R0 of the main control valve 1, and the two inlets and outlets of the proportional valve 9 are respectively connected to the oil outlet of the first one-way valve 4 and the rodless chamber of the oil cylinder 10; the rod chamber of the oil cylinder 10 is connected to the oil outlet of the first one-way valve 4; the controller 11 is connected to the solenoid valve 3, the first switch valve 5, the second switch valve 6 and the proportional valve 9 signals, and is used to control the states of the solenoid valve 3, the first switch valve 5, the second switch valve 6 and the proportional valve 9.

[0027] In this embodiment, the main control valve 1 serves as the main gate of the system oil, the oil outlet P0 provides pressurized oil to the solenoid valve 3, and the first oil return port T0 and the second oil return port R0 respectively receive return oil from different branches to ensure orderly oil circulation.

[0028] In this embodiment, the solenoid valve 3 is the key to the oil circuit. Its oil outlet is connected to the first one-way valve 4 and the first oil return port T0 of the main control valve 1 at the same time, which can realize the pressure oil guide switching; when energized, the pressure oil is conducted to the first one-way valve 4, and when the power is off, the passage is cut off, and at the same time the oil circuit is connected to the first oil return port of the main control valve 1, thereby realizing the oil circuit switching.

[0029] One end of the first switch valve 5 is connected to the oil outlet of the first one-way valve 4, and the other end is connected to the second switch valve 6 and the second oil return port R0 of the main control valve 1. The other end of the second switch valve 6 is connected to the first oil return port T0 of the main control valve 1. The two cooperate to control the on-off of the oil cylinder 10 and the oil return port. During operation, the first switch valve 5 is closed under the action of pressurized oil to block the passage between the oil cylinder 10 and the oil return port to ensure the pressure of the oil cylinder 10; when not in operation, it is opened to allow the oil in the oil cylinder 10 to return and assist in resetting.

[0030] In this embodiment, the function of the first one-way valve 4 is to prevent the oil from flowing back and damaging the front-end components such as the solenoid valve 3, to ensure the unidirectional delivery of the pressure oil to the subsequent components, and to ensure the pressure stability of the oil circuit.

[0031] In this embodiment, the proportional valve 9 is the core of the lower pressure regulation, and its return oil port is connected to the second return oil port R0 of the main control valve 1. The inlet and outlet are respectively connected to the oil outlet of the first one-way valve 4 and the rodless chamber of the cylinder 10, which can adjust the oil inlet amount of the rodless chamber of the cylinder 10; the rod chamber of the cylinder 10 is directly connected to the oil outlet of the first one-way valve 4, and the expansion and contraction are achieved through the pressure difference between the rodless chamber and the rod chamber.

[0032] In this embodiment, the controller 11 is connected to the solenoid valve 3, the first switch valve 5, the second switch valve 6, and the proportional valve 9 through a signal line. It can output electrical signals in real time, control the on-off and reversing of each valve, coordinate the actions of each component, control the output and return of pressure oil, open the oil supply during operation, cut off the oil source and guide the return oil when shut down, and is the core hub of the system oil flow.

[0033] The application process of the system in the whole cycle of seed drill operation is as follows: Initial state: the main control valve 1 is closed, the solenoid valve 3 and the proportional valve 9 are de-energized, the first switch valve 5 and the second switch valve 6 are opened, the rodless chamber and the rod chamber of the oil cylinder 10 are connected to the first oil return port T0 through the first switch valve 5 and the second switch valve 6, and the oil cylinder 10 is fully extended under the action of the gravity of the sowing unit.

[0034] The oil cylinder 10 retracts: the main control valve 1 opens, the controller 11 controls the solenoid valve 3 to be energized, and the pressure oil enters the rod chamber of the oil cylinder 10 through the solenoid valve 3 and the first one-way valve 4. At the same time, the proportional valve 9 is de-energized, and the pressure in the rod chamber of the oil cylinder 10 increases, pushing the oil cylinder 10 to retract. The oil in the rodless chamber returns through the proportional valve 9 and the second oil return port R0 of the main control valve 1, and the single unit is lifted; Downward pressure control: Main control valve 1 remains open, solenoid valve 3 is continuously energized, and controller 11 controls proportional valve 9 to energize. Pressurized oil enters the rodless chamber of cylinder 10 through first one-way valve 4 and proportional valve 9, pushing cylinder 10 out (single cylinder into the soil). Oil remains in the rod chamber. Controller 11 controls the amount of oil flowing into the rodless chamber by adjusting the current of proportional valve 9, thereby controlling downward pressure and ensuring the depth of soil penetration. Real-time adjustment: When the soil becomes harder and the resistance of the monomer to the soil increases, the controller 11 increases the current of the proportional valve 9 to increase the downward force; when the soil becomes softer, the current is reduced to reduce the downward force and maintain the same depth of soil penetration; Reset state: the main control valve 1 is closed, the controller 11 controls the solenoid valve 3 and the proportional valve 9 to cut off the power, the first switch valve 5 and the second switch valve 6 are opened, the oil in the cylinder 10 returns through the first switch valve 5 and the second switch valve 6, and automatically restores to the fully extended state.

[0035] In an optional embodiment, a filter 2 is provided between the oil outlet of the main control valve 1 and the solenoid valve 3 .

[0036] In this embodiment, the filter 2 is connected in series between the oil outlet of the main control valve 1 and the oil inlet of the solenoid valve 3. Its function is to purify the pressure oil and solve the oil contamination problem in the working environment of the seed drill.

[0037] There is a lot of dust, soil particles and metal debris in the operation scene of the seed drill. If impurities enter the solenoid valve 3, proportional valve 9 and other precision components along with the pressure oil, it will cause the valve core to get stuck and the seals to wear, causing valve failure and loss of control of the downforce. The filter 2 intercepts impurities through the pores of the filter material and only allows clean oil to enter the subsequent oil circuit, ensuring the normal operation of key components such as the solenoid valve 3 and proportional valve 9, and extending the service life of the system.

[0038] In this embodiment, no matter the system is in the state of oil cylinder 10 retraction, downward pressure control or real-time adjustment, the pressure oil output by main control valve 1 must first be filtered by filter 2 before entering solenoid valve 3.

[0039] In an optional embodiment, a first flow valve 7 is provided between the oil outlet of the solenoid valve 3 and the first oil return port T0 of the main control valve 1 .

[0040] In this embodiment, the first flow valve 7 is connected in series between the oil outlet of the solenoid valve 3 and the first oil return port T0 of the main control valve 1 .

[0041] In this embodiment, the core function of the first flow valve 7 is to stabilize the pilot oil return flow rate to avoid hydraulic shock when the system state switches: when the system switches from the working state to the non-working state (solenoid valve 3 is de-energized), the pilot oil that originally pushed the on-off valve to switch direction must flow through the oil outlet of the solenoid valve 3 to the first return oil port T0 for return oil. If the return oil speed is too fast, the on-off valve will switch direction quickly, causing a sudden change in oil circuit pressure, generating impact noise, and even damaging valve components and pipelines. The first flow valve 7 limits the maximum value of the return oil flow rate to make the pilot oil return slowly, ensuring smooth switching of the on-off valve and protecting system components.

[0042] In an optional embodiment, a second flow valve 8 is provided between the second switch valve 6 and the first oil return port T0 of the main control valve 1 .

[0043] In this embodiment, second flow valve 8 is connected in series between the oil outlet of second on-off valve 6 and the first oil return port T0 of main control valve 1. Second flow valve 8 has the same structure as first flow valve 7 and is a throttling flow valve. Its oil inlet is connected to the oil outlet of second on-off valve 6, and its oil outlet is connected to the first oil return port T0 of main control valve 1. By setting the maximum return oil flow rate, it adapts to the required oil return speed of cylinder 10.

[0044] In an optional embodiment, the proportional valve 9 and the oil cylinder 10 constitute a downforce control unit; there are multiple downforce control units, and the multiple downforce control units are connected in parallel.

[0045] In this embodiment, the proportional valve 9 + the oil cylinder 10 are defined as a downforce control unit, and multiple such units are provided, each connected in parallel. The number of downforce control units matches the number of planter units, such as 4 to 6.

[0046] Specifically, in this embodiment, the oil inlet of the proportional valve 9 of each unit is connected in parallel to the oil outlet of the first one-way valve 4 to ensure that the pressure oil source of all units is consistent; at the same time, the oil return port of the proportional valve 9 of each unit is connected in parallel to the first oil return port T0 or the second oil return port R0 of the main control valve 1, and the rod chamber of the oil cylinder 10 is connected in parallel to the oil outlet of the first one-way valve 4.

[0047] In this embodiment, the controller 11 is connected to the proportional valve 9 of each unit through an independent signal line, and can adjust the current of each proportional valve 9 separately.

[0048] In this embodiment, the core function of the multi-unit parallel connection is to achieve independent downforce control of multiple sowing units: The traditional single-unit system cannot distinguish the resistance of different monomers to entering the soil. Uniformly adjusting the downward pressure will cause some monomers to enter the soil too deep (soft soil) and some too shallow (hard soil). After multiple units are connected in parallel, the controller 11 can independently adjust the current of the corresponding proportional valve 9 according to the resistance of each monomer, so that the downward pressure of each monomer adapts to the soil in which it is located, ensuring that the depth of entry of all monomers is consistent, thereby improving sowing accuracy.

[0049] In an optional embodiment, a pressure sensor 13 is provided between the main control valve 1 and the solenoid valve 3 .

[0050] In this embodiment, pressure sensor 13 is connected in parallel between the oil outlet P0 of main control valve 1 and the oil inlet of solenoid valve 3. Pressure sensor 13 utilizes a strain gauge structure, with a pressure detection terminal that directly contacts the pressurized oil and a signal output terminal connected to controller 11. Its measurement range is adapted to the planter hydraulic system pressure, and its accuracy level ensures accurate pressure detection. It converts the pressure signal into an electrical signal in real time and transmits it to controller 11.

[0051] In this embodiment, the core function of the pressure sensor 13 is to monitor the pressure of the main oil circuit in real time, provide pressure feedback to the controller 11, and avoid system pressure out of control; the traditional system has no pressure monitoring. When the main control valve 1 fails and the pressure output is too high, or the oil pump lacks oil and the pressure is too low, the controller 11 cannot perceive it, which may cause the pressure under the cylinder 10 to be too high and damage the unit, or the pressure under the cylinder 10 to be too low and unable to enter the soil; the pressure sensor 13 transmits the detected pressure signal to the controller 11 in real time. The controller 11 can judge the system status according to the signal, realize pressure closed-loop control and fault alarm, and ensure operation safety.

[0052] In an optional embodiment, the solenoid valve 3 is configured to allow the pressure oil to pass through in an energized state, block the pressure oil in an unenergized state, and control the switching of the first switch valve 5 and the second switch valve 6.

[0053] In this embodiment, the solenoid valve 3 is a two-position, two-way solenoid reversing valve, which only contains an oil inlet and an oil outlet, and has a built-in reset spring and an electromagnetic coil. When the power is off, the spring pushes the valve core to block the oil inlet and the oil outlet. When energized, the electromagnetic force overcomes the spring force to conduct the oil circuit; the oil inlet is directly connected to the oil outlet P0 of the main control valve 1 to obtain the pressure oil source; the oil outlet of the solenoid valve 3 is connected to two branches, one branch is directly connected to the oil inlet of the first one-way valve 4, and supplies oil to the main execution oil circuit where the subsequent oil cylinder 10 and the proportional valve 9 are located; the other branch is connected to the oil inlet of the first flow valve 7, and the oil outlet of the first flow valve 7 is finally connected to the first oil return port T0 of the main control valve 1, forming an independent oil return branch.

[0054] When the solenoid valve 3 is energized, the electromagnetic force pushes the valve core to connect the oil inlet and the oil outlet, that is, it is located in position b, and the pressure oil comes out from the oil outlet and is divided into two paths. One path can only flow to the main execution oil circuit due to the one-way conduction characteristic of the first one-way valve 4, providing power for the extension and contraction of the cylinder 10; the other path enters the first flow valve 7; when the solenoid valve 3 is de-energized, the spring pushes the valve core, so that the valve core is located in position a to block the oil circuit, and the main execution oil circuit is cut off from oil.

[0055] In an optional embodiment, when the system is in a non-operating state, the first switch valve 5 and the second switch valve 6 are passages.

[0056] In this embodiment, when the system is in a non-operating state, the first switch valve 5 and the second switch valve 6 are in a passage state, which relieves the pressure of the oil cylinder 10 and ensures that the oil cylinder 10 can be automatically reset without manual reset.

[0057] In an optional embodiment, a second one-way valve 12 is provided on the oil circuit connected to the second oil return port R0 of the main control valve 1 .

[0058] In this embodiment, the second one-way valve 12 is connected in series between the oil return port of the proportional valve 9 and the second oil return port R0 of the main control valve 1, which can effectively prevent the return oil from flowing back and protect the proportional valve 9 and the cylinder 10 from being in a stable state.

[0059] In a second aspect, the present invention provides a tractor comprising the downforce control hydraulic system according to any one of the aforementioned embodiments.

[0060] The beneficial effects of the embodiments of the present invention are: The main control valve 1 is used as the overall oil source control, and the solenoid valve 3, proportional valve 9, etc. are connected in series to form an integrated circuit, replacing the traditional complex mechanical or decentralized hydraulic structure, reducing parts and pipelines, simplifying the structure, and lowering the difficulty of maintenance; the controller 11 outputs electrical signals to control each valve, and the operator does not need to manually adjust on site, realizing remote operation.

[0061] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A downforce control hydraulic system, characterized in that: It includes a main control valve, a controller, a solenoid valve, a first switch valve, a second switch valve, a first one-way valve, a proportional valve and an oil cylinder; The oil outlet of the main control valve is communicated with the oil inlet of the solenoid valve, and the oil outlet of the solenoid valve is connected to the oil inlet of the first one-way valve and the first oil return port of the main control valve; The oil outlet of the first one-way valve is connected to one end of the first switch valve; The other end of the first switch valve is connected to one end of the second switch valve and the second oil return port of the main control valve; The other end of the second switch valve is connected to the first oil return port of the main control valve; The oil return port of the proportional valve is connected to the second oil return port of the main control valve, and the two inlets and outlets of the proportional valve are connected to the oil outlet of the first one-way valve and the rodless chamber of the oil cylinder respectively; The rod chamber of the oil cylinder is connected to the oil outlet of the first one-way valve; The controller is connected to the solenoid valve, the first switch valve, the second switch valve and the proportional valve by signal, and is used to control the states of the solenoid valve, the first switch valve, the second switch valve and the proportional valve.

2. The downforce control hydraulic system according to claim 1, characterized in that: A filter is provided between the oil outlet of the main control valve and the solenoid valve.

3. The downforce control hydraulic system according to claim 1, characterized in that: A first flow valve is provided between the oil outlet of the solenoid valve and the first oil return port of the main control valve.

4. The downforce control hydraulic system according to claim 1, characterized in that: A second flow valve is provided between the second switch valve and the first oil return port of the main control valve.

5. The downforce control hydraulic system according to claim 1, characterized in that: The proportional valve and the oil cylinder constitute a downforce control unit; There are multiple down force control units, and the multiple down force control units are connected in parallel.

6. The downforce control hydraulic system according to claim 1, characterized in that: A pressure sensor is provided between the main control valve and the solenoid valve.

7. The downforce control hydraulic system according to claim 1, characterized in that: The solenoid valve is configured to allow pressure oil to pass through in an energized state, block the pressure oil in an unenergized state, and control the switching of the first switch valve and the second switch valve.

8. The downforce control hydraulic system according to claim 1, characterized in that: When the system is in a non-operating state, the first switch valve and the second switch valve form a passage.

9. The downforce control hydraulic system according to claim 1, characterized in that: A second one-way valve is provided on the oil circuit connected to the second oil return port of the main control valve.

10. A tractor, characterized in that: A downforce control hydraulic system comprising the downforce control hydraulic system according to any one of claims 1 to 9.

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