A hydraulic system, a construction vehicle, and a control method for a hydraulic system

Abstract

The application relates to the technical field of vehicles, and particularly discloses a hydraulic system, an engineering vehicle and a control method of the hydraulic system. The hydraulic system comprises a motor, a hydraulic actuator, a hydraulic driving unit and a hydraulic resistance element. The hydraulic actuator is used for supporting a load; the hydraulic driving unit is in driving connection with the motor, wherein the hydraulic driving unit is configured to provide hydraulic fluid to the hydraulic actuator under the driving of the motor, and the hydraulic driving unit is further configured to rotate under the driving of the hydraulic fluid in the hydraulic actuator and drive the motor to generate electricity; the hydraulic resistance element is in hydraulic connection between the hydraulic driving unit and the hydraulic actuator, and the hydraulic resistance element is configured to adjust the pressure difference between the hydraulic actuator and the hydraulic driving unit. Therefore, the motor can be selected to be a motor with a low rated torque, the rated power of a frequency converter can be reduced, the rotational inertia of the motor can be reduced, the dynamic response time of the system during speed change can be reduced, and the system cost can be reduced.

Description

Technical Field

[0001] This invention relates to the field of vehicle technology, and in particular to a hydraulic system, an engineering vehicle, and a control method for the hydraulic system. Background Technology

[0002] Engineering vehicles typically use hydraulic systems to drive actuators, which in turn drive the load. The actuators usually move in either linear extension or rotational motion. For linear extension, the actuator is typically a linear cylinder, driven by a pump; for rotation, the actuator is typically a motor, also driven by a pump. Taking a linear cylinder as an example, as the load is raised, its potential energy increases. As the load falls back down, its potential energy decreases. This reduced potential energy is usually converted into heat energy in the hydraulic fluid, resulting in energy waste.

[0003] In response to this, related technologies incorporate potential energy recovery devices into hydraulic systems. During the load descent process, a pump drives a motor to generate electricity, which is then stored in energy recovery devices such as batteries to recover energy and improve energy utilization. For example, the electro-hydraulic work vehicle with energy recovery function disclosed in the earlier patent application CN201811267079.9 recovers energy in this way. However, during the load descent process, the load typically needs to switch between three motion modes: acceleration, constant speed, and deceleration. During the transition from acceleration to constant speed and during deceleration, the hydraulic oil needs to withstand significant reaction forces, which can reach the system's maximum pressure. This results in a large torque on the pump and an increase in the motor's torque, potentially reaching the motor's maximum torque. Therefore, in related technologies, when selecting a motor, it is usually necessary to select the motor model accordingly so that the motor can withstand the maximum torque during the load reduction process. However, this will result in a large rated torque of the motor, and the rated power of the frequency converter used with the motor will also need to be increased significantly, increasing the system cost. In addition, the increase in the rated torque of the motor will also lead to an increase in the rotational inertia of the motor, which will limit the dynamic response time of the system when the speed changes. Summary of the Invention

[0004] The purpose of this invention is to provide a hydraulic system, an engineering vehicle, and a control method for the hydraulic system, so as to reduce the cost of the hydraulic system.

[0005] In a first aspect, the present invention provides a hydraulic system comprising: Electric motor; Hydraulic actuators are used to support loads; A hydraulic drive unit is connected to the motor, wherein the hydraulic drive unit is configured to provide hydraulic fluid to the hydraulic actuator under the active drive of the motor, and the hydraulic drive unit is further configured to rotate under the drive of the hydraulic fluid in the hydraulic actuator and drive the motor to generate electricity; A hydraulic resistance element is hydraulically connected between the hydraulic drive unit and the hydraulic actuator, and the hydraulic resistance element is configured to adjust the pressure difference between the hydraulic actuator and the hydraulic drive unit.

[0006] As a preferred technical solution for the hydraulic system, the hydraulic actuator is a linear cylinder, and the hydraulic drive unit includes a first fixed displacement hydraulic pump and a second fixed displacement hydraulic pump. The two ends of the first fixed displacement hydraulic pump are respectively connected to the rod chamber and the rodless chamber of the linear cylinder, and the second fixed displacement hydraulic pump is used to compensate for the volume difference between the piston rod chamber and the rodless chamber.

[0007] As a preferred technical solution for the hydraulic system, the hydraulic actuator is a hydraulic motor, and the hydraulic drive unit includes a first fixed displacement hydraulic pump and a second fixed displacement hydraulic pump. The first fixed displacement hydraulic pump and the hydraulic motor form a circulation loop, and the second fixed displacement hydraulic pump is used to replenish oil to the circulation loop.

[0008] As a preferred technical solution for the hydraulic system, the hydraulic system further includes a pressure sensor, which is used to detect the pressure on the side of the hydraulic actuator adjacent to the hydraulic resistance element.

[0009] As a preferred technical solution for the hydraulic system, the hydraulic system further includes a controller, which is electrically connected to the pressure sensor and the hydraulic resistance element respectively, and the controller is configured to control the opening degree of the hydraulic resistance element based on the pressure detected by the pressure sensor.

[0010] As a preferred technical solution for the hydraulic system, the hydraulic system further includes an inverter, which is connected to the controller and the motor, and is used to connect to a battery or electrical appliance.

[0011] As a preferred technical solution for the hydraulic system, the hydraulic drive unit is a proportional control lift valve or a proportional control spool valve.

[0012] The hydraulic system provided by this invention has at least the following beneficial effects: The hydraulic system includes a motor, a hydraulic actuator, a hydraulic drive unit, and a hydraulic resistance element. The hydraulic actuator supports the load; the hydraulic drive unit is connected to the motor and is configured to supply hydraulic fluid to the hydraulic actuator under the active drive of the motor. The hydraulic drive unit is also configured to rotate under the drive of the hydraulic fluid in the hydraulic actuator and drive the motor to generate electricity; the hydraulic resistance element is hydraulically connected between the hydraulic drive unit and the hydraulic actuator, and is configured to regulate the pressure difference between the hydraulic actuator and the hydraulic drive unit. The hydraulic system provided in this embodiment, when the load decreases, the hydraulic actuator outputs hydraulic fluid under the action of the load. The hydraulic fluid drives the hydraulic drive unit to rotate, and the hydraulic drive unit drives the motor to generate electricity. When the load decelerates or changes from accelerating to constant speed, the pressure of the hydraulic fluid output from the hydraulic actuator increases, and the pressure can easily reach the maximum system pressure. At this time, a pressure difference is provided between the hydraulic actuator and the hydraulic drive unit through the hydraulic resistance element, which can reduce the pressure on the hydraulic drive unit. Since pressure is positively correlated with torque, the torque borne by the hydraulic drive unit can be reduced, thereby reducing the torque borne by the motor and preventing the motor torque from exceeding the limit. This means that the rated torque of the motor does not need to match the maximum system pressure. When selecting a motor, a motor with a lower rated torque can be selected, thereby reducing system cost. In addition, the relatively reduced rated torque of the motor can also reduce the rated power of the frequency converter used with the motor, further reducing costs. Furthermore, the relatively reduced rated torque of the motor can also reduce the rotational inertia of the motor, reducing the dynamic response time of the system when the speed changes.

[0013] Secondly, the present invention provides an engineering vehicle comprising a hydraulic system as described in any of the above embodiments, the engineering vehicle further comprising a working device, the working device being throttle-connected to the hydraulic actuator.

[0014] The engineering vehicle provided by this invention has at least the following beneficial effects: The engineering vehicle includes the aforementioned hydraulic system, which can effectively reduce the cost of the engineering vehicle.

[0015] Thirdly, the present invention provides a control method for a hydraulic system, which is implemented using any of the hydraulic systems described above, and the control method includes: The load has begun to decrease; The actual pressure of the hydraulic fluid output by the hydraulic actuator is acquired in real time. Compare the actual pressure with the set pressure; When the actual pressure exceeds the set pressure, the opening degree of the hydraulic resistance element is adjusted based on the actual pressure; wherein, when the hydraulic resistance element is fully open and the load drops, when the actual torque of the motor is equal to the maximum torque allowed by the inverter, the pressure of the hydraulic fluid output by the hydraulic actuator is the set pressure.

[0016] As a preferred technical solution for the control method of a hydraulic system, the hydraulic resistance element remains fully open when the actual pressure does not exceed the set pressure.

[0017] The hydraulic system control method provided by this invention has at least the following beneficial effects: The control method of this hydraulic system includes: after determining that the load has begun to recede, acquiring the actual pressure of the hydraulic fluid output by the hydraulic actuator in real time; comparing the actual pressure with the set pressure; when the actual pressure exceeds the set pressure, adjusting the opening of the hydraulic resistance element based on the actual pressure, so that the hydraulic resistance element can generate a pressure difference between the hydraulic actuator and the hydraulic drive unit, thereby reducing the pressure of the hydraulic drive unit. Since pressure and torque are positively correlated, the torque applied to the hydraulic drive unit and the torque applied to the motor by the hydraulic drive unit can be reduced simultaneously, and the torque borne by the motor does not exceed the maximum torque allowed by the inverter. This allows for the selection of a motor with a lower rated power, thereby reducing system costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the hydraulic system in an embodiment of the present invention; Figure 2 This is a flowchart of the control method of the hydraulic system in an embodiment of the present invention; Figure 3 This is a schematic diagram illustrating the parameter changes of the hydraulic system during the load reduction process in an embodiment of the present invention.

[0019] In the picture: 1. Motor; 2. Hydraulic actuator; 21. Rod chamber; 22. Rodless chamber; 3. Hydraulic drive unit; 31. First constant displacement hydraulic pump; 32. Second constant displacement hydraulic pump; 4. Hydraulic resistance element; 5. Pressure sensor; 6. Controller; 7. Inverter; 8. Oil tank; 9. Load; 10. Valve assembly. Detailed Implementation

[0020] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for 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. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions. Furthermore, "above," "on top of," and "over" the first feature in relation to the second feature includes the first feature directly above and diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "under," and "below" the first feature in relation to the second feature includes the first feature directly below and diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0022] 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 can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0024] In related technologies, potential energy recovery devices are introduced into hydraulic systems. During load descent, a pump drives a motor to generate electricity, which is then stored in batteries or other energy recovery devices to recover energy and improve energy utilization. However, during load descent, the load typically needs to switch between three motion modes: acceleration, constant speed, and deceleration. During the transition from acceleration to constant speed and during deceleration, the hydraulic oil needs to withstand significant reaction forces, sometimes reaching the system's maximum pressure. This results in high torque on the pump and increased motor torque, potentially reaching the motor's maximum torque. Therefore, in related technologies, motor selection typically requires choosing a model that can withstand maximum torque during load descent. However, this results in a very high rated torque for the motor and a significant increase in the rated power of the inverter used with the motor, leading to increased system costs. Furthermore, the increased rated torque also increases the motor's moment of inertia, limiting the system's dynamic response time during speed changes.

[0025] To address this issue, this embodiment provides a hydraulic system that can be applied to engineering vehicles.

[0026] Please refer to Figure 1The hydraulic system includes a motor 1, a hydraulic actuator 2, a hydraulic drive unit 3, and a hydraulic resistance element 4. The hydraulic actuator 2 supports a load 9. The hydraulic drive unit 3 is connected to the motor 1 and is configured to supply hydraulic fluid to the hydraulic actuator 2 under the active drive of the motor 1. The hydraulic drive unit 3 is also configured to rotate under the drive of the hydraulic fluid output from the hydraulic actuator 2 and drive the motor 1 to generate electricity. The hydraulic resistance element 4 is hydraulically connected between the hydraulic drive unit 3 and the hydraulic actuator 2, and is configured to adjust the pressure difference between the hydraulic actuator 2 and the hydraulic drive unit 3. In the hydraulic system provided in this embodiment, when the load 9 falls, the hydraulic actuator 2 outputs hydraulic fluid under the action of the load 9. The hydraulic fluid drives the hydraulic drive unit 3 to rotate, and the hydraulic drive unit 3 drives the motor 1 to generate electricity. When the load 9 decelerates or changes from accelerating to constant speed, the pressure of the hydraulic fluid output from the hydraulic actuator 2 will increase, and the pressure can easily reach the maximum system pressure. At this time, the hydraulic resistance element 4 provides a pressure difference between the hydraulic actuator 2 and the hydraulic drive unit 3, which can reduce the pressure on the hydraulic drive unit 3. Since pressure is positively correlated with torque, the torque borne by the hydraulic drive unit 3 can be reduced, thereby reducing the torque borne by the motor 1 and preventing the motor 1 from exceeding the torque limit set by the inverter 7. Therefore, when selecting and determining the required torque capacity of motor 1, calculations can be performed independently of the maximum pressure of the hydraulic system. This allows for the selection of motor 1 with a lower torque capacity compared to existing technologies, thereby reducing system costs. Furthermore, the relatively lower rated torque of motor 1 also reduces the rated power of the frequency converter used with motor 1, further lowering costs. Additionally, the relatively lower rated torque of motor 1 also reduces the moment of inertia of motor 1, thus reducing the dynamic response time of the system when speed changes.

[0027] Specifically, in this embodiment, when the load 9 needs to be lifted, the motor 1 is in motor mode. The motor 1 can output torque under electric drive to drive the hydraulic drive unit 3 to rotate, thereby causing the hydraulic drive unit 3 to drive hydraulic fluid into the hydraulic actuator 2, so as to lift the load 9. When the load 9 falls back, under the action of gravity of the load 9, the hydraulic actuator 2 outputs hydraulic fluid, which enters the hydraulic drive unit 3, thereby causing the hydraulic drive unit 3 to drive the motor 1 to rotate, so that the motor 1 generates electricity. At this time, the motor 1 is in generator mode.

[0028] It should be noted that in this embodiment, when the fluid pressure output by the hydraulic actuator 2 driven by the load 9 exceeds the pre-charge pressure, the motor 1 switches to generator mode. At this time, under the drive of the load 9, the hydraulic drive unit 3 can drive the motor 1 to rotate and generate electricity; when the load 9 is insufficient to drive the hydraulic drive unit 3, the motor 1 is in electric motor mode.

[0029] In some embodiments, the hydraulic fluid is hydraulic oil. In other embodiments, the hydraulic fluid may be other liquid media as needed, such as water-based hydraulic fluid.

[0030] In this embodiment, the hydraulic system also includes a valve group 10, which is used to regulate the hydraulic system.

[0031] In some embodiments, the valve assembly 10 includes a load holding valve hydraulically connected between the hydraulic drive unit 3 and the hydraulic actuator 2. The load holding valve enables hydraulic fluid to be held in the hydraulic actuator 2 and also enables hydraulic fluid to flow between the hydraulic actuator 2 and the hydraulic drive unit 3.

[0032] In some embodiments, valve assembly 10 further includes a flushing relief valve for allowing the higher pressure side of the hydraulic actuator 2 to overflow into the oil tank 8.

[0033] In some embodiments, the valve assembly 10 further includes a pressure shut-off valve for connecting or disconnecting the hydraulic drive unit 3 and the hydraulic actuator 2.

[0034] In some embodiments, the valve assembly 10 further includes a variable cross-section brake valve connected in series between the hydraulic drive unit 3 and the hydraulic actuator 2.

[0035] In some embodiments, please refer to Figure 1 The hydraulic actuator 2 is a linear cylinder. The hydraulic drive unit 3 includes a first constant displacement hydraulic pump 31 and a second constant displacement hydraulic pump 32. The two ends of the first constant displacement hydraulic pump 31 are connected to the rod chamber 21 and the rodless chamber 22 of the linear cylinder, respectively. The second constant displacement hydraulic pump 32 is connected to the rodless chamber 22 of the linear cylinder. The second constant displacement hydraulic pump 32 is used to compensate for the volume difference between the piston rod chamber 21 and the rodless chamber 22. Specifically, the second constant displacement hydraulic pump 32 is used to supplement hydraulic fluid to the connecting pipeline between the linear cylinder and the rodless chamber 22. The hydraulic resistance element 4 is hydraulically connected between the first constant displacement hydraulic pump 31 and the rodless chamber 22 of the linear cylinder.

[0036] Specifically, in this embodiment, the first fixed displacement hydraulic pump 31 can rotate bidirectionally. When the load 9 is lifted, the motor 1 is in motor mode, driving the first fixed displacement hydraulic pump 31 and the second fixed displacement hydraulic pump 32 to work. The hydraulic resistance element 4 is in fully open mode, that is, the hydraulic resistance element 4 will not generate a pressure difference between the linear cylinder and the first fixed displacement hydraulic pump 31. The first fixed displacement hydraulic pump 31 pumps the hydraulic fluid in the rod chamber 21 of the linear cylinder to the rodless chamber 22 of the linear cylinder, causing the piston rod of the linear cylinder to extend, thereby lifting the load 9 and increasing the kinetic and potential energy of the load 9. When the load 9 falls back, and when the pressure in the rodless chamber 22 is lowered... When the pressure is greater than the pre-charge pressure, under the drive of the load 9, the hydraulic fluid in the rodless chamber 22 of the linear cylinder flows to the first fixed displacement hydraulic pump 31 and drives the first fixed displacement hydraulic pump 31 to rotate. Then, it is delivered to the rod chamber 21 of the linear cylinder through the first fixed displacement hydraulic pump 31. At the same time, the first fixed displacement hydraulic pump 31 drives the motor 1 to rotate and generate electricity. The motor 1 is in generator mode. At this time, the hydraulic resistance element 4 adjusts the opening based on the pressure of the hydraulic fluid on the rodless chamber 22 side, thereby adjusting the pressure difference between the linear cylinder and the first fixed displacement hydraulic pump 31 to avoid overload of the motor 1.

[0037] In addition, due to the difference in cross-sectional area between the rodless chamber 22 and the rod chamber 21, when the load 9 is lifted, the second constant displacement hydraulic pump 32 pumps the hydraulic fluid in the oil tank 8 to the rodless chamber 22 of the linear cylinder; when the load 9 falls back, the excess hydraulic fluid overflows into the oil tank 8 through the flushing relief valve.

[0038] As an alternative, the hydraulic actuator 2 is a hydraulic motor, and the hydraulic drive unit 3 includes a first fixed-displacement hydraulic pump 31 and a second fixed-displacement hydraulic pump 32. The first fixed-displacement hydraulic pump 31 and the hydraulic motor form a circulation loop, and the second fixed-displacement hydraulic pump 32 is used to replenish oil to the circulation loop. A hydraulic resistance element 4 is hydraulically connected between the first fixed-displacement hydraulic pump 31 and the hydraulic motor. Specifically, the first fixed-displacement hydraulic pump 31 can also rotate in both directions. The hydraulic motor can drive rotating devices such as drums to lift the load 9. When the load 9 is lifted, the motor 1 is in motor mode, driving the first fixed-displacement hydraulic pump 31 and the second fixed-displacement hydraulic pump 32. The hydraulic resistance element 4 is in fully open mode, meaning that the hydraulic resistance element 4 does not generate a pressure difference between the hydraulic motor and the first fixed-displacement hydraulic pump 31. The hydraulic fluid is driven by the first fixed-displacement hydraulic pump 31 to circulate between the hydraulic motor and the first fixed-displacement hydraulic pump 31. The hydraulic motor drives rotating mechanisms such as drums to rotate, thereby lifting the load 9. When load 9 falls back, driven by load 9, the hydraulic motor drives the hydraulic fluid to flow between the hydraulic motor and the first fixed displacement hydraulic pump 31. When the pressure of the hydraulic fluid driven by the hydraulic motor exceeds the pre-charge pressure, the first fixed displacement hydraulic pump 31 drives motor 1 to rotate, causing motor 1 to generate electricity. Motor 1 is in generator mode. At this time, the hydraulic resistance element 4 adjusts its opening based on the pressure of the hydraulic fluid on the output side of the hydraulic motor, thereby adjusting the pressure difference between the output side of the hydraulic motor and the input side of the first fixed displacement hydraulic pump 31 to prevent motor 1 from overloaded. In addition, in this hydraulic system, during the lifting and lowering of load 9, the second fixed displacement hydraulic pump 32 replenishes the oil in the circulation loop between the first fixed displacement hydraulic pump 31 and the hydraulic motor.

[0039] In some embodiments, the hydraulic system further includes a pressure sensor 5, which is used to detect the pressure on the side of the hydraulic actuator 2 adjacent to the hydraulic resistance element 4. Specifically, when the hydraulic actuator 2 is a linear cylinder, the pressure sensor 5 is used to detect the pressure of the hydraulic fluid on the rodless chamber 22 side of the linear cylinder; when the hydraulic actuator 2 is a hydraulic motor, and when the load 9 falls, the pressure sensor 5 is used to detect the pressure on the output side of the hydraulic motor.

[0040] In some embodiments, the hydraulic drive unit 3 is a proportional control lift valve or a proportional control spool valve. Both the proportional control lift valve and the proportional control spool valve are existing valve components, and their specific structures will not be described in detail in this embodiment.

[0041] In some embodiments, the hydraulic system further includes a controller 6, which is electrically connected to the pressure sensor 5 and the hydraulic resistance element 4, respectively. The controller 6 is configured to control the opening of the hydraulic resistance element 4 based on the pressure detected by the pressure sensor 5. Thus, when the load 9 drops, the controller 6 controls the hydraulic resistance element 4 to maintain an appropriate opening based on the pressure value detected by the pressure sensor 5, so that the torque acting on the motor 1 remains within the allowable torque range.

[0042] In some embodiments, the hydraulic system further includes an inverter 7, which is connected to the controller 6 and the motor 1. The inverter 7 is used to connect to a battery or electrical appliance. The inverter 7 is used to convert the electricity generated by the motor 1 into alternating current and store it in an energy storage device such as a battery, or to directly supply it to other electrical components on the vehicle.

[0043] This embodiment also provides an engineering vehicle, which includes the aforementioned hydraulic system and a working device connected to the hydraulic actuator 2. The use of this hydraulic system in the engineering vehicle effectively reduces its cost. Examples of engineering vehicles include excavators, loaders, and winches.

[0044] In some embodiments, the working device includes a working arm, and a hydraulic system is used to drive the working arm to swing. Taking an excavator as an example, the working arm can be the boom of the excavator, which needs to be frequently raised and lowered during the operation of the excavator. When the working arm is raised, the motor 1 is in motor mode, and the first fixed displacement hydraulic pump 31 drives hydraulic fluid into the rodless chamber 22 of the linear cylinder, so that the piston rod of the linear cylinder drives the working arm to rise. When the working arm falls, the working arm acts as a load 9. Under the action of the working arm, if the oil pressure in the rodless chamber 22 is greater than the pre-charge pressure, the first fixed displacement hydraulic pump 31 can drive the motor 1 to generate electricity, thereby recovering the potential energy of the working arm.

[0045] In some embodiments, the working device includes a drum, and the hydraulic actuator 2 is used to drive the drum to rotate. Engineering vehicles such as winches and cranes, taking a winch as an example, are equipped with a drum driven by a hydraulic motor. When the load 9 (cargo) is lifted by the drum, the motor 1 is in motor mode, and the first fixed-displacement hydraulic pump 31 actively drives the hydraulic fluid to circulate between the first fixed-displacement hydraulic pump 31 and the hydraulic motor. The hydraulic motor drives the drum to rotate, thus lifting the load 9. When the load 9 falls back, the load 9 drives the hydraulic motor to rotate, thereby causing the hydraulic fluid to circulate between the hydraulic motor and the first fixed-displacement hydraulic pump 31. If the pressure at the output end of the hydraulic motor is greater than the pre-charge pressure, the first fixed-displacement hydraulic pump 31 can drive the motor 1 to generate electricity, thereby recovering the potential energy of the load 9.

[0046] This embodiment also provides a control method for a hydraulic system, which is implemented through the aforementioned hydraulic system.

[0047] Specifically, please refer to Figure 2 The control method for this hydraulic system includes the following steps.

[0048] S100: Confirmed load 9 has begun to decline.

[0049] There are many ways to determine when load 9 begins to fall. For example, when the button controlling the fall of load 9 on the engineering vehicle is pressed, or when the control handle is in the area controlling the fall of load 9, it can be determined that load 9 has begun to fall. In addition, the swing direction of the boom and the rotation direction of the drum can be obtained; when the boom swings downward and the drum rotates in a direction that causes the load to fall downward, it can be determined that load 9 has begun to fall.

[0050] S200: Real-time acquisition of the actual pressure of the hydraulic fluid output by hydraulic actuator 2.

[0051] The actual pressure of the hydraulic fluid output by the hydraulic actuator 2 can be detected by the pressure sensor 5.

[0052] S300: Compares the actual pressure with the set pressure.

[0053] The set pressure can be set according to the actual model of motor 1 and the maximum allowable torque of inverter 7. When hydraulic resistance element 4 is fully open and load 9 is reduced, the hydraulic oil pressure output by hydraulic actuator 2 is defined as the set pressure when the actual torque of motor 1 reaches the rated torque allowed by inverter 7.

[0054] When the actual pressure exceeds the set pressure, execute S400.

[0055] S400: Adjusts the opening degree of hydraulic resistance element 4 based on actual pressure.

[0056] The controller 6 stores the correspondence between the actual pressure and the hydraulic resistance element 4 in advance, and this correspondence can be obtained through a large number of experiments in the early stage.

[0057] When the opening of the hydraulic resistance element 4 is adjusted based on the actual pressure, the hydraulic resistance element 4 can generate a pressure difference between the hydraulic actuator 2 and the hydraulic drive unit 3, thereby reducing the pressure on the hydraulic drive unit 3. Since pressure and torque are positively correlated, the torque applied to the hydraulic drive unit 3 and the torque applied to the motor 1 by the hydraulic drive unit 3 can be reduced simultaneously, and the torque acting on the motor 1 can be kept below the allowable torque limit. This is beneficial for selecting a model with a lower rated power for the motor 1 to reduce system costs.

[0058] In some embodiments, in step S300, when the actual pressure does not exceed the set pressure, step S500 is executed.

[0059] S500: Hydraulic resistance element 4 remains fully open.

[0060] When the actual pressure does not exceed the set pressure, the hydraulic resistance element 4 remains fully open, so that the pressure on the output side of the hydraulic actuator 2 is the same as the pressure on the input side of the hydraulic drive unit 3. However, this pressure ensures that the torque applied to the motor 1 by the hydraulic actuator will not exceed the rated torque, and the motor 1 can work stably.

[0061] In this embodiment, taking the hydraulic actuator 2 as a linear cylinder as an example, when the load 9 falls back and the pressure in the rodless chamber 22 is greater than the pre-charge pressure, during the fall of the load 9, the pressure in the rodless chamber 22 first gradually decreases to the pre-charge pressure and remains constant, and then the pressure in the rodless chamber 22 gradually increases and exceeds the set pressure; and during the process of the pressure in the rodless chamber 22 gradually decreasing to the pre-charge pressure, the pressure in the rod chamber 21 first gradually increases to be equal to the pressure in the rodless chamber 22, and then gradually decreases to the pre-charge pressure and remains constant; before the pressure in the rodless chamber 22 gradually increases and exceeds the set pressure, the acceleration of the load 9 gradually increases to be close to or equal to the acceleration due to gravity and then remains constant; after the pressure in the rodless chamber 22 exceeds the set pressure, the hydraulic resistance element 4 begins to participate in the differential pressure regulation, and the acceleration of the load 9 gradually decreases to zero.

[0062] Specifically, please refer to Figure 3 The control process of a hydraulic system can be divided into stage I, stage II, stage III, stage IV and stage V.

[0063] In stage I, initially, because the hydraulic fluid in the rodless chamber 22 supports the load 9, the actual pressure on the rodless chamber 22 side is determined by the load 9 and is higher than the pre-charge pressure. As the load 9 decreases, the hydraulic fluid in the rodless chamber 22 drives the first constant displacement hydraulic pump 31 to rotate, which in turn drives the motor 1 to rotate, causing the motor 1 to start generating electricity. At the same time, the first constant displacement hydraulic pump 31 delivers hydraulic fluid to the rod chamber 21. Due to the difference in cross-section between the rod chamber 21 and the rodless chamber 22, the pressure of the hydraulic fluid in the rod chamber 21 increases, which causes the load 9 to increase... The load 9 falls rapidly, but as time goes on, in the subsequent stages, the acceleration of the load 9 will gradually stabilize and become equal to or close to the acceleration due to gravity. The load 9 will be in free fall, and the rate of change of volume of the rod chamber 21 and the rodless chamber 22 will gradually become equal. Due to the difference in cross-sectional area between the rod chamber 21 and the rodless chamber 22, the excess oil can be returned to the oil tank in time through overflow, so that the oil pressure in the rod chamber 21 and the rodless chamber 22 will gradually approach the pre-charge pressure. Of course, in some special cases, such as the overflow valve failure, the pressure in the rod chamber 21 may be higher than the pre-charge pressure.

[0064] In stage I, the actual pressure on the rodless chamber 22 side will not exceed the set pressure, thus the hydraulic resistance element 4 is in the fully open state.

[0065] In stage II, the load 9 accelerates back down due to gravity. At this time, the pressure in the rod chamber 21 and the rodless chamber 22 is basically the same, or the pressure on the rod chamber 21 side may be higher than that on the rod chamber 22 side under some special circumstances, and the piston rod of the linear cylinder 2 retracts rapidly.

[0066] In stage II, the pressure on the rodless chamber 22 side will not exceed the set pressure, thus the hydraulic resistance element 4 is in a fully open state. Furthermore, in both stages I and II, because the hydraulic resistance element 4 is in a fully open state, the actual pressure on the rodless chamber 22 side is equal to the pressure on the input side of the first constant displacement hydraulic pump 31.

[0067] In addition, during phases I and II, the amount of hydraulic fluid discharged from the rodless chamber 22 will gradually increase, resulting in a proportional increase in the rotational speed of the first constant displacement hydraulic pump 31.

[0068] In Phase III, the acceleration of the first constant displacement hydraulic pump 31 will slow down. This is due to the limitations imposed by the design parameters of the first constant displacement hydraulic pump 31, preventing it from accelerating indefinitely. This will lead to an increase in pressure on the rodless chamber 22 side. However, in Phase III, the speed of the load 9 can still increase due to gravitational acceleration. This is because the displacement of the first constant displacement hydraulic pump 31 is still sufficient to meet the discharge requirements of the hydraulic fluid in the rodless chamber 22, and will not affect the change in the descent speed of the load 9.

[0069] In stage III, the actual pressure on the rodless chamber 22 side gradually increases to close to the set pressure, that is, the torque borne by motor 1 gradually approaches the allowable torque limit of motor 1, but does not exceed it. Therefore, the hydraulic resistance element 4 is still in the fully open state.

[0070] In stage IV, the pressure on the rodless chamber 22 side continues to rise to a certain level (greater than the weight of load 9) and then gradually decreases, always exceeding the set pressure. At this time, the hydraulic resistance element 4 is activated and its opening is adjusted based on the actual pressure on the rodless chamber 22 side. The hydraulic resistance element 4 applies a pressure difference between the rodless chamber 22 and the first constant displacement hydraulic pump 31, so that the pressure on the input side of the first constant displacement hydraulic pump 31 will not exceed the set pressure and can remain stable, so that the torque of the motor 1 is maintained at a level close to the allowable torque and remains stable, ensuring the normal operation of the motor 1.

[0071] In stage IV and the subsequent stage V, due to inertia, the pressure difference between the rodless chamber 22 and the rod chamber 21 will first exceed the weight of the load 9 and then gradually decrease to below the weight of the load 9, fluctuating back and forth until it is equal to the weight of the load 9, causing the acceleration of the load 9 to gradually approach zero, and the load 9 will fall back at a constant speed. In the early stage of stage V, the pressure on the rodless chamber 22 side may be lower than the set pressure and rise back to above the set pressure. At this time, the opening of the hydraulic resistance element 4 can be controlled according to the actual situation.

[0072] The above description is merely a preferred embodiment of the present invention and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this invention is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this invention.

Claims

1. A hydraulic system, characterized in that, include: Motor (1); Hydraulic actuator (2) is used to support the load (9); A hydraulic drive unit (3) is connected to the motor (1) for transmission. The hydraulic drive unit (3) is configured to provide hydraulic fluid to the hydraulic actuator (2) under the active drive of the motor (1). The hydraulic drive unit (3) is also configured to rotate under the drive of the hydraulic fluid output by the hydraulic actuator (2) and drive the motor (1) to generate electricity. A hydraulic resistance element (4) is hydraulically connected between the hydraulic drive unit (3) and the hydraulic actuator (2), and the hydraulic resistance element (4) is configured to adjust the pressure difference between the hydraulic actuator (2) and the hydraulic drive unit (3).

2. The hydraulic system according to claim 1, characterized in that, The hydraulic actuator (2) is a linear cylinder, and the hydraulic drive unit (3) includes a first fixed displacement hydraulic pump (31) and a second fixed displacement hydraulic pump (32). The two ends of the first fixed displacement hydraulic pump (31) are respectively connected to the rod chamber (21) of the linear cylinder and the rodless chamber (22) of the linear cylinder. The first fixed displacement hydraulic pump (32) is used to compensate for the volume difference between the piston rod chamber (21) and the rodless chamber (22).

3. The hydraulic system according to claim 1, characterized in that, The hydraulic actuator (2) is a hydraulic motor, and the hydraulic drive unit (3) includes a first fixed displacement hydraulic pump (31) and a second fixed displacement hydraulic pump (32). The first fixed displacement hydraulic pump (31) and the hydraulic motor form a circulation loop, and the second fixed displacement hydraulic pump (32) is used to replenish oil to the circulation loop.

4. The hydraulic system according to claim 1, characterized in that, The hydraulic system also includes a pressure sensor (5) for detecting the pressure on the side of the hydraulic actuator (2) adjacent to the hydraulic resistance element (4).

5. The hydraulic system according to claim 4, characterized in that, The hydraulic system also includes a controller (6), which is electrically connected to the pressure sensor (5) and the hydraulic resistance element (4) respectively. The controller (6) is configured to control the opening of the hydraulic resistance element (4) based on the pressure detected by the pressure sensor (5).

6. The hydraulic system according to claim 5, characterized in that, The hydraulic system also includes an inverter (7), which is connected to the controller (6) and the motor (1). The inverter (7) is used to connect to a battery or an electrical appliance.

7. The hydraulic system according to any one of claims 1-6, characterized in that, The hydraulic resistance element (4) is a proportional control lift valve or a proportional control spool valve.

8. An engineering vehicle, characterized in that, The engineering vehicle includes the hydraulic system according to any one of claims 1-7, and further includes a working device, which is connected to the hydraulic actuator (2) in a transmission manner.

9. A control method for a hydraulic system, characterized in that, The control method of the hydraulic system implemented by any one of claims 1-8 includes: The load (9) has begun to decline; The actual pressure of the hydraulic fluid output by the hydraulic actuator (2) is obtained in real time; Compare the actual pressure with the set pressure; When the actual pressure exceeds the set pressure, the opening degree of the hydraulic resistance element (4) is adjusted based on the actual pressure; wherein, when the hydraulic resistance element (4) is fully open and the load (9) falls back, when the actual torque of the motor (1) is equal to the maximum torque allowed by the inverter (7), the pressure of the hydraulic fluid output by the hydraulic actuator (2) is the set pressure.

10. The control method for a hydraulic system according to claim 9, characterized in that, When the actual pressure does not exceed the set pressure, the hydraulic resistance element (4) remains fully open.

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