Hydraulic control system and control method thereof

Abstract

The application relates to the technical field of hydraulic control of engineering machinery, and discloses a hydraulic control system and a control method thereof, which comprise a boom cylinder, a stick cylinder, a bucket cylinder, a boom reversing valve, a stick reversing valve, a bucket reversing valve, a sensor, a solenoid valve and a controller; the controller is electrically connected with two control ends of the boom reversing valve, the stick reversing valve and the bucket reversing valve respectively, the controller is electrically connected with a control end of the solenoid valve, and the controller is in communication connection with the sensor; the sensor is connected with the boom cylinder and is used for collecting pressure of a large cavity and a small cavity of the boom cylinder and a piston rod displacement signal of the boom cylinder; an oil inlet of the solenoid valve is connected with the small cavity of the boom cylinder, and an oil outlet is connected with the large cavity of the boom cylinder. The application has the beneficial effect that the front end of the excavator can be prevented from being raised when the excavator is used for flat ground and digging operations, the whole machine is kept stable, and the operation comfort is improved.

Description

Technical Field

[0001] This invention relates to the field of engineering machinery technology, and specifically to a hydraulic control system and its control method, particularly to a hydraulic control system and its control method for an excavator. Background Technology

[0002] Existing excavators typically have overflow valves in both the large and small boom chambers, with a set value slightly higher than the system's set pressure. Under this overflow pressure, during excavation or heavy-duty leveling operations, the boom generally remains stationary, relying solely on the combined operation of the bucket and stick. However, when the bucket encounters significant resistance during excavation or heavy-duty leveling, the reaction force is transmitted to the boom. Due to the high overflow pressure at the boom cylinder port, the boom cylinder can withstand a large reaction force. This reaction force causes the front of the excavator to tilt up and slightly lift off the ground, resulting in overall machine sway and affecting operational comfort. The force applied is as follows: Figure 1 As shown, the front end of the excavator is tilted upwards as follows: Figure 2 As shown. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a hydraulic control system and its control method, which can prevent the front end of the excavator from tilting up during leveling and excavation operations, maintain the stability of the entire machine, and improve operating comfort.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] In a first aspect, this invention proposes a hydraulic control system, including a boom cylinder, a stick cylinder, a bucket cylinder, a boom directional valve, a stick directional valve, a bucket directional valve, a sensor, a solenoid valve, and a controller; the boom cylinder is connected to the boom directional valve, the stick cylinder is connected to the stick directional valve, and the bucket cylinder is connected to the bucket directional valve; the controller is electrically connected to two control terminals of the boom directional valve, the stick directional valve, and the bucket directional valve, respectively, and is electrically connected to the control terminal of the solenoid valve; the controller is communicatively connected to the sensor; the sensor, connected to the boom cylinder, is used to collect the pressure in the large and small chambers of the boom cylinder and the displacement signal of the boom cylinder piston rod, and... The pressure data and displacement signal are transmitted to the controller. The oil inlet of the solenoid valve is connected to the small chamber of the boom cylinder, and the oil outlet is connected to the large chamber of the boom cylinder. The solenoid valve includes a normally closed working position and a working position. When digging and leveling operations are performed, if the boom directional valve has no pilot pressure or pilot signal, but the bucket directional valve and the stick directional valve have pilot pressure or pilot signal, and the load is greater than the preset load, the controller sends a signal to the solenoid valve to switch to the working position. The controller is also used to send a signal to the solenoid valve, boom directional valve, stick directional valve, and bucket directional valve to change the working position based on the pressure data and displacement signal collected by the sensor and the operator's operation signal.

[0006] In conjunction with the first aspect, the hydraulic system of the present invention further includes a hydraulic oil tank and a main pump. The outlet of the main pump is connected to the inlet C1 of the boom directional valve, the inlet C2 of the stick directional valve, and the inlet C3 of the bucket directional valve, respectively. The outlet A1 of the boom directional valve is connected to the large chamber of the boom cylinder, the small chamber of the boom cylinder is connected to the return port B1 of the boom directional valve, and the outlet D1 of the boom directional valve is connected to the hydraulic oil tank. The outlet A2 of the stick directional valve is connected to the small chamber of the stick cylinder, the large chamber of the stick cylinder is connected to the return port B2 of the stick directional valve, and the outlet D2 of the stick directional valve is connected to the hydraulic oil tank. The outlet A3 of the bucket directional valve is connected to the small chamber of the bucket cylinder, the large chamber of the bucket cylinder is connected to the return port B3 of the bucket directional valve, and the outlet D3 of the bucket directional valve is connected to the hydraulic oil tank.

[0007] In conjunction with the first aspect, the hydraulic system of the present invention further includes a relief valve, the inlet of which is connected to the outlet of the main pump, and the outlet of which is connected to the hydraulic oil tank. The relief valve is used to set the system pressure and protect hydraulic components such as the main pump.

[0008] Meanwhile, the hydraulic system is also equipped with several port relief valves. These port relief valves are respectively located between the boom cylinder and port A1 of the boom directional valve, between the boom cylinder and port B1 of the boom directional valve, between the stick cylinder and port A2 of the stick directional valve, between the stick cylinder and port B2 of the stick directional valve, between the bucket cylinder and port A3 of the bucket directional valve, and between the bucket cylinder and port B3 of the bucket directional valve. The port relief valves are designed to protect the boom cylinder, stick cylinder, and bucket cylinder.

[0009] In conjunction with the first aspect, the hydraulic system of the present invention further includes a check valve assembly, wherein the inlet of the check valve assembly is connected to the hydraulic oil tank, and the outlet is connected to the inlet E of the boom directional valve; the check valve assembly is provided to prevent cavitation in the large chamber of the boom cylinder. When the oil circuits of the large and small chambers of the boom cylinder are connected, the large chamber of the boom cylinder is replenished by, on the one hand, by the hydraulic oil in the small chamber flowing into the large chamber through the solenoid valve, and on the other hand, by the oil circuit of the check valve assembly replenishing the large chamber from the hydraulic oil tank.

[0010] In conjunction with the first aspect, further, the stick reversing valve includes at least three working positions, which are, from left to right, a left working position, a middle working position, and a right working position. The six ports of the middle working position of the stick reversing valve are not interconnected. In the left working position, port C2 is connected to port A2, and port B2 is connected to port D2. In the right working position, port C2 is connected to port B2, and port A2 is connected to port D2. When the valve core of the stick reversing valve is in the left or right working position, the stick cylinder performs a telescopic movement, i.e., the stick retracts and swings outward, meaning the excavator stick is in the working state.

[0011] In conjunction with the first aspect, further, the bucket reversing valve includes at least three working positions, which are, from left to right, a left working position, a middle working position, and a right working position. The six ports of the middle working position of the bucket reversing valve are not interconnected. In the left working position, port C3 is connected to port A3, and port B3 is connected to port D3. In the right working position, port C3 is connected to port B3, and port A3 is connected to port D3. When the valve core of the bucket reversing valve is in the left or right working position, the bucket cylinder performs a telescopic movement, i.e., the boom retracts and swings outward, meaning the excavator bucket is in the working state.

[0012] Preferably, the boom reversing valve is a three-position six-way solenoid reversing valve; the bucket reversing valve is a three-position six-way solenoid reversing valve.

[0013] In conjunction with the first aspect, further, the boom directional valve includes at least three working positions, which are, from left to right, the left working position, the middle working position, and the right working position. In the middle working position, ports A1 and E are connected, while the other ports are not interconnected. In the left working position, ports C1 and A1 are connected, and ports B1 and D1 are connected. In the right working position, ports C1 and B1 are connected, and ports A1 and D1 are connected. After the anti-tilt operation, the boom rises due to the piston rod of the boom cylinder. To maintain the working posture, further compensation of the boom position is required. The controller controls the boom directional valve to be in the right working position. At this time, the main pump injects pressurized oil into the small chamber of the boom cylinder, causing the piston rod to move downwards to the position before the anti-tilt operation.

[0014] Preferably, the boom reversing valve is a three-position six-way solenoid reversing valve.

[0015] In conjunction with the first aspect, the solenoid valve is further described as a two-position two-way solenoid valve, wherein the two oil ports of the upper working position are not interconnected, i.e., normally closed working position; and the two oil ports of the lower working position are interconnected, i.e., open working position.

[0016] In conjunction with the first aspect, the sensor further includes a pressure sensor and a displacement sensor. The pressure sensor is connected to the controller and the large and small chambers of the boom cylinder, respectively, and is used to collect the pressure in the large and small chambers of the boom cylinder and transmit the pressure data to the controller. The displacement sensor is installed on the piston rod of the boom cylinder and is used to collect the displacement data of the boom cylinder piston rod and transmit the displacement data to the controller.

[0017] In conjunction with the first aspect, the boom cylinder can be a single cylinder or a double cylinder.

[0018] Secondly, the present invention proposes a control method for a hydraulic control system, which, based on the aforementioned hydraulic control system, includes the following steps:

[0019] To carry out excavation or leveling operations;

[0020] The sensor collects the pressure P1 in the large chamber of the boom cylinder and the pressure P2 in the small chamber of the boom cylinder in real time, and transmits the collected pressure data to the controller.

[0021] When the boom directional valve has no pilot pressure or pilot signal, but the bucket directional valve and stick directional valve have pilot pressure or pilot signal, the controller compares the pressure data from the sensor with the excavator lift pressure Pm preset in the controller.

[0022] If the load is too large, that is, when the pressure P2 in the small chamber of the boom cylinder is greater than the excavator lifting pressure Pm preset in the controller, the controller sends a control signal to the solenoid valve, causing the valve core of the solenoid valve to move upward and the solenoid valve to be in the conducting position. At this time, the oil circuits of the large chamber and the small chamber of the boom cylinder are connected, the pressure oil in the small chamber flows to the large chamber, and the pressure in the small chamber decreases.

[0023] When the pressure P2 in the small chamber decreases to less than the excavator lifting pressure Pm preset in the controller, the controller sends a control signal to the solenoid valve, causing the valve core of the solenoid valve to move down and the solenoid valve to be in the normally closed working position. At this time, the oil circuits of the large and small chambers of the boom cylinder are closed.

[0024] It should be noted that the excavator tilting pressure Pm preset in the controller is a design parameter of the excavator, which refers to the minimum boom chamber pressure value that can cause the excavator to tilt and affect the operator's experience when only the stick cylinder and bucket cylinder are operated.

[0025] In conjunction with the second aspect, the control method of the present invention further includes the sensor acquiring the displacement value of the piston rod of the boom cylinder relative to the cylinder barrel in real time, and transmitting the displacement value L to the controller.

[0026] In conjunction with the second aspect, the control method of the present invention further includes a boom position compensation method, specifically:

[0027] When the controller detects four simultaneous occurrences—excavator leveling, controller not receiving boom cylinder operation signal from operator, controller sending control signal to solenoid valve to switch to the on position, and controller receiving sensor data indicating boom cylinder piston displacement—boom position compensation is required. The specific compensation method is as follows:

[0028] The controller sends a control signal to the control terminal of the boom reversing valve, causing the boom reversing valve to switch to the right working position. At this time, the small chamber of the boom cylinder receives oil, and the piston rod of the boom cylinder moves down.

[0029] Every Δt time interval, the controller calculates the difference between the real-time displacement value L3 of the boom cylinder piston rod and the displacement value L1 of the boom piston rod before the solenoid valve switches to the conducting working position, and obtains the difference Δl1.

[0030] When the absolute value of Δl1 falls within the set value range [Δl-n, Δl+n], the controller sends a control signal to the boom directional valve, causing the boom directional valve to switch to the middle working position to maintain the position of the boom cylinder at this time.

[0031] In the set value, Δl is the absolute value of the displacement difference obtained by the controller by calculating the difference between the displacement value L1 of the boom cylinder piston rod before the solenoid valve switches to the open working position and the displacement value L2 of the boom cylinder piston rod after the solenoid valve switches to the normally closed working position; in the set value, n is one of the excavator design parameters (n is the revision value of the cylinder displacement difference of excavators of different tonnages. Within the error range, the excavator posture does not affect normal operation). If Δl1 is within the range of [Δl-n, Δl+n], the displacement of the boom cylinder piston rod will not cause the need for position compensation during flat ground operation.

[0032] In conjunction with the second aspect, the boom position compensation behavior occurs Δk time after the solenoid valve switches to the normally closed position, where Δk is a set value based on the commonly used working speed for different tonnages.

[0033] Compared with the prior art, the present invention provides a hydraulic control system and its control method, which has the following beneficial effects:

[0034] (1) The hydraulic control system of the present invention, through the setting of solenoid valves and sensors, enables the reaction force transmitted to the small chamber of the boom cylinder during operation to be released during leveling and excavation, preventing the front end of the excavator from tilting up, maintaining the stability of the whole machine, and improving the comfort of operation.

[0035] (2) The hydraulic control system of the present invention can realize the compensation of boom position on flat ground, so that the driver does not need to readjust the boom working posture, reducing the fatigue intensity of the operator and improving the working efficiency. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the forces acting on an excavator during digging or heavy-duty retraction operations on flat ground in the existing technology.

[0037] Figure 2 This is a schematic diagram showing the front end of an excavator tilting up during digging or heavy-duty leveling operations in the prior art.

[0038] Figure 3 This is a hydraulic schematic diagram of the hydraulic system of the present invention (the boom cylinder in the diagram is a double cylinder).

[0039] The meanings of the reference numerals in the figure are as follows:

[0040] 1-Main pump; 2-Controller; 3-Boom directional valve; 4-Solenoid valve; 5-Boom cylinder; 6-Sensor; 7-Stick cylinder; 8-Stick directional valve; 9-Bucket cylinder; 10-Bucket directional valve; 11-Hydraulic oil tank; 12-Check valve assembly; 13-Relief valve. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may include different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0043] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only used to facilitate the description of the present invention and to simplify the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of the present invention.

[0044] like Figure 3 As shown, the hydraulic system proposed in this invention includes a boom cylinder 5, a stick cylinder 7, a bucket cylinder 9, a boom directional valve 3, a stick directional valve 8, a bucket directional valve 10, a sensor 6, a solenoid valve 4, and a controller 2. The boom cylinder 5 is connected to the boom directional valve 3, the stick cylinder 7 is connected to the stick directional valve 8, and the bucket cylinder 9 is connected to the bucket directional valve 10. The controller 2 is electrically connected to two control terminals of the boom directional valve 3, the stick directional valve 8, and the bucket directional valve 10, respectively. The controller 2 is also electrically connected to the control terminal of the solenoid valve 4, and the controller 2 is communicatively connected to the sensor 6. The sensor 6 is connected to the boom cylinder 5... The connection is used to collect the pressure of the large and small chambers of the boom cylinder 5 and the displacement signal of the piston rod of the boom cylinder 5, and transmit the pressure data and displacement signal to the controller 2; the oil inlet of the solenoid valve 4 is connected to the small chamber of the boom cylinder 5, and the oil outlet is connected to the large chamber of the boom cylinder 5. The solenoid valve 4 includes a normally closed working position and a conducting working position. When digging and leveling operations are performed, if the boom reversing valve 3 has no pilot pressure or pilot signal, and the bucket reversing valve 10 and the stick reversing valve 8 have pilot pressure or pilot signal, and the load is greater than the preset load, the controller 2 sends a signal to the solenoid valve 4 to switch to the conducting working position; the controller 2 is also used to send a signal to the solenoid valve 4, the boom reversing valve 3, the stick reversing valve 8, and the bucket reversing valve 10 to change the working position according to the pressure data and displacement signal collected by the sensor 6 and the operation signal of the operator.

[0045] In one specific embodiment of this invention, the hydraulic system further includes a hydraulic oil tank 11 and a main pump 1. The outlet of the main pump 1 is connected to the inlet C1 of the boom directional valve 3, the inlet C2 of the stick directional valve 8, and the inlet C3 of the bucket directional valve 10, respectively. The outlet A1 of the boom directional valve 3 is connected to the large chamber of the boom cylinder 5, the small chamber of the boom cylinder 5 is connected to the return port B1 of the boom directional valve 3, and the outlet D1 of the boom directional valve 3 is connected to the hydraulic oil tank 11. The outlet A2 of the stick directional valve 8 is connected to the small chamber of the stick cylinder 7, and the large chamber of the stick cylinder 7 is connected to the return port B2 of the stick directional valve 8. The stick reversing valve 8 is connected to the hydraulic oil tank 11 via its outlet port D2; the bucket reversing valve 10 is connected to the small chamber of the bucket cylinder 9 via its outlet port A3; the bucket cylinder 9 is connected to the return port B3 of the bucket reversing valve 10 via its large chamber; and the bucket reversing valve 10 is connected to the hydraulic oil tank 11 via its outlet port D3.

[0046] In one specific embodiment of this invention, the hydraulic system of the present invention further includes a relief valve 13. The oil inlet of the relief valve 13 is connected to the oil outlet of the main pump 1, and the oil outlet of the relief valve 13 is connected to the hydraulic oil tank 11. The relief valve 13 sets the system pressure and protects the main pump and other hydraulic components.

[0047] Meanwhile, the hydraulic system is also equipped with several port relief valves, which are respectively located between the boom cylinder 5 and the boom directional valve 3 (port A1), between the boom cylinder 5 and the boom directional valve 3 (port B1), between the stick cylinder 7 and the stick directional valve 8 (port A2), between the stick cylinder 7 and the stick directional valve 8 (port B2), between the bucket cylinder 9 and the bucket directional valve 10 (port A3), and between the bucket cylinder 9 and the bucket directional valve 10 (port B3). The port relief valves are used to protect the boom cylinder 5, the stick cylinder 7, and the bucket cylinder 9.

[0048] In one specific embodiment of this invention, the hydraulic system of the present invention further includes a one-way valve assembly 12. The inlet of the one-way valve assembly 12 is connected to the hydraulic oil tank 11, and the outlet is connected to the inlet E of the boom reversing valve 3. The one-way valve assembly 12 is provided to prevent the large chamber of the boom cylinder 5 from sucking in air. When the oil circuits of the large and small chambers of the boom cylinder 5 are connected, the large chamber of the boom cylinder 5 is replenished by, on the one hand, by the hydraulic oil from the small chamber flowing into the large chamber through the solenoid valve 4; and on the other hand, by the oil circuit of the one-way valve assembly 12 replenishing the large chamber from the hydraulic oil tank 11.

[0049] The operating principle of the one-way valve assembly 12 in this hydraulic system is as follows: When the anti-tilt operation is performed, the solenoid valve 4 is in the open working position, and the pressure oil in the small chamber of the boom cylinder 5 enters the large chamber. At this time, the piston of the boom cylinder 5 moves upward. Since the working area of ​​the large chamber of the cylinder is larger than that of the small chamber, when the amount of pressure oil flowing from the small chamber into the large chamber is insufficient to support the cylinder to move to the corresponding position, it is necessary to replenish oil from the hydraulic oil tank 11. The one-way valve assembly 12 includes a one-way valve and a throttle valve (actually a throttle orifice). The existence of the throttle orifice can limit the replenishment speed from the hydraulic oil tank 11, thereby preventing the boom cylinder 5 from moving too fast during the anti-tilt operation. On the one hand, the one-way valve allows the large chamber of the boom to be replenished from the hydraulic oil tank, and on the other hand, it prevents the boom from falling off when the excavator is working, thus playing the role of a holding valve.

[0050] In one specific embodiment of this invention, the stick reversing valve 8 includes at least three working positions, which are, from left to right, a left working position, a middle working position, and a right working position. The six ports of the middle working position of the stick reversing valve 8 are not interconnected. Port C2 of the left working position is connected to port A2, and port B2 is connected to port D2. Port C2 of the right working position is connected to port B2, and port A2 is connected to port D2. When the valve core of the stick reversing valve 8 is in the left or right working position, the stick cylinder 7 performs a telescopic movement, i.e., the stick retracts and swings outward, meaning the excavator's stick is in the working state.

[0051] In one specific embodiment of this invention, the bucket directional valve 10 includes at least three working positions, which are, from left to right, a left working position, a middle working position, and a right working position. The six ports of the middle working position of the bucket directional valve 10 are not interconnected. Port C3 of the left working position is connected to port A3, and port B3 is connected to port D3. Port C3 of the right working position is connected to port B3, and port A3 is connected to port D3. When the valve core of the bucket directional valve 10 is in the left or right working position, the bucket cylinder 9 performs a telescopic movement, i.e., the boom retracts and swings outward, meaning the excavator bucket is in working condition.

[0052] Preferably, the boom reversing valve 8 is a three-position six-way solenoid reversing valve; the bucket reversing valve 10 is a three-position six-way solenoid reversing valve.

[0053] In one specific embodiment of this example, the boom directional valve 3 includes at least three working positions, which are, from left to right, the left working position, the middle working position, and the right working position. In the middle working position, ports A1 and E are connected, while the other ports are not interconnected. In the left working position, ports C1 and A1 are connected, and ports B1 and D1 are connected. In the right working position, ports C1 and B1 are connected, and ports A1 and D1 are connected. After the anti-tilt operation, the boom rises due to the piston rod of the boom cylinder 5. To maintain the working posture, further compensation of the boom position is required. The controller 2 controls the boom directional valve 3 to be in the right working position. At this time, the main pump 1 injects pressurized oil into the small chamber of the boom cylinder 5, causing the piston rod to move downwards to the position before the anti-tilt operation.

[0054] Preferably, the boom reversing valve 3 is a three-position six-way solenoid reversing valve.

[0055] In one specific embodiment of this example, the solenoid valve 4 is a two-position two-way solenoid valve 4, with the two oil ports of the upper working position not connected to each other, i.e., the normally closed working position; and the two oil ports of the lower working position connected to each other, i.e., the open working position.

[0056] In one specific embodiment of this example, sensor 6 includes a pressure sensor and a displacement sensor. The pressure sensor is connected to the controller 2 and the large and small chambers of the boom cylinder 5, respectively, and is used to collect the pressure in the large and small chambers of the boom cylinder 5 and transmit the pressure data to the controller 2. The displacement sensor is disposed on the piston rod of the boom cylinder 5 and is used to collect the displacement data of the piston rod of the boom cylinder 5 and transmit the displacement data to the controller 2.

[0057] In one specific embodiment of this example, the boom cylinder 5 can be a single cylinder or a double cylinder.

[0058] This invention also proposes a control method for a hydraulic control system, based on the aforementioned hydraulic system, comprising the following steps:

[0059] To carry out excavation or leveling operations;

[0060] Sensor 6 collects the pressure P1 of the large chamber of boom cylinder 5 and the pressure P2 of the small chamber of boom cylinder 5 in real time, and transmits the collected pressure data to controller 2.

[0061] When the boom reversing valve 3 has no pilot pressure or pilot signal, while the bucket reversing valve 10 and the stick reversing valve 8 have pilot pressure or pilot signal, the controller 2 compares the pressure data from the sensor 6 with the excavator lifting pressure Pm preset in the controller 2.

[0062] If the load is too large, that is, when the pressure P2 in the small chamber of the boom cylinder 5 is greater than the excavator lifting pressure Pm preset in the controller 2, the controller 2 sends a control signal to the solenoid valve 4, causing the valve core of the solenoid valve 4 to move upward and the solenoid valve 4 to be in the conducting working position. At this time, the oil circuits of the large chamber and the small chamber of the boom cylinder 5 are connected, the pressure oil in the small chamber flows to the large chamber, and the pressure in the small chamber decreases.

[0063] When the pressure P2 in the small chamber decreases to less than the excavator lifting pressure Pm preset in the controller 2, the controller 2 sends a control signal to the solenoid valve 4, causing the valve core of the solenoid valve 4 to move down and the solenoid valve 4 to be in the normally closed working position. At this time, the oil circuits of the large chamber and the small chamber of the boom cylinder 5 are closed.

[0064] It should be noted that the excavator tilting pressure Pm preset in controller 2 is a design parameter of the excavator, which refers to the minimum boom chamber pressure value that can cause the excavator to tilt and affect the operator's experience when only the stick cylinder 7 and bucket cylinder 9 are operated.

[0065] In one specific embodiment of this invention, the control method of the present invention further includes sensor 6 acquiring the displacement value of the piston rod of boom cylinder 5 relative to the cylinder barrel in real time, and transmitting the displacement value L to controller 2.

[0066] In one specific embodiment of this invention, the control method further includes a boom position compensation method, specifically:

[0067] When controller 2 detects that the excavator is performing leveling work, controller 2 does not receive an operation signal from the operator for boom cylinder 5, controller 2 sends a control signal to solenoid valve 4 to switch to the on working position, and controller 2 receives a sensor 6 indicating that the piston of boom cylinder 5 has shifted, the boom position needs to be compensated. The specific compensation method is as follows:

[0068] The controller 2 sends a control signal to the control end of the boom reversing valve 3, causing the boom reversing valve 3 to switch to the right working position. At this time, the small chamber of the boom cylinder 5 is filled with oil, and the piston rod of the boom cylinder 5 moves down.

[0069] Every Δt time interval, controller 2 calculates the difference between the real-time displacement value L3 of the boom cylinder 5 piston rod and the displacement value L1 of the boom piston rod before the solenoid valve 4 switches to the conducting working position, and obtains the difference Δl1.

[0070] When the absolute value of Δl1 falls within the set value range [Δl-n, Δl+n], the controller 2 sends a control signal to the boom reversing valve 3, causing the boom reversing valve 3 to switch to the middle working position to maintain the position of the boom cylinder 5 at this time.

[0071] In one specific embodiment of this example, the set value Δl is the absolute value of the displacement difference obtained by the controller 2 through the difference calculation of the displacement value L1 of the boom cylinder 5 piston rod before the solenoid valve 4 switches to the conducting working position and the displacement value L2 of the boom cylinder 5 piston rod after the solenoid valve 4 switches to the normally closed working position; the set value n is the revision value of the displacement difference of the excavator cylinder for different tonnages. Within the error range, the excavator posture does not affect normal operation. Δl and n are both one of the excavator design parameters. If Δl1 is within the range of [Δl-n, Δl+n], the displacement of the boom cylinder 5 piston rod will not cause the need for position compensation during flat ground operation.

[0072] In one specific embodiment of this example, the boom position compensation occurs Δk time after the solenoid valve switches to the normally closed position, where Δk is a set value based on the commonly used working speed for different tonnages.

[0073] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hydraulic control system, characterized in that: The system includes a boom cylinder, stick cylinder, bucket cylinder, boom directional valve, stick directional valve, bucket directional valve, sensor, solenoid valve, and controller. The boom cylinder is connected to the boom directional valve, the stick cylinder to the stick directional valve, and the bucket cylinder to the bucket directional valve. The controller is electrically connected to two control terminals of each of the boom directional valve, stick directional valve, and bucket directional valve, and is also electrically connected to the control terminal of the solenoid valve. The controller is communicatively connected to the sensor. The sensor, connected to the boom cylinder, is used to collect pressure signals from the large and small chambers of the boom cylinder and the piston rod displacement signal, and transmits the pressure and displacement data to the controller. The solenoid valve's inlet is connected to the small chamber of the boom cylinder, and its outlet is connected to the large chamber. The solenoid valve includes normally closed... The boom directional valve and the stick directional valve are configured to operate in the following ways: When excavation and leveling operations are underway, if the boom directional valve has no pilot pressure or pilot signal, but the bucket directional valve and the stick directional valve have pilot pressure or pilot signal, and the load exceeds the preset load, the controller sends a signal to the solenoid valve to switch to the stick directional valve position. The controller also sends signals to the solenoid valve, boom directional valve, stick directional valve, and bucket directional valve to change the operating position based on pressure data and displacement signals collected by sensors and operator input signals. The boom directional valve's outlet port A1 is connected to the large chamber of the boom cylinder. The system also includes a check valve assembly, whose inlet is connected to the hydraulic oil tank, and whose outlet is connected to the boom directional valve's inlet port E. The boom directional valve's operating position ports A1 and E are connected, while the other ports are not interconnected.

2. A hydraulic control system according to claim 1, characterized in that: It also includes a hydraulic oil tank and a main pump. The outlet of the main pump is connected to the inlet C1 of the boom directional valve, the inlet C2 of the stick directional valve, and the inlet C3 of the bucket directional valve, respectively. The small chamber of the boom cylinder is connected to the return port B1 of the boom directional valve, and the outlet D1 of the boom directional valve is connected to the hydraulic oil tank. The outlet A2 of the stick directional valve is connected to the small chamber of the stick cylinder, the large chamber of the stick cylinder is connected to the return port B2 of the stick directional valve, and the outlet D2 of the stick directional valve is connected to the hydraulic oil tank. The outlet A3 of the bucket directional valve is connected to the small chamber of the bucket cylinder, the large chamber of the bucket cylinder is connected to the return port B3 of the bucket directional valve, and the outlet D3 of the bucket directional valve is connected to the hydraulic oil tank.

3. A hydraulic control system according to claim 1, characterized in that: It also includes an overflow valve, the oil inlet of which is connected to the oil outlet of the main pump, and the oil outlet of which is connected to the hydraulic oil tank.

4. A hydraulic control system according to claim 1, characterized in that: The six ports of the boom reversing valve are not interconnected in the working position; port C2 and port A2 are connected in the left working position, and port B2 and port D2 are connected; port C2 and port B2 are connected in the right working position, and port A2 and port D2 are connected.

5. A hydraulic control system according to claim 1, characterized in that: The six ports of the bucket reversing valve in the working position are not interconnected; port C3 in the left working position is connected to port A3, and port B3 is connected to port D3; port C3 in the right working position is connected to port B3, and port A3 is connected to port D3.

6. A hydraulic control system according to claim 1, characterized in that: The boom reversing valve has oil port C1 connected to oil port A1 and oil port B1 connected to oil port D1 in the left working position; and oil port C1 connected to oil port B1 and oil port A1 connected to oil port D1 in the right working position.

7. A control method for a hydraulic control system, characterized in that: The hydraulic control system according to any one of claims 1 to 6 includes the following steps: To carry out excavation or leveling operations; The sensor collects the pressure P1 in the large chamber of the boom cylinder and the pressure P2 in the small chamber of the boom cylinder in real time, and transmits the collected pressure data to the controller. When the boom directional valve has no pilot pressure or pilot signal, but the bucket directional valve and stick directional valve have pilot pressure or pilot signal, the controller compares the pressure data from the sensor with the excavator lift pressure Pm preset in the controller. If the load is too large, that is, when the pressure P2 in the small chamber of the boom cylinder is greater than the excavator lifting pressure Pm preset in the controller, the controller sends a control signal to the solenoid valve, causing the valve core of the solenoid valve to move upward and the solenoid valve to be in the conducting position. At this time, the oil circuits of the large chamber and the small chamber of the boom cylinder are connected, the pressure oil in the small chamber flows to the large chamber, and the pressure in the small chamber decreases. When the pressure P2 in the small chamber decreases to less than the excavator lifting pressure Pm preset in the controller, the controller sends a control signal to the solenoid valve, causing the valve core of the solenoid valve to move down and the solenoid valve to be in the normally closed working position. At this time, the oil circuits of the large and small chambers of the boom cylinder are closed.

8. The control method for a hydraulic control system according to claim 7, characterized in that: It also includes the sensor acquiring the displacement value of the piston rod of the boom cylinder relative to the cylinder barrel in real time, and transmitting the displacement value L to the controller.

9. The control method for a hydraulic control system according to claim 8, characterized in that: It also includes boom position compensation methods, specifically: When the controller detects four simultaneous occurrences—excavator leveling, controller not receiving boom cylinder operation signal from operator, controller sending control signal to solenoid valve to switch to the on position, and controller receiving sensor data indicating boom cylinder piston displacement—boom position compensation is required. The specific compensation method is as follows: The controller sends a control signal to the control terminal of the boom reversing valve, causing the boom reversing valve to switch to the right working position. At this time, the small chamber of the boom cylinder receives oil, and the piston rod of the boom cylinder moves down. Every ∆t time interval, the controller calculates the difference between the real-time displacement value L3 of the boom cylinder piston rod and the displacement value L1 of the boom piston rod before the solenoid valve switches to the conducting working position, and obtains the difference ∆l1. When the absolute value of ∆l1 falls within the set value range [∆ln, ∆l+n], the controller sends a control signal to the boom directional valve, causing the boom directional valve to switch to the intermediate working position to maintain the current position of the boom cylinder; in the set value, ∆l is the absolute value of the displacement difference obtained by the controller by calculating the difference between the received boom cylinder piston rod displacement value L1 before the solenoid valve switches to the open working position and the boom cylinder piston rod displacement value L2 after the solenoid valve switches to the normally closed working position; in the set value, n is the revision value of the cylinder displacement difference for excavators of different tonnages.

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