A hydraulic system and control method for a feller head of a feller-buncher

Abstract

The present application relates to the technical field of forestry machinery hydraulic system and control, and particularly relates to a hydraulic system and control method of a logging head of a logging machine. The present application adopts a hydraulic system of an electric control displacement load sensitive hydraulic pump + combined main valve to control the logging head; each action execution pressure is converted into a signal of a pressure sensor, and a proportional overflow valve pressure is controlled according to the pressure signal, so as to control the load sensitive port pressure of a load sensitive control valve of the hydraulic pump; the present application cancels the load sensitive feedback pipeline, and can realize long distance fast control. The variable control valve group integrates an electric proportional control valve and a load sensitive control valve, can control the oil return path of a variable control mechanism of the hydraulic pump, and the electric proportional control valve can proportionally control the displacement of the hydraulic pump.

Description

Technical Field

[0001] This invention relates to the field of hydraulic systems and control technology for forestry machinery, specifically to a hydraulic system and control method for the harvesting head of a logging machine. Background Technology

[0002] my country's forestry resources are widely distributed. Traditional logging machines mostly use hydraulic excavators as the main unit. The logging head control system uses the system that is built into the logging head. Because the systems of the hydraulic excavator and the logging head are independent of each other, there is no data transmission and good matching control. The movements are not precise, and there are technical problems that cannot meet the execution requirements of different actuators. Summary of the Invention

[0003] The purpose of this invention is to provide a hydraulic system and control method for a logging machine harvesting head, which uses a corresponding control strategy to control the valve core position of the load-sensitive control valve and the electro-proportional control valve when supplying oil to the first or second actuator, so as to meet the execution requirements of the action.

[0004] In a first aspect, the present invention provides a hydraulic system for a logging machine harvesting head, comprising: The hydraulic pump's outlet is connected to the first pressure sensor. The pressure control valve assembly has its P port connected to the oil outlet of the hydraulic pump, and its P port is connected in parallel to the LS port of the electro-proportional relief valve and the pressure control valve assembly. The main valve has its P port connected to the outlet of the hydraulic pump, and its P port is connected in parallel to the electro-proportional directional valve group and the load-sensitive valve group. Its LS port is connected to the second pressure sensor. The electro-proportional directional valve group is used to supply oil to the first actuator, and the load-sensitive valve group is used to supply oil to the second actuator. The variable control valve assembly includes a load-sensitive control valve and an electro-proportional control valve located on the control oil circuit of the variable control mechanism of the hydraulic pump. The left end of the load-sensitive control valve is connected to the oil outlet of the hydraulic pump, and the right end is connected to the LS port of the pressure control valve assembly. The output flow rate of the hydraulic pump can be controlled by controlling the valve core position of the load-sensitive control valve and the electro-proportional control valve. The controller is communicatively connected to the first pressure sensor, the electro-proportional relief valve, the electro-proportional control valve, the electro-proportional directional valve group, the load-sensitive valve group, and the second pressure sensor.

[0005] Optionally, the variable displacement control mechanism of the hydraulic pump includes an upper variable cylinder and a lower variable cylinder. When oil enters the upper variable cylinder and oil returns from the lower variable cylinder, the displacement of the hydraulic pump increases.

[0006] Optionally, the upper port of the load-sensitive control valve is connected to the lower variable cylinder, the first lower port is connected to the outlet of the hydraulic pump, and the second lower port is connected to the upper port of the electro-proportional control valve; the left and right ends of the load-sensitive control valve are respectively connected to the outlet of the hydraulic pump and the LS port of the pressure control valve group; the port pressure of the LS port of the pressure control valve group can be controlled by controlling the control current of the electro-proportional relief valve. The load-sensitive control valve includes a left position and a right position; when the load-sensitive control valve is in the left position, the first lower oil port of the load-sensitive control valve is unidirectionally connected to the upper oil port, and the second lower oil port is closed; when the load-sensitive control valve is in the right position, the second lower oil port of the load-sensitive control valve is bidirectionally connected to the upper oil port; the valve core position of the load-sensitive control valve is determined by the pressure of the hydraulic pump outlet and the LS port of the pressure control valve group.

[0007] Optionally, the first lower port of the electro-proportional control valve is connected to the outlet port of the hydraulic pump, and the second lower port is connected to the return port on the hydraulic pump housing; the electro-proportional control valve includes a left position and a right position; when the electro-proportional control valve is in the left position, the first lower port is closed, and the second lower port and the upper port are bidirectionally connected; when the electro-proportional control valve is in the right position, the first lower port and the upper port are unidirectionally connected; the valve core position of the electro-proportional control valve can be adjusted by controlling the control current of the electro-proportional control valve; when the load-sensitive control valve is in the right position, the output displacement of the hydraulic pump can be proportionally adjusted by controlling the control current of the electro-proportional control valve.

[0008] Optionally, the pressure control valve assembly further includes: The throttling orifice is located between the P port of the pressure control valve assembly and the oil inlet of the electro-proportional relief valve.

[0009] Optionally, the pressure control valve assembly further includes: The safety valve is connected to the P port of the pressure control valve assembly. The oil outlets of both the safety valve and the electro-proportional relief valve are connected to the hydraulic oil tank through the T port of the pressure control valve assembly.

[0010] Optionally, the first actuator includes a feeding motor and a sawing motor; The inlet of the electro-proportional directional valve assembly is connected to the P port of the main valve, the upper A port and the upper B port are respectively connected to the inlet and outlet of the feed motor 5, and the lower A port and the lower B port are respectively connected to the inlet and outlet of the sawing motor 10. By switching the valve position of the electro-proportional directional valve, the electro-proportional directional valve can supply oil to the feed motor or the sawing motor.

[0011] Optionally, the second actuator includes a tilting hydraulic cylinder and a rotary motor; the load-sensitive valve group includes a first working link connected to the tilting hydraulic cylinder and a second working link connected to the rotary motor.

[0012] Optionally, the main valve further includes: The pressure reducing valve has its inlet connected to the P port of the main valve and its outlet connected to the pilot control terminal of the electro-proportional directional valve and the load-sensitive valve group.

[0013] Secondly, the present invention provides a control method for the hydraulic system of a logging machine harvesting head, which is based on the hydraulic system of the logging machine harvesting head, the control method comprising: When neither the first nor the second actuator is activated, the hydraulic pump operates in a preset low-pressure, low-displacement state; both the first and second pressure sensors are in standby pressure. When the first actuator needs to operate, the first control strategy is executed. The first control strategy includes: the controller controls the pilot proportional solenoid valve associated with the first actuator to be energized according to the input action signal of the electro-proportional directional valve group; the control current of the electro-proportional control valve is determined according to the feedback current of the proportional solenoid valve; at the same time, the controller controls the electro-proportional relief valve of the pressure control valve group to be energized, the load-sensitive control valve is in the right position, and the displacement of the hydraulic pump is proportional to the control current of the electro-proportional control valve. When the second actuator needs to operate, the second control strategy is executed. The second control strategy includes: the controller controls the pilot proportional solenoid valve associated with the load-sensitive valve group and the second actuator to be energized according to the input action signal; the controller controls the control current of the electro-proportional control valve and the electro-proportional relief valve with the pressure difference detected by the first pressure sensor and the second pressure sensor being kept at a set value as the target. When the first actuator and the second actuator need to perform a combined action, the control current of the electro-proportional control valve is first determined according to the first strategy, and then the current is increased based on the control current of the electro-proportional control valve determined by the first strategy so that the pressure difference detected by the first pressure sensor and the second pressure sensor is maintained at the set value.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The variable control valve group of the present invention includes a load-sensitive control valve and an electro-proportional control valve located on the control oil circuit of the variable control mechanism of the hydraulic pump. The left end of the load-sensitive control valve is connected to the outlet of the hydraulic pump, and the right end is connected to the LS port of the pressure control valve group. By controlling the valve core positions of the load-sensitive control valve and the electro-proportional control valve, the output flow of the hydraulic pump can be controlled to meet the control requirements for action execution. For the first actuator (e.g., a feeding and sawing motor, which requires a large flow and high control precision), a first control strategy is adopted. The controller controls the pilot proportional solenoid valve associated with the first actuator in the electro-proportional directional valve group to be energized according to the input action signal. The control current of the electro-proportional control valve is determined according to the feedback current of the proportional solenoid valve. At the same time, the controller controls the electro-proportional relief valve of the pressure control valve group to be energized, the load-sensitive control valve is in the right position, and the displacement of the hydraulic pump is proportional to the control current of the electro-proportional control valve. By controlling the control current of the electro-proportional control valve (corresponding to the valve core opening), the output displacement of the hydraulic pump can be proportionally adjusted. The output flow of the hydraulic pump is precisely controlled to meet the control accuracy requirements of the first actuator. For the second actuator (tilting hydraulic cylinder 6, rotary motor 7, or other actuator 8), the control accuracy requirement is not high, and the main requirement is to maintain pressure), a second control strategy is adopted. The controller controls the pilot proportional solenoid valve associated with the load-sensitive valve group and the second actuator to be energized according to the input action signal. The controller aims to maintain the pressure difference detected by the first pressure sensor and the second pressure sensor at a set value, and controls the control current of the electro-proportional control valve and the electro-proportional relief valve to meet the pressure maintenance requirements of the second actuator. Attached Figure Description

[0015] Figure 1 Hydraulic schematic diagram of the hydraulic system of the logging head of the logging machine provided in the embodiment of the present invention; Figure 2 for Figure 1 Hydraulic schematic diagram of a medium-sized hydraulic pump; Figure 3 This is a control architecture diagram of the hydraulic system of the logging head of a logging machine provided in an embodiment of the present invention.

[0016] The following are the labels in the diagram: 1. Hydraulic pump; 2. Pressure control valve assembly; 3. First pressure sensor; 4. Main valve; 5. Feeding motor; 6. Tilting hydraulic cylinder; 7. Rotary motor; 8. Other actuators; 9. Second pressure sensor; 10. Sawing motor; 11. Load-sensitive control valve; 12. Electro-proportional control valve. Detailed Implementation

[0017] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying 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, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0019] To make the purpose, technical solution, and advantages of this invention patent clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] Combination Figure 1 The present invention discloses a hydraulic system for a logging machine harvesting head, which includes a hydraulic pump 1, a pressure control valve group 2, a first pressure sensor 3, a main valve 4, a feeding motor 5, a tilting hydraulic cylinder 6, a rotary motor 7, other actuators 8, a second pressure sensor 9, and a sawing motor 10.

[0021] The oil outlet A of the hydraulic pump 1 is connected to the P port of the main valve 4, the M port of the hydraulic pump 1 is connected to the P port of the pressure control valve group 2, and the X port of the hydraulic pump 1 is connected to the LS port of the pressure control valve group 2; the oil outlet A of the hydraulic pump 1 is connected to the first pressure sensor 3, and the LS1 port of the main valve 4 is connected to the second pressure sensor 9.

[0022] The variable displacement control mechanism of the hydraulic pump 1 includes an upper variable displacement cylinder and a lower variable displacement cylinder. When oil enters the upper variable displacement cylinder and returns oil to the lower variable displacement cylinder, the displacement of the hydraulic pump 1 increases. The oil outlet of the hydraulic pump 1 is connected to the upper variable displacement cylinder through a throttle orifice, which allows the hydraulic pump 1 to change to a larger displacement. The left end of the lower variable displacement cylinder is connected to the housing of the hydraulic pump 1, and the right end spring chamber is connected to the upper oil port of the load-sensitive control valve 11.

[0023] The pressure control valve assembly 2 includes an electro-proportional relief valve and a safety valve. The P port of the pressure control valve assembly 2 is divided into two paths: one path goes through a throttle orifice to the LS port of the pressure control valve assembly 2 and the oil inlet of the electro-proportional relief valve; the other path connects to the oil inlet of the safety valve. The oil outlets of the electro-proportional relief valve and the safety valve are connected together to the T port of the pressure control valve assembly 2 back to the hydraulic oil tank.

[0024] The hydraulic pump 1 is an electronically controlled displacement load-sensitive pump, combined with... Figure 2 The variable displacement control valve group of the hydraulic pump 1 includes a load-sensitive control valve 11 and an electro-proportional control valve 12. The upper port of the load-sensitive control valve 11 is connected to the lower variable displacement cylinder, the first lower port is connected to the outlet of the hydraulic pump 1, and the second lower port is connected to the upper port of the electro-proportional control valve 12. The left and right ends of the load-sensitive control valve 11 are respectively connected to the outlet of the hydraulic pump 1 and the LS port of the pressure control valve group 2. The load-sensitive control valve 11 has a left position and a right position. When the load-sensitive control valve 11 is in the left position, the first lower port and the upper port of the load-sensitive control valve 11 are unidirectionally connected, and the second lower port is closed. When the load-sensitive control valve 11 is in the right position, the second lower port and the upper port of the load-sensitive control valve 11 are bidirectionally connected. The valve core position of the load-sensitive control valve 11 is determined by the pressure of the outlet of the hydraulic pump 1 and the LS port of the pressure control valve group 2. The oil port pressure at the LS port of the pressure control valve assembly 2 can be controlled by controlling the control current of the electro-proportional relief valve. When the electro-proportional control valve 12 is energized, the load-sensitive control valve 11 can compare the pressure difference between the oil outlet of the hydraulic pump 1 connected to the left end and the LS port of the pressure control valve assembly 2 connected to the right end, and maintain the pressure difference between the two sides. ∆ p can maintain a stable output flow rate of variable pump 1. If the pressure difference ∆ As pressure p increases, the valve core of the load-sensitive control valve 11 moves to the left. The hydraulic oil output from the hydraulic pump 1 passes through the load-sensitive control valve 11, causing the lower variable cylinder to receive oil. Therefore, the hydraulic pump 1 will change towards a smaller displacement. If the pressure difference... ∆ As p decreases, the valve core of the load-sensitive control valve 11 moves to the right, and the pilot oil of the lower variable cylinder returns through the load-sensitive control valve 11 and the electro-proportional control valve 12. The hydraulic pump 1 will then move towards the larger displacement until it returns to a balanced state.

[0025] The first lower port of the electro-proportional control valve 12 is connected to the outlet port of the hydraulic pump 1, and the second lower port is connected to the return port on the housing of the hydraulic pump 1. The right end of the electro-proportional control valve 12 is connected to the variable displacement servo piston of the hydraulic pump 1 via a spring to achieve variable displacement control. The electro-proportional control valve 12 includes a left position and a right position. When the electro-proportional control valve 12 is in the left position, the first lower port is closed, and the second lower port and the upper port are bidirectionally connected. When the electro-proportional control valve 12 is in the right position, the first lower port and the upper port are unidirectionally connected. The valve core position of the electro-proportional control valve 12 can be adjusted by controlling the control current of the electro-proportional control valve 12. When the load-sensitive control valve 11 is in the right position, the output displacement of the hydraulic pump 1 can be proportionally adjusted by controlling the control current of the electro-proportional control valve 12.

[0026] When the electro-proportional control valve 12 is energized, the hydraulic pump 1 can adjust its displacement by controlling the load-sensitive control valve 11. When the load-sensitive control valve 11 is in the right position, the displacement of the hydraulic pump 1 can be proportionally controlled by controlling the control current of the electro-proportional control valve 12. The load-sensitive control valve 11 can control the displacement of the hydraulic pump 1 by controlling the load pressure. The control oil circuit needs to pass through the electro-proportional control valve 12 to adjust the displacement of the hydraulic pump 1 to the size required by the actuator. When the load-sensitive control valve 11 is in the right position, within the control range of the hydraulic pump 1, the output flow of the hydraulic pump 1 can be proportionally adjusted by controlling the control current of the electro-proportional control valve 12. The output flow of the hydraulic pump 1 is not affected by the load pressure.

[0027] The P port of the main valve 4 is connected to the oil outlet of the hydraulic pump 1. The P port is connected in parallel to the left electro-proportional directional valve group and the right load-sensitive valve group. The electro-proportional directional valve group is used to supply oil to the first actuator, and the load-sensitive valve group is used to supply oil to the second actuator. The LS port is connected to the second pressure sensor 9. In this embodiment, the first actuator includes a feed motor 5 and a sawing motor 10. The oil inlet of the electro-proportional directional valve group is connected to the P port of the main valve 4. The upper A port and the upper B port are respectively connected to the oil inlet and outlet of the feed motor 5, and the lower A port and the lower B port are respectively connected to the oil inlet and outlet of the sawing motor 10. By switching the valve positions of each directional valve in the electro-proportional directional valve group, the electro-proportional directional valve group can supply oil to the feed motor 5 or the sawing motor 10. The second actuator includes a tilting hydraulic cylinder 6 and a rotary motor 7. The load-sensitive valve group includes a first working link connected to the tilting hydraulic cylinder 6 and a second working link connected to the rotary motor 7. If other actions are added, other actuators 8 can be connected by adding valve plates. The main valve 4 also includes a pressure reducing valve. The pressure oil flowing into the main valve 4 through the P port is reduced in pressure by the pressure reducing valve and can provide pressure oil to the pilot proportional solenoid valves of the left electro-proportional directional valve group and the right load-sensitive valve group. It should be noted that the first actuator (e.g., the feed motor 5 and the sawing motor 10) requires a large flow rate and high control precision, while the second actuator (e.g., the tilting hydraulic cylinder 6 and the rotary motor 7) mainly needs to maintain pressure and does not require high flow control precision. Therefore, this embodiment adopts different control strategies for the first and second actuators.

[0028] like Figure 3 As shown, the working principle of the hydraulic system in this embodiment is explained using the feeding motor 5 and the sawing motor 10 as the first actuators, and the tilting hydraulic cylinder 6 and the rotary motor 7 as the second actuators: When neither the first nor the second actuator is activated, all pilot proportional solenoid valves of the main valve 4 are de-energized, the pressures of the upper and lower variable cylinders of the hydraulic pump 1 are equal, and the hydraulic pump 1 is in a small displacement state under the action of the spring force; pressure sensor 3 and pressure sensor 9 are both in standby pressure. When the feeding motor 5 or the sawing motor 10 needs to operate, the first control strategy is executed. The controller controls the pilot proportional solenoid valve associated with the feeding motor 5 or the sawing motor 10 to be energized according to the input action signal. The control current of the electro-proportional control valve 12 is determined according to the feedback current of the pilot proportional solenoid valve so that the output flow of the hydraulic pump 1 can meet the action requirements of the feeding motor 5 or the sawing motor 10. At the same time, the electro-proportional relief valve of the pressure control valve group 2 is energized, and the load-sensitive control valve 11 is in the right position. At this time, the pilot oil in the lower variable cylinder can return through the load-sensitive control valve 11 and the electro-proportional control valve 12 to adjust the output displacement of the hydraulic pump 1. The displacement of the hydraulic pump 1 is proportional to the control current of the electro-proportional control valve 12. By controlling the control current of the electro-proportional control valve 12 (corresponding to the valve core opening), the output displacement of the hydraulic pump 1 can be proportionally adjusted, thereby accurately controlling the output flow of the hydraulic pump 1, and thus controlling the speed of the feeding motor 5 or the sawing motor 10. Precise control of timber length is achieved through high-speed feeding of the feeding motor 5 and rapid braking after approaching the target length; the control principle of the sawing motor 10 is the same as that of the feeding motor 5; both the feeding motor 5 and the sawing motor 10 integrate speed sensors to collect motor speed; when the speed of the feeding motor 5 or the sawing motor 10 is detected to be too high, the control current of the electro-proportional control valve 12 is reduced to reduce the output displacement of the hydraulic pump 1, which is simple and convenient to control.

[0029] When the tilting hydraulic cylinder 6, the slewing motor 7, or other actuators 8 require individual or combined actions, the second control strategy is executed. The controller controls the pilot proportional solenoid valve associated with the load-sensitive valve group and the tilting hydraulic cylinder 6, the slewing motor 7, or other actuators 8 to be energized according to the input action signal. The LS pressure of the main valve 4 is the pressure collected at the working end by the second pressure sensor 9. According to the pressure collected by the second pressure sensor 9, the controller controls the control current of the proportional relief valve of the pressure control valve group 2 and the electro-proportional control valve 12 of the variable control valve group, so that the outlet pressure of the hydraulic pump 1, i.e. the pressure of the first pressure sensor 3 (the outlet pressure of the hydraulic pump 1), is higher than the second pressure sensor 9 (the LS port pressure of the main valve 4) and maintains a fixed value ΔP. Maintaining ΔP can achieve precise control of the speed of each action, which is not affected by the load pressure.

[0030] If the feeding motor 5 needs to perform a combined action with the tilting hydraulic cylinder 6 or other actuators, the control current of the electro-proportional control valve 12 is first determined according to the first strategy, and then the control current of the electro-proportional control valve is increased based on the control current of the electro-proportional control valve determined by the first strategy to keep the pressure difference detected by the first pressure sensor 3 and the second pressure sensor 9 at the set value.

[0031] This invention employs a hydraulic system consisting of an electronically controlled displacement load-sensitive hydraulic pump and a combined main valve to control the harvesting head. Based on the signals from various action execution signals and pressure sensors, the control current of the electro-proportional relief valve and the electro-proportional control valve is controlled to meet the requirements of action execution. In this embodiment, the load-sensitive feedback pipeline is eliminated, enabling rapid control over long distances.

[0032] In summary, the hydraulic system of this embodiment achieves matching between hydraulic pump 1 and main valve 4, so that the output of hydraulic pump 1 just meets the requirements of action execution, thereby improving accuracy and saving energy and reducing emissions.

[0033] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A hydraulic system for a logging machine's harvesting head, characterized in that, include: Hydraulic pump, with its outlet connected to the first pressure sensor; The pressure control valve assembly has its P port connected to the oil outlet of the hydraulic pump, and its P port is connected in parallel to the LS port of the electro-proportional relief valve and the pressure control valve assembly. The main valve has its P port connected to the outlet of the hydraulic pump, and its P port is connected in parallel to the electro-proportional directional valve group and the load-sensitive valve group. Its LS port is connected to the second pressure sensor. The electro-proportional directional valve group is used to supply oil to the first actuator, and the load-sensitive valve group is used to supply oil to the second actuator. The variable control valve assembly includes a load-sensitive control valve and an electro-proportional control valve located on the control oil circuit of the variable control mechanism of the hydraulic pump. The left end of the load-sensitive control valve is connected to the oil outlet of the hydraulic pump, and the right end is connected to the LS port of the pressure control valve assembly. The output flow rate of the hydraulic pump can be controlled by controlling the valve core position of the load-sensitive control valve and the electro-proportional control valve. The controller is communicatively connected to the first pressure sensor, the electro-proportional relief valve, the electro-proportional control valve, the electro-proportional directional valve group, the load-sensitive valve group, and the second pressure sensor. The variable displacement control mechanism of the hydraulic pump includes an upper variable cylinder and a lower variable cylinder. When oil enters the upper variable cylinder and oil returns from the lower variable cylinder, the displacement of the hydraulic pump increases. The upper port of the load-sensitive control valve is connected to the lower variable cylinder, the first lower port is connected to the outlet of the hydraulic pump, and the second lower port is connected to the upper port of the electro-proportional control valve. The left and right ends of the load-sensitive control valve are respectively connected to the outlet of the hydraulic pump and the LS port of the pressure control valve group. The oil port pressure of the LS port of the pressure control valve group can be controlled by controlling the control current of the electro-proportional relief valve. The load-sensitive control valve includes a left position and a right position; when the load-sensitive control valve is in the left position, the first lower oil port of the load-sensitive control valve is unidirectionally connected to the upper oil port, and the second lower oil port is closed; when the load-sensitive control valve is in the right position, the second lower oil port of the load-sensitive control valve is bidirectionally connected to the upper oil port; the valve core position of the load-sensitive control valve is determined by the pressure of the hydraulic pump outlet and the LS port of the pressure control valve group.

2. The hydraulic system of the logging machine harvesting head according to claim 1, characterized in that, The first lower port of the electro-proportional control valve is connected to the outlet port of the hydraulic pump, and the second lower port is connected to the return port on the hydraulic pump housing. The electro-proportional control valve has a left position and a right position. When the electro-proportional control valve is in the left position, the first lower port is closed, and the second lower port and the upper port are bidirectionally connected. When the electro-proportional control valve is in the right position, the first lower port and the upper port are unidirectionally connected. The valve core position of the electro-proportional control valve can be adjusted by controlling the control current of the electro-proportional control valve. When the load-sensitive control valve is in the right position, the output displacement of the hydraulic pump can be proportionally adjusted by controlling the control current of the electro-proportional control valve.

3. The hydraulic system of the logging machine harvesting head according to claim 1, characterized in that, The pressure control valve assembly also includes: The throttling orifice is located between the P port of the pressure control valve assembly and the oil inlet of the electro-proportional relief valve.

4. The hydraulic system of the logging machine harvesting head according to claim 1, characterized in that, The pressure control valve assembly also includes: The safety valve is connected to the P port of the pressure control valve assembly. The oil outlets of both the safety valve and the electro-proportional relief valve are connected to the hydraulic oil tank through the T port of the pressure control valve assembly.

5. The hydraulic system of the logging machine harvesting head according to claim 1, characterized in that, The first actuator includes a feeding motor and a sawing motor; The inlet of the electro-proportional directional valve assembly is connected to the P port of the main valve, the upper A port and the upper B port are connected to the inlet and outlet ports of the feed motor, respectively, and the lower A port and the lower B port are connected to the inlet and outlet ports of the sawing motor, respectively. By switching the valve positions of each directional valve in the electro-proportional directional valve assembly, the electro-proportional directional valve assembly can supply oil to the feed motor or the sawing motor.

6. The hydraulic system of the logging machine harvesting head according to claim 1, characterized in that, The second actuator includes a tilting hydraulic cylinder and a rotary motor; the load-sensitive valve group includes a first working link connected to the tilting hydraulic cylinder and a second working link connected to the rotary motor.

7. The hydraulic system of the logging machine harvesting head according to claim 1, characterized in that, The main valve also includes: The pressure reducing valve has its inlet connected to the P port of the main valve and its outlet connected to the control terminal of the pilot proportional solenoid valve of the electro-proportional directional valve group and the load-sensitive valve group.

8. A control method for the hydraulic system of a logging machine harvesting head, characterized in that, Based on the hydraulic system of the logging head of any one of claims 1-7, the control method includes: When neither the first nor the second actuator is activated, the hydraulic pump operates in a preset low-pressure, low-displacement state; both the first and second pressure sensors are in standby pressure. When the first actuator needs to operate, the first control strategy is executed. The first control strategy includes: the controller controls the pilot proportional solenoid valve associated with the first actuator to be energized according to the input action signal; the controller determines the control current of the electro-proportional control valve according to the feedback current of the pilot proportional solenoid valve; at the same time, the controller controls the electro-proportional relief valve of the pressure control valve group to be energized, the load-sensitive control valve is in the right position, and the displacement of the hydraulic pump is proportional to the control current of the electro-proportional control valve. When the second actuator needs to operate, the second control strategy is executed. The second control strategy includes: the controller controls the pilot proportional solenoid valve associated with the load-sensitive valve group and the second actuator to be energized according to the input action signal; the controller controls the control current of the electro-proportional control valve and the electro-proportional relief valve with the pressure difference detected by the first pressure sensor and the second pressure sensor being kept at a set value as the target. When the first actuator and the second actuator need to perform a combined action, the control current of the electro-proportional control valve is first determined according to the first control strategy, and then the current is increased based on the control current of the electro-proportional control valve determined by the first control strategy so that the pressure difference detected by the first pressure sensor and the second pressure sensor is maintained at the set value.

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