Load sensing hydraulic system, warming-up control method and working machine

Abstract

The application constructs a load-sensitive hydraulic system, a warming control method and an engineering machine, wherein the hydraulic system comprises a controller, a heating valve group and a temperature detector for detecting the temperature of hydraulic oil; the heating valve group comprises an unloading valve and an electric proportional valve for controlling the opening degree of the valve port of the unloading valve; the oil inlet and outlet ports of the unloading valve are communicated with the EF port of a priority valve and an oil tank circuit; the oil inlet port of the electric proportional valve is connected with a pilot oil source; the first overflow valve arranged between the LS control cavity of the priority valve and the oil tank circuit is an electric proportional overflow valve; the controller is used for controlling the output pressure of the electric proportional valve to make the unloading valve open and controlling the overflow opening pressure of the first overflow valve to be lower than the overflow opening pressure of the second overflow valve in the oil charging pressure output oil circuit of the oil charging valve during the warming process. In the application, the pump displacement and the unloading pressure are gradually increased with the improvement of the oil viscosity during the warming process, and the pump damage caused by high pressure or large flow unloading under the condition of large oil viscosity is avoided.

Description

Technical Field

[0001] This invention relates to a hydraulic system, and more specifically, to a load-sensitive hydraulic system, a warm-up control method, and engineering machinery. Background Technology

[0002] When construction machinery is in operation, its hydraulic system needs to be maintained at a suitable temperature so that the hydraulic fluid has a viscosity suitable for flow in the pipeline. When the construction machinery is first started, the hydraulic fluid in its system is close to the ambient temperature, requiring a warm-up operation for a corresponding period of time based on the hydraulic fluid temperature, so that the hydraulic fluid temperature reaches the requirements for normal operation of the hydraulic system.

[0003] Current methods for warming up construction machinery typically include: installing heating rods in the hydraulic oil tank, using the cooling system of the construction machinery's power system for intervention, or using the hydraulic system's own oil heating to raise the oil temperature. In the aforementioned warm-up methods, using heating rods to heat the hydraulic oil can easily lead to localized high temperatures near the heating rods, causing oil deterioration. While using a cooling system to raise the oil temperature is feasible, in lower temperature areas, the power system itself requires a considerable amount of time to reach its full temperature. For some high-efficiency machines, such as electric machinery, the heat generated during non-operational states is minimal. Using the hydraulic system's own heat generation to raise the hydraulic oil temperature occurs after the machine is started but before any operation is performed. The hydraulic pump outputs oil that flows back to the hydraulic tank through pipelines in the hydraulic system. The amount of heat generated by the hydraulic system's own heat generation depends on the power absorbed by the hydraulic pump from the power supply device (engine or electric motor). For load-sensitive hydraulic systems, the hydraulic pump is a piston pump, which absorbs power from the power device according to the load. When no hydraulic actuators are operated, the variable displacement pump is at its minimum displacement, supplementing the hydraulic system with flow. At this time, the heat generated by the hydraulic oil is very small. Warming up using this method takes a long time, especially in low-temperature (-25℃ to 0℃) and ultra-low-temperature (-50℃ to -25℃) regions. Summary of the Invention

[0004] The technical problem to be solved by the present invention is the warm-up problem of existing load-sensitive hydraulic systems, and provides a load-sensitive hydraulic system, a warm-up control method and engineering machinery, so as to achieve rapid increase of hydraulic system oil temperature.

[0005] The technical solution of this invention to achieve its objective is as follows: a load-sensitive hydraulic system is provided, including a braking hydraulic system, a steering hydraulic system, and a working hydraulic system;

[0006] In the steering hydraulic system, the steering variable pump is connected to the inlet of the priority valve, the EF port of the priority valve is connected to the distribution valve in the working hydraulic system, and the CF port of the priority valve is connected to the inlet of the filling valve in the steering control main valve and the braking hydraulic system; the filling pressure feedback port of the filling valve is connected to the load feedback input terminal of the steering variable pump via a one-way oil circuit.

[0007] Load-sensitive hydraulic systems also include controllers and:

[0008] The heating valve assembly includes an unloading valve and an electro-proportional valve for controlling the opening degree of the unloading valve; the oil inlet and outlet of the unloading valve are connected to the EF port of the priority valve and the oil tank circuit respectively; the oil inlet of the electro-proportional valve is connected to the pilot oil source.

[0009] Temperature detector, used to detect hydraulic oil temperature;

[0010] The first relief valve used to control the maximum pressure in the LS control chamber of the priority valve is an electro-proportional relief valve.

[0011] The controller is used to control the output pressure of the electro-proportional valve during warm-up to open the unloading valve and to control the overflow opening pressure of the first overflow valve to be lower than the overflow opening pressure of the second overflow valve in the filling pressure output oil circuit of the filling valve.

[0012] In the load-sensitive hydraulic system of the present invention, the filling pressure output oil circuit includes a check valve, a reversing valve, a first damping orifice, and a second relief valve; the hydraulic control end of the second relief valve is connected to the oil outlet end of the check valve, the oil inlet end of the second relief valve and the hydraulic control end of the reversing valve are connected to the hydraulic control end of the second relief valve through the first damping orifice, the oil outlet end of the second relief valve and the oil return end of the reversing valve are both connected to the oil return port of the filling valve; the oil inlet end of the check valve and the oil inlet end of the reversing valve are both connected to the oil inlet port of the filling valve; the oil outlet end of the reversing valve is connected to the check oil circuit; the oil outlet end of the reversing valve is selectively connected to the oil inlet end or the oil return end of the second relief valve.

[0013] In the load-sensitive hydraulic system of the present invention, the unidirectional oil circuit includes a first shuttle valve and a second shuttle valve. The oil outlet of the directional valve is connected to the first oil inlet of the first shuttle valve, the second oil inlet of the first shuttle valve is connected to the load feedback port of the steering control master valve, the oil outlet of the first shuttle valve is connected to the first oil inlet of the second shuttle valve, the second oil inlet of the second shuttle valve is connected to the load feedback port of the distribution valve, and the oil outlet of the second shuttle valve is connected to the load feedback input of the steering variable pump. The LS control chamber of the priority valve is connected to the oil outlet of the first shuttle valve via a second damping orifice.

[0014] In the load-sensitive hydraulic system of the present invention, the one-way oil circuit further includes a third damping orifice, and the oil outlet of the first shuttle valve is connected to the second damping orifice and the first oil inlet of the second shuttle valve through the third damping orifice.

[0015] In the load-sensitive hydraulic system of the present invention, the gear pump in the working hydraulic system is connected to the oil inlet of the distribution valve.

[0016] The technical solution of this invention to achieve its objective is as follows: A warm-up control method is provided, applied to the aforementioned load-sensitive hydraulic system, comprising the following steps:

[0017] S1: The controller de-energizes the first relief valve, outputs the maximum current to the electro-proportional valve to make the valve opening of the unloading valve reach the maximum, and executes step S2 after a period of time.

[0018] S2: The controller controls the first relief valve to make its relief opening pressure lower than the relief opening pressure of the relief valve in the filling valve output oil circuit, and outputs the maximum current to the electro-proportional valve to make the valve opening of the unloading valve reach the maximum. After a period of time, step S3 is executed.

[0019] S3: The controller controls the first relief valve to make its relief opening pressure lower than the relief opening pressure of the relief valve in the filling pressure output oil circuit of the filling valve, and outputs a predetermined current to the electro-proportional valve to reduce the valve opening of the unloading valve until the hydraulic oil temperature reaches the predetermined value, at which point the controller cuts off the power to the first relief valve and the electro-proportional valve.

[0020] In the warm-up control method of the present invention, step S2 is executed after the first predetermined time in step S1 or when the hydraulic oil reaches the first predetermined temperature, and step S3 is executed after the second predetermined time in step S2 or when the hydraulic oil reaches the second predetermined temperature.

[0021] In the warm-up control method of the present invention, in the load-sensitive hydraulic system, the second relief valve in the filling pressure output oil circuit is an electro-proportional relief valve; in steps S2 and S3, when the relief opening pressure of the first relief valve reaches its maximum, the controller sends a control current to the second relief valve to increase its maximum relief opening pressure.

[0022] In the warm-up control method of the present invention, in step S3, the controller controls the overflow opening pressure of the first overflow valve to gradually increase according to the time gradient or the hydraulic oil temperature gradient.

[0023] In the warm-up control method of the present invention, in step S3, the control current output by the controller to the electro-proportional valve gradually decreases from the maximum current to a predetermined current according to the time gradient or temperature gradient.

[0024] The technical solution of this invention to achieve its objective is as follows: An engineering machine is provided, which has the aforementioned load-sensitive hydraulic system. The engineering machine can be a loader or a grader.

[0025] Compared with the prior art, in this invention, as the oil viscosity improves during the warm-up process, the pump displacement and unloading pressure are gradually increased, avoiding pump damage caused by high pressure or high flow rate unloading when the oil viscosity is high. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the load-sensitive hydraulic system of the present invention.

[0027] Figure 2 This is a schematic diagram of the warm-up control oil circuit in the load-sensitive hydraulic system of the present invention.

[0028] Component names and serial numbers in the diagram:

[0029] Hydraulic oil tank 1, steering variable pump 2.

[0030] 3. Filling valve, 31. Reversing valve, 32. Second overflow valve, 33. Check valve, 34. First damping orifice, 35. Fourth damping orifice, 36. First shuttle valve, 37. Third damping orifice.

[0031] Flow amplification valve 4, directional control main valve 41, priority valve 42, first relief valve 43, second damping orifice 44

[0032] Heating valve assembly 5, unloading valve 51, electro-proportional valve 52.

[0033] Second shuttle valve 6, parking brake control valve 7, parking brake 8, service brake valve 9, service brake 10, steering gear 11, steering cylinder 12, working pump 13, distribution valve 14, bucket cylinder 15, boom cylinder 16, auxiliary device hydraulic actuator 17, temperature detector 18. Detailed Implementation

[0034] The specific implementation plan is described below with reference to the attached diagram.

[0035] Example 1.

[0036] Figure 1 A load-sensitive hydraulic system for use on a loader is shown, which includes a braking hydraulic system, a steering hydraulic system, and a working hydraulic system.

[0037] like Figure 2As shown, the steering hydraulic system includes a steering variable pump 2, a flow amplification valve 4, a steering gear 11, and a steering cylinder 12. The flow amplification valve 4 includes a priority valve 42, a steering control main valve 41, and a first relief valve 43. The steering gear 11 controls the steering control main valve 41, which controls the steering cylinder 12. The inlet of the priority valve 42 is connected to the pump port of the steering variable pump 2, and the CF port of the priority valve 42 is connected to the inlet of the steering control main valve 41. It is also connected to the filling valve 3 of the brake hydraulic system for supplying oil to the brake hydraulic system. The EF port of the priority valve 42 is connected to the distribution valve 14 in the working hydraulic system for supplying oil to the working hydraulic system. The LS control chamber of the priority valve 42 is connected to the oil tank circuit via the first relief valve 43, and the oil tank circuit is connected to the hydraulic oil tank 1.

[0038] In the heating valve assembly 5, the inlet of the unloading valve 51 is connected to the EF port of the priority valve 42, and the outlet of the unloading valve 51 is connected to the oil tank circuit. The inlet of the electro-proportional valve 52 is connected to the pilot oil source, and the outlet is connected to the hydraulic control end of the unloading valve 51. In this embodiment, the inlet of the electro-proportional valve 52 is connected to the XDP port of the distribution valve 14, and pilot pressure oil is obtained from the pilot pressure oil circuit in the distribution valve 14. In other embodiments, the inlet of the electro-proportional valve 52 can also be connected to a pilot pump or a pilot supply valve.

[0039] like Figure 1 As shown, the working hydraulic system includes a working pump 13, a distribution valve 14 connected to the pump port of the working pump 13, and multiple hydraulic actuators controlled by the distribution valve 14. In the loader, the hydraulic actuators include a bucket cylinder 15, a boom cylinder 16, and auxiliary device hydraulic actuators 17. The pump port of the working pump 13 is connected to the oil inlet of the distribution valve 14. It can be a fixed displacement pump, such as a gear pump, or a variable displacement pump. When the working pump 13 is a variable displacement pump, its load feedback input terminal X1 obtains load pressure information from the load feedback port of the distribution valve 14 so that the working pump can adjust its flow rate according to the load conditions.

[0040] like Figure 1 As shown, the brake hydraulic system includes a filling valve 3, a service brake valve 9 connected to the filling valve 3, a service brake 10 controlled by the service brake valve 9, a parking brake control valve 7 connected to the filling valve 3, a parking brake 8 controlled by the parking brake control valve 7, and an accumulator connected to the filling valve 3. The oil inlet of the filling valve 3 is connected to the CF port of the priority valve 42. When the accumulator pressure is lower than the set value, the filling valve 3 fills the accumulator with liquid to store energy. During the filling process, the filling pressure output oil circuit outputs a filling pressure signal.

[0041] like Figure 2As shown, the filling pressure output oil circuit includes a check valve 33, a reversing valve 31, a first damping orifice 34, and a second relief valve 32. The hydraulic control end of the second relief valve 32 is connected to the oil outlet end of the check valve 33. The oil inlet end of the second relief valve 32 and the hydraulic control end of the reversing valve 31 are connected to the hydraulic control end of the second relief valve 32 through the first damping orifice 34. The oil outlet end of the second relief valve 32 and the oil return end of the reversing valve 31 are both connected to the oil return port of the filling valve 3. The oil inlet end of the check valve 33 and the oil inlet end of the reversing valve 31 are both connected to the oil inlet P of the filling valve 3. The oil outlet end of the reversing valve 31 is connected to the one-way oil circuit. The oil outlet end K of the reversing valve 31 is selectively connected to either the oil inlet end J or the oil return end L. In some embodiments, the oil inlet P of the filling valve 3 is connected to both the oil inlet of the check valve 33 and the oil inlet of the reversing valve 31 via the fourth damping hole 35.

[0042] When the pressure at the outlet of the check valve 33 is lower than the overflow opening pressure of the second relief valve 32, the pressure oil is transmitted through the first damping orifice 34 to the upper end of the directional valve 31. The directional valve 31 is in the upper position, and the oil inlet J and outlet K of the directional valve 31 are connected. The directional valve 31 outputs a filling pressure signal. When the pressure at the outlet of the check valve 33 is higher than the overflow opening pressure of the second relief valve 32, the second relief valve 32 overflows and opens. The upper end of the directional valve 31 is depressurized by the second relief valve 32 and is in the lower position. The oil outlet K and return L of the directional valve 31 are connected, and the directional valve 31 does not output a filling pressure signal.

[0043] like Figure 2 As shown, the unidirectional oil circuit includes a first shuttle valve 36 and a second shuttle valve 6. The oil outlet K of the directional valve 31 is connected to the first oil inlet of the first shuttle valve 36. The second oil inlet of the first shuttle valve 36 is connected to the load feedback port of the steering control master valve 41. The oil outlet of the first shuttle valve 36 is connected to the first oil inlet of the second shuttle valve 6. The second oil inlet of the second shuttle valve 6 is connected to the load feedback port of the distribution valve 14. The oil outlet of the second shuttle valve 6 is connected to the load feedback input X1 of the steering variable pump 2. The LS control chamber of the priority valve 42 is connected to the oil outlet of the first shuttle valve 36 via the second damping orifice 44. Optionally, the unidirectional oil circuit also includes a third damping orifice 37, through which the oil outlet of the first shuttle valve 36 is simultaneously connected to the second damping orifice 44 and the first oil inlet of the second shuttle valve 6. The first shuttle valve 36 compares the pressure signal from the reversing valve 31 with the load pressure signal from the steering control main valve 41 and outputs the signal. The second shuttle valve 6 compares the pressure signal output from the oil outlet of the first shuttle valve with the load pressure signal from the distribution valve and outputs the signal from its oil outlet. The steering variable pump 2 outputs the corresponding flow rate according to the pressure at the oil outlet of the second shuttle valve 6.

[0044] Temperature detector 18 is used to detect the temperature of the hydraulic oil in the hydraulic oil tank. The temperature detector, electro-proportional valve, and controller are electrically connected.

[0045] Example 2.

[0046] This embodiment provides a load-sensitive hydraulic system. Compared with the aforementioned embodiment one, the first relief valve 43 is an electro-proportional relief valve, and the second relief valve 32 is a relief valve with a fixed relief opening pressure. The first relief valve 43 has the maximum relief opening pressure when it is de-energized, and the relief opening pressure of the first relief valve 43 can be adjusted by adjusting the magnitude of its control current.

[0047] The overflow opening pressure of the first relief valve 43 when de-energized is higher than that when energized. When the first relief valve 43 is energized, its overflow opening pressure decreases and it becomes conductive, causing the combined force of the pressure in the LS control chamber of the priority valve 42 and the spring force to be less than the pressure in the opposing chamber of the LS control chamber. The priority valve 42 operates in the left position (oil outlet at port EF), and the pressurized oil input from the inlet of the priority valve 42 flows out from both the CF and EF ports. When the first relief valve 43 is de-energized, causing the combined force of the pressure in the LS control chamber and the spring force to be greater than the pressure in the opposing chamber, the priority valve 42 operates in the right position, and the pressurized oil input from the inlet of the priority valve 42 flows out from the CF port.

[0048] When the hydraulic oil temperature is low and a warm-up operation is required to raise the hydraulic oil temperature, the controller controls the output pressure of the electro-proportional valve 52 and controls the overflow opening pressure of the first relief valve 43 to be lower than the overflow opening pressure of the second relief valve 32. The output pressure of the electro-proportional valve 52 acts on the hydraulic control end of the unloading valve 51, putting it in the open state. The overflow opening pressure of the first relief valve 43 is lower than the overflow opening pressure of the second relief valve 32 in the filling valve 3. In the filling valve 3, the second relief valve 32 is in the closed state, the directional valve 31 works in the upper position, its oil outlet K is connected to the oil inlet J, and the filling pressure output oil circuit outputs the filling pressure signal (the pressure at the oil inlet of the filling valve). The pressure oil output by the directional variable pump 2 flows from the heating valve group 5 to the hydraulic oil tank through the EF port of the priority valve 42. The pressure oil is unloaded and heated by the unloading valve 51, so that the temperature of the pressure oil gradually increases, thus achieving the purpose of warming up.

[0049] Example 3.

[0050] This embodiment provides a load-sensitive hydraulic system. Compared with the aforementioned embodiment two, in this embodiment, the second relief valve 32 is an electro-proportional relief valve. By outputting a corresponding control current to the second relief valve 32, the relief opening pressure of the second relief valve 32 can be increased accordingly.

[0051] When the accumulator is fully charged (its pressure reaches the system pressure), if the second relief valve 32 is de-energized, the pressure at the outlet of the check valve 33 is higher than the overflow opening pressure of the second relief valve 32, causing the second relief valve 32 to open. The directional valve 31 is in the lower position, and the charging pressure output oil circuit does not output a pressure signal. When the accumulator is fully charged (its pressure reaches the system pressure), if the second relief valve 32 is energized, its overflow opening pressure increases. The pressure at the outlet of the check valve 33 is lower than the overflow opening pressure of the second relief valve 32, causing the second relief valve 32 to stop overflowing. The directional valve 31 is in the upper position, and the charging pressure output oil circuit outputs a charging pressure signal (the pressure at the inlet of the charging valve).

[0052] In this embodiment, as in Embodiment 2, the hydraulic oil temperature can be increased to achieve warm-up by controlling the electro-proportional valve 52 and the first relief valve 43, and unloading the unloading valve 51. During the warm-up process, after the first relief valve 43 is de-energized, the second relief valve 32 can be energized to make its overflow opening pressure greater than the opening pressure of the first relief valve 43 in the de-energized state. In this state, the second relief valve 32 is in the overflow cut-off state, and the reversing valve 31 outputs a filling pressure signal (the pressure at the inlet of the output filling valve), causing the variable displacement pump 2 to output higher pressure oil. The unloading valve 51 unloads under the higher pressure state, achieving rapid warm-up operation.

[0053] Example 4.

[0054] This embodiment discloses a warm-up control method, which is applied to the load-sensitive hydraulic system in Embodiment 2. The warm-up control steps are as follows:

[0055] Step S1: The controller de-energizes the first relief valve 43, outputting maximum current to the electro-proportional valve 52. The electro-proportional valve 52 outputs pressurized oil, causing the valve opening of the unloading valve 51 to reach its maximum. This state continues for a first predetermined time (e.g., 1-2 minutes) or until the hydraulic oil temperature reaches a first predetermined temperature (e.g., 2 degrees Celsius). Then, step S2 is executed. During the execution of step S1, the unloading valve 51 is in a large flow state. The displacement of the steering variable pump 2 increases from the standby state until the pressure drop generated by the oil flow reaches the standby pressure of the steering variable pump 2.

[0056] When the first relief valve 43 is de-energized, it operates at its normal overflow opening pressure. When the accumulator is full of oil, the second relief valve 32 is in the overflow opening state, and the reversing valve 31 in the filling valve 3 is in the lower position, not outputting a filling pressure signal.

[0057] Step S2: The controller controls the first relief valve 43 to be energized, and outputs the maximum current to the electro-proportional valve 52 so that the valve opening of the unloading valve 51 reaches the maximum. After this state continues for a second predetermined time (e.g., 1-2 minutes) or until the hydraulic oil temperature reaches a second predetermined temperature (e.g., until the hydraulic oil temperature reaches 5 degrees Celsius), step S3 is executed.

[0058] The opening pressure of the first relief valve 43 is lower than the opening pressure of the second relief valve 32, so the second relief valve 32 is in the closed state. The directional valve 31 is in the upper position, outputting a filling pressure signal. The filling pressure signal output by the filling valve 3 is transmitted to the variable displacement pump 2 through the one-way oil circuit. At this time, the variable displacement pump 2 changes from a load-sensitive pump to a constant pressure pump, outputting flow at maximum displacement, and the pump port pressure also increases. The first relief valve 43 is energized, and the priority valve 42 operates in the left position. Pressure oil is output from the EF and CF ports of the priority valve. The oil output through the EF port is unloaded by the unloading valve 51 and flows back to the hydraulic oil tank. In this step, the heating power of the hydraulic system for the oil is further increased compared to the heating power in step S1.

[0059] Step S3: The controller energizes the first relief valve 43, outputting a predetermined current to the electro-proportional valve 52 to reduce the valve opening of the unloading valve until the hydraulic oil temperature reaches the predetermined value. At this point, the controller de-energizes the first relief valve 43 and the electro-proportional valve 52. In this step, reducing the control current of the electro-proportional valve 52 reduces the valve opening of the unloading valve 51, increasing the pump pressure at the inlet of the variable displacement pump 2. This allows the system to be heated in an overflow state, maximizing the heating power of the hydraulic oil to reach its peak, thus enabling the oil temperature to quickly reach the desired value.

[0060] Optionally, in step S3, the control current output by the controller to the electro-proportional valve 52 gradually decreases from the maximum current to a predetermined current according to the time gradient or the hydraulic temperature gradient. That is, when executing step S3, the control current output by the controller to the electro-proportional valve 52 decreases as the duration increases or as the hydraulic oil temperature increases, decreasing from the maximum current value to the predetermined value, and the opening degree of the unloading valve 51 also decreases gradually accordingly.

[0061] In the above-described warm-up control method, during step S3, the control current of the first relief valve 43 can be gradually reduced according to the time gradient or hydraulic temperature gradient, thereby gradually increasing the relief opening pressure of the first relief valve 43. As the relief opening pressure of the first relief valve 43 gradually increases, the pump port pressure of the steering variable pump 2 will also gradually increase, thereby increasing the unloading pressure of the unloading valve 51. The heat generation power of the hydraulic oil unloaded through the unloading valve 51 increases, and the oil temperature rises faster.

[0062] Optionally, when the second relief valve 32 is an electro-proportional relief valve, after the first relief valve 43 is de-energized, the second relief valve 32 can be energized, the overflow opening pressure of the second relief valve 32 increases and it is in the closed state, the reversing valve 31 in the filling valve 3 is in the upper position, and it outputs the filling pressure signal, thereby making the directional variable pump 2 work in the highest pressure state, and the unloading valve unloads at the highest system pressure, realizing the warm-up operation of rapid oil temperature rise.

[0063] Example 5.

[0064] This embodiment discloses an engineering machinery having the load-sensitive hydraulic system described in Embodiment 2 or 3, such as... Figure 1 As shown. The construction machinery can be a wheel loader or other machinery, such as a grader.

Claims

1. A load-sensitive hydraulic system, comprising a braking hydraulic system, a steering hydraulic system, and a working hydraulic system, In the steering hydraulic system, the steering variable pump is connected to the inlet of the priority valve, the EF port of the priority valve is connected to the distribution valve in the working hydraulic system, and the CF port of the priority valve is connected to the inlet of the filling valve in the steering control main valve and the braking hydraulic system; the filling pressure feedback port of the filling valve is connected to the load feedback input terminal of the steering variable pump via a one-way oil circuit. Its features Load-sensitive hydraulic systems also include controllers and: The heating valve assembly includes an unloading valve and an electro-proportional valve for controlling the opening degree of the unloading valve; the inlet and outlet ports of the unloading valve are connected to the EF port of the priority valve and the oil tank circuit respectively; the inlet port of the electro-proportional valve is connected to the pilot oil source. Temperature detector, used to detect hydraulic oil temperature; The first relief valve used to control the maximum pressure in the LS control chamber of the priority valve is an electro-proportional relief valve. The controller is used to control the output pressure of the electro-proportional valve to open the unloading valve during warm-up, and to control the overflow opening pressure of the first overflow valve to be lower than the overflow opening pressure of the second overflow valve in the filling pressure output oil circuit of the filling valve. The filling pressure output oil circuit includes a check valve, a reversing valve, a first damping orifice, and a second overflow valve; the hydraulic control end of the second overflow valve is connected to the oil outlet end of the check valve; the oil inlet end of the second overflow valve and the hydraulic control end of the reversing valve are connected to the hydraulic control end of the second overflow valve via the first damping orifice; the oil outlet end of the second overflow valve and the oil return end of the reversing valve are both connected to the oil return port of the filling valve; the oil inlet end of the check valve and the oil inlet end of the reversing valve are both connected to the oil inlet port of the filling valve; the oil outlet end of the reversing valve is connected to the one-way oil circuit; the oil outlet end of the reversing valve can be selectively connected to either the oil inlet end or the oil return end; The unidirectional oil circuit includes a first shuttle valve and a second shuttle valve. The oil outlet of the reversing valve is connected to the first oil inlet of the first shuttle valve. The second oil inlet of the first shuttle valve is connected to the load feedback port of the steering control master valve. The oil outlet of the first shuttle valve is connected to the first oil inlet of the second shuttle valve. The second oil inlet of the second shuttle valve is connected to the load feedback port of the distribution valve. The oil outlet of the second shuttle valve is connected to the load feedback input of the steering variable pump. The LS control chamber of the priority valve is connected to the oil outlet of the first shuttle valve through a second damping orifice.

2. The load-sensitive hydraulic system according to claim 1, characterized in that, The unidirectional oil circuit also includes a third damping orifice, through which the oil outlet of the first shuttle valve is simultaneously connected to the second damping orifice and the first oil inlet of the second shuttle valve.

3. A warm-up control method, applied to the load-sensitive hydraulic system of claim 1, characterized in that... The steps are as follows: S1: The controller de-energizes the first relief valve, outputs the maximum current to the electro-proportional valve to make the valve opening of the unloading valve reach the maximum, and executes step S2 after a period of time. S2: The controller controls the first relief valve to make its relief opening pressure lower than the filling pressure in the filling valve and the relief opening pressure of the second relief valve in the output oil circuit, and outputs the maximum current to the electro-proportional valve to make the valve opening of the unloading valve reach the maximum. After a period of time, step S3 is executed. S3: The controller controls the first relief valve to make its relief opening pressure lower than the filling pressure in the filling valve and the relief opening pressure of the second relief valve in the output oil circuit. It outputs a predetermined current to the electro-proportional valve to reduce the valve opening of the unloading valve until the hydraulic oil temperature reaches the predetermined value. At this time, the controller cuts off the power to the first relief valve and the electro-proportional valve.

4. The warm-up control method according to claim 3, characterized in that, Step S1 is executed after the first relief valve continues for a first predetermined time or when the first relief valve continues until the hydraulic oil reaches a first predetermined temperature; Step S2 is executed after the first relief valve continues for a second predetermined time or when the first relief valve continues until the hydraulic oil reaches a second predetermined temperature.

5. The warm-up control method according to claim 3, characterized in that, In the load-sensitive hydraulic system, the second relief valve in the filling pressure output oil circuit is an electro-proportional relief valve; in steps S2 and S3, when the relief opening pressure of the first relief valve reaches its maximum, the controller sends a control current to the second relief valve to increase its maximum relief opening pressure.

6. The warm-up control method according to any one of claims 3-5, characterized in that, In step S3, the controller controls the overflow opening pressure of the first overflow valve to gradually increase based on the time gradient or the hydraulic oil temperature gradient.

7. The warm-up control method according to any one of claims 3-5, characterized in that, In step S3, the control current output by the controller to the electro-proportional valve gradually decreases from the maximum current to the predetermined current according to the time gradient or temperature gradient.

8. An engineering machinery, characterized in that, A load-sensitive hydraulic system having any one of claims 1-2.

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