A four-quadrant variable displacement pump-controlled actuator system for an electric loader

Abstract

The application discloses a four-quadrant constant displacement pump control actuator system for an electric loader, and relates to the technical field of electric and hydraulic control of engineering machinery, and comprises the following steps: a power battery is connected to a direct current bus and supplies power to the direct current bus; an inverter is connected to the direct current bus; a four-quadrant motor is driven by the inverter; a constant displacement hydraulic pump is mechanically coupled with the four-quadrant motor to form an electro-hydraulic power unit; a relief valve group is connected between an outlet oil circuit of the constant displacement hydraulic pump and a system oil return circuit, and is used for realizing system overflow protection; the gravitational potential energy in the process of boom lowering and dump bed flattening is recovered by using the power generation condition of the four-quadrant motor, and is fed back to the power battery through a bidirectional inverter, and the actual energy consumption is only about one third of that of a traditional valve control system, and the energy efficiency of the system is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of electrification and hydraulic control technology of engineering machinery, and more specifically, to a four-quadrant displacement pump control actuator system for electric loaders. Background Technology

[0002] As a core piece of equipment in the construction machinery field, the performance of the hydraulic actuator system of an electric loader directly determines the overall operating efficiency, energy consumption level, and operational smoothness. Currently, most mainstream electric loaders employ either a "multi-pump independent drive" or "valve-controlled multi-actuator" hydraulic control scheme, but both have significant drawbacks: The multi-pump independent drive solution equips each hydraulic actuator (such as boom cylinder and dump cylinder) with a dedicated hydraulic pump and drive motor. Although it can achieve independent control of each actuator, it has problems such as a large number of components, high system complexity, large overall weight, and high cost. Moreover, the multi-pump coordinated control is difficult, which adds to the energy consumption and maintenance burden. The valve-controlled multi-actuator solution distributes flow by using a single pump in conjunction with a multi-way directional valve. Although the structure is relatively simple, it relies on valve port throttling to regulate flow and pressure, resulting in severe throttling losses, leading to extremely low system energy efficiency. Furthermore, hydraulic shock is easily generated when switching valve ports, causing problems such as actuator movement jerking and accelerated component wear. Existing solutions generally lack effective energy recovery mechanisms. During the operation of electric loaders, a large amount of gravitational potential energy generated by the lowering of the boom and the leveling of the bucket is mostly dissipated as heat energy through the throttle valve, resulting in energy waste. At the same time, when the actuators switch and the operating state changes, the parameters of the motor, hydraulic pump and valve group are poorly coordinated, which can easily lead to sudden torque changes and pressure spikes, further affecting the stability of operation and the life of the equipment. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a four-quadrant displacement pump-controlled actuator system for electric loaders. This system sequentially drives multiple hydraulic actuators using a single fixed-displacement hydraulic pump and utilizes the four-quadrant operating characteristics of the electric motor to achieve continuous and smooth energy recovery, thus solving the problems of low efficiency, high cost, and significant switching shocks in existing multi-actuator hydraulic control systems. This system aims to significantly reduce hydraulic energy loss and system cost while ensuring operational performance. Through this invention, a single-pump, multi-circuit electro-hydraulic system can achieve similar high efficiency and controllability to multi-pump systems, while avoiding valve-controlled throttling losses and shocks.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a four-quadrant displacement pump-controlled actuator system for an electric loader, comprising the following steps: a power battery connected to a DC bus and supplying power to the DC bus; an inverter with its input terminal connected to the DC bus; a four-quadrant motor driven by the inverter; a fixed displacement hydraulic pump mechanically coupled to the four-quadrant motor to form an electro-hydraulic power unit; an overflow valve group connected between the outlet oil circuit of the fixed displacement hydraulic pump and the system return oil circuit for system overflow protection; a function switching valve group connected between the outlet oil circuit of the electro-hydraulic power unit and each hydraulic actuator for connecting the outlet oil circuit of the electro-hydraulic power unit to the target hydraulic actuator; a proportional back pressure valve correspondingly disposed on the return oil circuit of each hydraulic actuator; a system sensor for collecting system status signals; and a controller with its signal input terminal connected to the system sensor and its control output terminal connected to the inverter, the function switching valve group, and each of the proportional back pressure valves.

[0005] According to one embodiment of the present invention, based on signals and operation commands collected by the system sensors, the target operating quadrant of the hydraulic actuator is identified in real time; according to the switching type of the target operating quadrant, a continuous and smooth reference trajectory of motor speed, motor torque, and proportional back pressure valve opening is planned and generated; using an electromechanical-hydraulic coupling prediction model including the equation of motor speed change rate and the equation of actuator working chamber pressure change rate, with the goal of tracking the reference trajectory, the model predictive control algorithm is used to solve the correction command of motor current command and proportional back pressure valve opening; zero torque dead zone compensation and feedforward compensation based on motor inductance parameters are applied to the solved motor current command, wherein the feedforward compensation amount is determined based on the derivative of the motor torque reference trajectory; the final control command is output and executed to complete the smooth switching of the operating quadrant.

[0006] According to one embodiment of the present invention, the system sensors include a motor sensor for acquiring the rotational speed and phase current of the four-quadrant motor, a voltage sensor for acquiring the DC bus voltage, a pressure sensor for acquiring the pressure difference between the inlet and outlet of the constant displacement hydraulic pump, an oil pressure sensor for acquiring the working chamber pressure of the hydraulic actuator, and an actuator speed sensor for acquiring the operating speed of the hydraulic actuator.

[0007] According to one embodiment of the present invention, during the process of switching from a first hydraulic actuator to a second hydraulic actuator, the controller is further configured to perform flow relay control, specifically: controlling the function switching valve group so that the closing sequence of the return oil circuit of the first hydraulic actuator partially overlaps with the opening sequence of the inlet oil circuit of the second hydraulic actuator, and using the model predictive control algorithm to precisely control the distribution of the output flow of the electro-hydraulic power unit between the two oil circuits during the overlap period.

[0008] According to one embodiment of the present invention, the controller includes a parameter identification module for online identification of the stator resistance and stator inductance of the four-quadrant motor; the controller dynamically adjusts the transition time constant of the switching process and the gain of the current loop controller based on the identified inductance value.

[0009] According to one embodiment of the present invention, the design of the continuous smooth reference trajectory must simultaneously meet the following constraints: the rate of change of motor torque does not exceed a preset threshold, the rate of change of proportional back pressure valve opening does not exceed the rated action rate of its valve group, and the pressure gradient of the hydraulic actuator working chamber does not exceed the safe allowable range.

[0010] According to one embodiment of the present invention, the specific method of zero torque dead zone compensation is as follows: the controller pre-stores a compensation mapping table or curve related to the dead zone characteristics of the four-quadrant motor; when performing compensation, it first determines whether the motor is in the low-speed operating zone or the medium-high speed operating zone based on the real-time collected motor speed, and calls the first-level compensation benchmark corresponding to the speed zone; then, based on the current direction and magnitude range of the motor torque command, the final compensation value is determined on the basis of the first-level compensation benchmark to eliminate the influence of dead zone on control accuracy.

[0011] According to one embodiment of the present invention, in the electromechanical-hydraulic coupling prediction model, the rate of change of motor speed is proportional to the difference between the electromagnetic torque of the motor and the load torque of the hydraulic pump, and the rate of change of pressure in the actuator working chamber is proportional to the difference between the output flow rate of the hydraulic pump and the net flow rate flowing into the working chamber.

[0012] According to one embodiment of the present invention, the inverter is a bidirectional three-phase voltage source inverter.

[0013] According to one embodiment of the present invention, the four-quadrant motor and the fixed displacement hydraulic pump are coaxially connected by a coupling and integrated in the same housing to form a compact electro-hydraulic power unit.

[0014] In summary, this application includes at least one of the following beneficial technical effects: 1. In this solution, the gravitational potential energy generated during the boom descent and bucket leveling process is recovered by utilizing the power generation mode of the four-quadrant motor. This energy is then fed back to the power battery via a bidirectional inverter. The measured energy consumption is only about one-third of that of the traditional valve control system, which significantly improves the system's energy efficiency and solves the core problems of high energy consumption and high cost in existing solutions.

[0015] 2. In this scheme, through flow relay control, continuous smooth reference trajectory planning and electromechanical-hydraulic coupling model predictive control, a shockless transition between actuator switching and operating quadrant switching is achieved.

[0016] 3. In this solution, the controller integrates an online parameter identification module, which can identify the stator resistance and inductance parameters of the four-quadrant motor in real time and dynamically adjust the transition time constant and current loop gain, so that the control strategy can adapt to changes in the motor's operating state. At the same time, the coordinated control of the proportional back pressure valve and the motor speed and torque not only achieves precise control of the actuator's movement speed, but also prevents the load from falling uncontrollably through back pressure constraints, which significantly improves the system's control robustness and operational safety, and is suitable for the complex and ever-changing working conditions of electric loaders. Attached Figure Description

[0017] Figure 1 This is a block diagram of the overall structure of the present invention; Figure 2 This is a continuous smooth reference trajectory diagram of the control variables during quadrant switching; Figure 3 This is a graph showing the pressure and flow response during actuator switching. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0020] Example 1, see Figure 1 This embodiment provides a four-quadrant displacement pump-controlled actuator system for an electric loader, including a power battery, a DC bus, an inverter, a four-quadrant motor, a fixed displacement hydraulic pump, an overflow valve assembly, a function switching valve assembly, a proportional back pressure valve, system sensors, a controller, and a hydraulic system. The actuators in this embodiment include a boom cylinder and a dump cylinder. The hydraulic system, consisting of a fixed displacement hydraulic pump, an overflow valve assembly, a function switching valve assembly, a proportional back pressure valve, a boom cylinder, a dump cylinder, and connecting pipelines, forms the hydraulic circuit for power transmission and motion control of the actuators.

[0021] The power battery provides high-voltage DC power to the system via the DC bus. The inverter is a bidirectional three-phase voltage source inverter, with its input connected to the DC bus and its output connected to a four-quadrant motor. In motor drive mode, the inverter converts the DC power into three-phase AC power to drive the motor; in motor generator mode, the inverter rectifies the AC power generated by the motor into DC power and feeds it back to the DC bus to charge the power battery.

[0022] The constant displacement hydraulic pump is a high-speed swashplate piston pump (or a gear pump). The four-quadrant motor is preferably a permanent magnet synchronous motor. The output shaft of the four-quadrant motor is connected to the input shaft of the constant displacement hydraulic pump, forming an electro-hydraulic power unit. Utilizing the four-quadrant characteristic allows for flexible control of the motor's torque and speed within each of the four quadrants. This significantly reduces the space occupied by components and minimizes transmission losses. Compared to a solution that requires an independent pump set for each actuator, this significantly reduces the number of hydraulic pumps, motors, and drivers, lowering system cost, complexity, and overall weight, while improving space utilization and economy.

[0023] The function switching valve group includes two two-position two-way electrically controlled directional valves, which control the oil circuit connection between the constant displacement hydraulic pump and the boom cylinder and tipping cylinder, respectively. Each cylinder's return oil circuit is equipped with a proportional back pressure valve, which is a pilot-operated electro-hydraulic proportional relief valve. Its set pressure is linearly regulated by the current signal output by the controller. The relief valve group is connected between the outlet oil circuit of the constant displacement hydraulic pump and the system return oil circuit to realize system overflow protection. The system sensors include a motor sensor, a voltage sensor, a pressure sensor, and an actuator speed sensor. The motor sensor is used to collect speed and phase current, the voltage sensor is used to collect DC bus voltage, the pressure sensor is used to collect pump inlet and outlet pressure difference and actuator working chamber pressure, and the actuator speed sensor is used to collect actuator running speed, providing signal support for the execution of the control strategy.

[0024] This system uses motor torque and speed as control signals for the four-quadrant motor. By controlling the speed and torque of the four-quadrant motor, the output flow and pressure of the fixed displacement hydraulic pump are adjusted to achieve actuator volumetric speed regulation and gravitational potential energy recovery.

[0025] The input to the electro-hydraulic power unit is a motor control signal, and the output is hydraulic power. The relationship between the two is as follows: The system generates the required electromagnetic torque by controlling the quadrature-axis current of the permanent magnet synchronous motor. This electromagnetic torque is equal to three-half the number of motor pole pairs, the product of the permanent magnet flux linkage and the quadrature-axis current, plus the sum of the difference between the direct-axis and quadrature-axis inductances, and the product of the direct-axis and quadrature-axis currents. For surface-mounted permanent magnet synchronous motors, the direct-axis and quadrature-axis inductances are equal. The above relationship can be simplified to the electromagnetic torque being equal to the product of the motor torque constant and the quadrature-axis current. This means the system can linearly control the drive or braking torque via electrical signals.

[0026] This enables the four-quadrant motor to operate in all four quadrants: The first quadrant represents forward motor drive. In this quadrant, the motor speed and torque are both positive, meaning the motor rotates forward and outputs driving torque. Simultaneously, the hydraulic pump rotates in the same direction, outputting positive flow. For example, when the boom cylinder performs a lifting action, the motor provides energy to overcome the gravity of the bucket and material, lifting the boom. The second quadrant represents reverse generation. In this quadrant, the motor speed is negative, and the torque is positive, but it is dragged in reverse by the load, entering a braking generation state. The load drives the actuator to move in the opposite direction. For example, when the boom cylinder descends from a high position under the gravity of the boom, bucket, and material, gravity drives the cylinder, and the hydraulic fluid drives the input shaft of the constant displacement hydraulic pump in reverse, causing the motor to generate electricity.

[0027] The third and fourth quadrants correspond to opposite motion conditions. The third quadrant is for motor reverse drive, where the motor speed and torque are negative; the motor reverses direction and outputs driving torque. The third quadrant also corresponds to the hydraulic pump rotating in reverse, outputting reverse flow. For example, driving the bucket cylinder to perform the bucket-retracting action requires the motor to provide energy to overcome the resistance of the bucket and material, retracting the bucket. The fourth quadrant is for motor forward power generation, where the motor speed is positive but the torque is negative; the motor rotates forward but is dragged in the opposite direction by the load, in a braking and power generation state. In this state, the load drives the actuator to move in the forward direction. For example, when the bucket cylinder is lowered from a high position under the weight of the bucket itself or the weight of the material inside, the weight of the bucket and the material drives the cylinder, i.e., the hydraulic fluid drives the input shaft of the constant displacement hydraulic pump to rotate forward, causing the motor to generate electricity.

[0028] In this embodiment, the first quadrant corresponds to the boom lifting process; the second quadrant corresponds to the boom lowering process; the third quadrant corresponds to the bucket tipping and retracting process; and the fourth quadrant corresponds to the bucket leveling process. The second and fourth quadrants both correspond to energy recovery conditions. Actual measurements show that the energy consumption of this system can be reduced to about one-third of that of a traditional valve-controlled system, significantly improving energy efficiency.

[0029] Furthermore, the function switching valve assembly is used to achieve time-sharing drive of a single pump to multiple actuators. In this embodiment, it includes two two-position, two-way electrically controlled directional valves. The first directional valve controls the on / off state of the oil circuit between the constant displacement hydraulic pump and the boom cylinder, and the second directional valve controls the on / off state of the oil circuit between the constant displacement hydraulic pump and the bucket cylinder. The control system is configured to ensure that at any given time of operation, only one directional valve is in the open state, thereby directionally distributing the hydraulic output of the constant displacement hydraulic pump to either the boom cylinder or the bucket cylinder.

[0030] A proportional back pressure valve is also installed at the return port of each hydraulic cylinder. A first proportional back pressure valve is installed on the return line of the boom cylinder, and a second proportional back pressure valve is installed on the return line of the bucket cylinder. The function of installing the proportional back pressure valve is to provide appropriate back pressure when the actuator is in a downward or inertial drive condition, preventing uncontrolled load descent and uncontrolled hydraulic flow. In other words, when the hydraulic cylinder extends under gravity, such as when the boom is descending, the back pressure valve acts as a load holding and speed control valve, ensuring that the descent speed is controlled by limiting the oil flow and preventing it from being too fast due to gravity. Both the first and second proportional back pressure valves are pilot-operated electro-hydraulic proportional relief valves, and their set pressure is linearly controlled by the current signal output by the control system.

[0031] Example 2 addresses the hydraulic shock problem during actuator switching and quadrant switching by employing flow relay, model predictive control, and compensation strategies, achieving a smooth transition. This example specifically includes the following steps: Step 1: Determine the operating quadrant.

[0032] The controller collects signals from all system sensors in real time (including the speed and phase current of the four-quadrant motor, DC bus voltage, inlet and outlet pressure difference of the constant displacement hydraulic pump, working chamber pressure of each hydraulic actuator, and operating speed of each hydraulic actuator). Simultaneously, it receives operator joystick commands and uses a built-in load force estimation algorithm to estimate the load force borne by each hydraulic actuator in real time. This algorithm integrates the dynamic data collected by the sensors with pre-stored inherent parameters such as actuator structural parameters, equivalent mass, and friction models. Based on the principles of mechanics and hydraulic transmission, it decomposes the total load force into hydraulic driving force, inertial force, gravity component, mechanical resistance, and hydraulic leakage compensation force, and performs vector synthesis. This is then achieved through electromechanical-hydraulic coupling. The combined correction and online adaptive correction improve estimation accuracy. The electromechanical-hydraulic coupling relationship is based on the mechanical coupling relationship between the four-quadrant motor and the fixed displacement hydraulic pump, as well as the dynamic relationship between the electromagnetic torque of the motor and the load torque of the hydraulic pump. The controller identifies the current operating quadrant of each hydraulic actuator in real time based on the motion direction of the hydraulic actuator and the load force direction estimated above. It also predicts the next target operating quadrant according to the joystick command. Then, based on the correspondence between the current operating quadrant and the target operating quadrant, it determines the type of switching that needs to be performed (including switching between operating quadrants of the same hydraulic actuator and switching between different hydraulic actuators). This provides a key basis for subsequent control strategy optimization and ensures efficient and stable operation of the system.

[0033] For example, when the boom cylinder is currently lifting a load, it is in the first quadrant; if the operator issues a boom lowering command, the target operating quadrant is the second quadrant, and the switching type is the same hydraulic actuator operating quadrant switching.

[0034] Step 2: Plan a smooth switching trajectory.

[0035] Based on the switching type identified in step one, the controller plans a continuously differentiable smooth reference trajectory for the control variables, which include the speed of the four-quadrant motor, the torque of the four-quadrant motor, and the opening degree of the target proportional back pressure valve.

[0036] See Figure 2 The graph shows the smoothing reference trajectory of the control variables during this switching process. The graph forms three curves on the same time axis (0-2s). Curve A is the reference trajectory of the motor torque, with an initial value of 100 N·m, which transitions exponentially to the target value of -80 N·m. The torque change rate never exceeds the preset threshold, and there is no sudden torque change. Curve B is the reference trajectory of the proportional back pressure valve opening, with the opening value linearly decreasing from the initial 100% to 30%. The opening change rate is strictly limited to the rated action rate of 20% / s, and the valve core moves smoothly without jamming. Curve C is the reference trajectory of the actuator working chamber pressure, with the pressure value smoothly transitioning from the initial 15 MPa to the target value of 5 MPa. The pressure gradient is always controlled within the safe range of 30 MPa / s.

[0037] During actuator quadrant switching and transitions between different actuator operating conditions, the continuous, abrupt changes in the three curves mentioned above ensure a smooth and synchronous transition of operating parameters for the motor, hydraulic valve assembly, and actuator, effectively avoiding hydraulic and electrical shocks caused by sudden parameter changes. When the controller plans the reference trajectory (curve A), the torque change rate of the four-quadrant motor does not exceed a preset threshold to prevent motor current surges. The opening change rate of the proportional back pressure valve does not exceed the rated operating rate of its valve assembly to ensure the valve core accurately tracks control commands (curve B). The pressure gradient in the hydraulic actuator's working chamber does not exceed the safe allowable range to protect hydraulic system components from pressure surge damage (curve C).

[0038] Step 3: Electromechanical-hydraulic coupling model predictive control.

[0039] The controller incorporates an electromechanical-hydraulic coupling prediction model, whose dynamic relationships include: First, the relationship between the rate of change of motor angular velocity: The rate of change of angular velocity of a four-quadrant motor is proportional to the difference between the electromagnetic torque of the motor and the load torque of the constant displacement hydraulic pump. Second, the relationship of the pressure change rate of the actuator working chamber: The pressure change rate of the hydraulic actuator working chamber is proportional to the difference between the output flow rate of the constant displacement hydraulic pump and the net flow rate flowing into the working chamber (i.e., the difference between the flow rate consumed by the hydraulic actuator and the leakage flow rate).

[0040] After completing the continuous smooth reference trajectory planning in step two and determining the three physical constraints—motor torque change rate not exceeding a preset threshold, proportional back pressure valve opening change rate not exceeding its rated action rate, and hydraulic actuator working chamber pressure gradient not exceeding the safety allowable range—model predictive control algorithm is adopted to achieve coordinated optimization control of motor drive and hydraulic back pressure. Specifically, within each control cycle (e.g., 1 millisecond), the main optimization objective is to accurately track the preset reference trajectory with the system output (including four-quadrant motor speed and hydraulic actuator working chamber pressure) over the next few control cycles. Simultaneously, the algorithm ensures that the motor torque change rate does not exceed the preset threshold and the proportional back pressure valve opening rate does not exceed the safety allowable range. The optimization problem is defined by three physical constraints: the rate of change of the degree of change of the valve group does not exceed the rated action rate of the valve group, and the pressure gradient of the hydraulic actuator working chamber does not exceed the safe allowable range. Based on the electromechanical-hydraulic coupling prediction model (including the correlation between the rate of change of the motor angular velocity and the motor electromagnetic torque and the hydraulic pump load torque, and the correlation between the rate of change of the actuator working chamber pressure and the hydraulic pump output flow and the working chamber net flow), the constrained optimization problem is processed by rolling solution method. Finally, the optimal motor quadrature axis current command (used to generate the required motor electromagnetic torque) and the correction command of the proportional back pressure valve opening degree in the current control cycle are output to achieve the coordinated optimization control of the two.

[0041] Step 4: Actuator switches to flow relay control.

[0042] When the switching type is a switch between different hydraulic actuators (such as switching from the first hydraulic actuator to the second hydraulic actuator), the controller additionally performs flow relay control. The specific control logic is as follows: The controller precisely controls the timing of the switching valve group's actions, causing the closing timing of the original working hydraulic actuator (first hydraulic actuator) return oil circuit to partially overlap with the opening timing of the target working hydraulic actuator (second hydraulic actuator) inlet oil circuit. During the timing overlap, the output flow of the constant displacement hydraulic pump will flow to both oil circuits simultaneously. The controller uses the electromechanical-hydraulic coupling model predictive control algorithm in step three to precisely control the distribution ratio of the constant displacement hydraulic pump output flow between the two oil circuits during the overlap period by coordinating the adjustment of the speed of the four-quadrant motor (thereby adjusting the total output flow of the constant displacement hydraulic pump) and the opening degree of the proportional back pressure valves corresponding to the two oil circuits. This ensures a smooth transition of the total system flow and pressure, achieving seamless flow relay and avoiding hydraulic shock during the switching process.

[0043] See Figure 3The figure shows the pressure and flow response curves during actuator switching. The figure contains three curves on the same time axis. Curve D is the hydraulic pump outlet pressure change curve. The initial pressure is maintained at 14MPa from 0-1s, and the pressure smoothly transitions to the target pressure of 10MPa during the switching phase from 1-1.5s, without pressure spikes or cliff-like pressure drops throughout the process. Curve E is the boom cylinder flow change curve. After switching, the flow rate decreases steadily from 50L / min to 0. Curve F is the bucket cylinder flow change curve. The flow rate increases steadily from 0 to 45L / min simultaneously.

[0044] When the electric loader switches from boom cylinder operation mode to dump cylinder operation mode, the hydraulic pump outlet pressure transitions smoothly without hydraulic shock. The flow of the two actuators forms a complementary flow relay, realizing seamless distribution of hydraulic pump output flow and ensuring that there is no flow waste or impact disturbance during the switching process.

[0045] The hydraulic pump outlet pressure is shown in curve D. During actuator switching, the pump outlet pressure exhibits no spikes or abrupt pressure drops, demonstrating pressure stability. After switching (when the tipping cylinder is operating), the hydraulic pump outlet maintains a stable operating pressure.

[0046] The boom cylinder flow rate is shown in curve E. Before switching, the boom cylinder receives a stable flow rate from the hydraulic pump. During actuator switching, the hydraulic flow to the boom cylinder is gradually cut off, indicating that it stops working. After switching, the boom cylinder receives no flow and remains stationary.

[0047] The flow rate of the tipping cylinder is shown in curve F. Before the switch, the tipping cylinder was not working and there was no flow input. During the actuator switchover, the oil flow to the tipping cylinder is gradually connected, indicating that it has started working. After the switchover, when the tipping cylinder is working, the hydraulic pump provides it with a stable flow rate.

[0048] Therefore, the switching zone is 1-1.5s, which is the execution phase from the boom cylinder to the tipping cylinder. During this period, the boom flow rate decreases and the tipping flow rate increases to form a flow relay. At the same time, the pump port pressure transitions smoothly, achieving a switching without impact or flow waste.

[0049] Step 5: Automatic compensation of control commands.

[0050] First, the motor quadrature-axis current command obtained in step three is subjected to dual compensation, specifically including: Zero-torque dead-zone compensation: To eliminate the control nonlinearity problem near zero torque caused by the inverter switching dead zone, the controller pre-stores a dead-zone characteristic compensation mapping table or compensation curve corresponding to the four-quadrant motor and inverter combination. During compensation, a two-level compensation strategy is adopted: First, based on the real-time collected four-quadrant motor speed, it is determined whether the motor is currently in the low-speed or medium-high-speed operating zone, and the first-level compensation benchmark corresponding to the speed zone is called. Then, based on the current motor torque command direction and torque magnitude range, the final zero-torque dead-zone compensation value is determined on the basis of the first-level compensation benchmark, and this compensation value is superimposed on the motor quadrature-axis current command to eliminate the influence of dead zone on control accuracy.

[0051] Feedforward compensation based on inductance parameters: In order to improve the dynamic response speed of the current loop, a feedforward compensation amount based on the motor inductance parameters is introduced. This feedforward compensation amount is proportional to the derivative of the motor torque reference trajectory, and its proportionality coefficient includes the stator inductance parameters of the four-quadrant motor.

[0052] Second, online parameter identification and adaptive adjustment.

[0053] The controller has a built-in parameter identification module for online real-time identification of the stator resistance and stator inductance of the four-quadrant motor; based on the identified stator inductance value, the controller dynamically adjusts these two control parameters: Adjust the transition time constant of the switching process to match the dynamic characteristics of the reference trajectory with the electrical time constant of the current four-quadrant motor; and adjust the gain of the current loop controller (such as a PI regulator) to maintain the optimal bandwidth and operational stability of the current loop, adapting to the characteristics of motor parameters changing with operating conditions.

[0054] Step Six: Control Instruction Synthesis and Execution.

[0055] The controller synthesizes the final control commands: First, the motor current command: The final motor current command is the sum of the motor quadrature axis current command obtained by the model predictive control algorithm, the zero torque dead zone compensation value, and the feedforward compensation value based on the inductance parameters. This command drives the four-quadrant motor to run through the current loop and the inverter. Second, the proportional back pressure valve opening command: The final proportional back pressure valve opening command is the sum of the proportional back pressure valve opening reference trajectory command planned in step two and the proportional back pressure valve opening correction command obtained in step three. This command is output to the corresponding proportional back pressure valve. Third, timing commands for function switching valve groups: The controller sends precise timing control commands to the function switching valve groups to control the on / off state of the directional valves.

[0056] All control commands are executed synchronously, and the drive system completes a highly smooth quadrant switching or hydraulic actuator switching.

[0057] Furthermore, the flow characteristics of the proportional back pressure valve satisfy the following: the oil flow rate through the proportional back pressure valve is equal to the product of the flow coefficient, the valve opening of the proportional back pressure valve, and the square root of the term, where the square root of the term is twice the ratio of the absolute value of the pressure drop at the valve opening of the proportional back pressure valve to the oil density; the valve opening of the proportional back pressure valve is adjusted by the control signal output by the controller. Through this adjustment mechanism, the movement speed can be precisely controlled when the hydraulic actuator is lowered, and pressure fluctuations can be absorbed at the moment of switching, further ensuring the stability of the system operation.

[0058] The specific work process is as follows: Boom lifting operation: When the operator gives the boom lifting signal, the system first controls the first directional valve in the function switching valve group to open and the second directional valve to close; then controls the four-quadrant motor to work in the first quadrant, and the motor rotates in the forward direction to drive the constant displacement hydraulic pump to run; the pressure oil output by the constant displacement hydraulic pump enters the rodless chamber of the boom cylinder through the first directional valve, pushing the piston rod to extend, thereby lifting the boom and the material in the bucket; at this time, the oil in the rod chamber of the boom cylinder flows back to the oil tank through the corresponding first proportional back pressure valve (the opening degree is set according to the control requirements); during this process, the movement speed of the hydraulic actuator is directly controlled by the speed of the four-quadrant motor, and the lifting force is indirectly controlled by the torque of the four-quadrant motor, and there is no throttling loss in the whole process.

[0059] Switching from boom lifting to bucket tipping: When switching from boom lifting to bucket tipping, the controller executes the smooth switching control method described above: First, model predictive control is used to balance the pump inlet pressure of the fixed displacement hydraulic pump with the boom circuit pressure; then, flow relay control is executed to smoothly transition the hydraulic output from the boom circuit to the bucket circuit; after the flow is completely switched, the boom circuit is completely disconnected; finally, the four-quadrant motor is controlled to enter the third or fourth quadrant to drive the bucket cylinder to perform the bucket tipping action; throughout the switching process, the system pressure and flow transition smoothly without hydraulic shock.

[0060] Boom lowering operation: When the boom needs to be lowered, the controller switches the control function switching valve group to reconnect the boom circuit and controls the four-quadrant motor to smoothly transition from the first quadrant to the second quadrant (forward power generation operation); by coordinating the control of the generating torque of the four-quadrant motor (to realize the recovery of gravitational potential energy) and the opening of the first proportional back pressure valve (to control the boom lowering speed), a smooth and controllable lowering of the boom is achieved.

[0061] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A four-quadrant displacement pump-controlled actuator system for an electric loader, characterized in that: Including the following steps: A power battery, which is connected to the DC bus and supplies power to the DC bus; Inverter, the input of which is connected to the DC bus; A four-quadrant motor, which is driven by the inverter; A fixed displacement hydraulic pump is mechanically coupled to the four-quadrant motor to form an electro-hydraulic power unit; An overflow valve assembly is connected between the outlet oil circuit of the constant displacement hydraulic pump and the system return oil circuit to realize system overflow protection; A function switching valve assembly is connected between the outlet oil circuit of the electro-hydraulic power unit and each hydraulic actuator, and is used to connect the outlet oil circuit of the electro-hydraulic power unit to the target hydraulic actuator. A proportional back pressure valve is correspondingly installed on the return oil line of each of the hydraulic actuators; System sensors are used to collect system status signals; The controller has its signal input terminal connected to the system sensor, and its control output terminal connected to the inverter, the function switching valve group, and each of the proportional back pressure valves.

2. The four-quadrant limited displacement pump control actuator system for an electric loader according to claim 1, characterized in that: Based on the signals and operation commands collected by the system's sensors, the target operating quadrant of the hydraulic actuator can be identified in real time. Based on the switching type of the target operating quadrant, plan and generate a continuous and smooth reference trajectory for motor speed, motor torque and proportional back pressure valve opening; Using an electromechanical-hydraulic coupling prediction model that includes the equations for the rate of change of motor speed and the rate of change of pressure in the actuator working chamber, with the goal of tracking the reference trajectory, the model predictive control algorithm is used to solve the correction commands for the motor current command and the proportional back pressure valve opening in a rolling manner. Zero torque dead zone compensation and feedforward compensation based on motor inductance parameters are applied to the solved motor current command, wherein the amount of feedforward compensation is determined based on the derivative of the motor torque reference trajectory; Output and execute the final control command to complete a smooth switch between operating quadrants.

3. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 1, characterized in that: The system sensors include a motor sensor for acquiring the speed and phase current of the four-quadrant motor, a voltage sensor for acquiring the DC bus voltage, a pressure sensor for acquiring the pressure difference between the inlet and outlet of the constant displacement hydraulic pump, an oil pressure sensor for acquiring the working chamber pressure of the hydraulic actuator, and an actuator speed sensor for acquiring the operating speed of the hydraulic actuator.

4. A four-quadrant displacement pump-controlled actuator system for an electric loader according to claim 2, characterized in that: During the switching from the first hydraulic actuator to the second hydraulic actuator, the controller is also configured to perform flow relay control, specifically: The function switching valve group is controlled so that the closing timing of the return oil circuit of the first hydraulic actuator partially overlaps with the opening timing of the inlet oil circuit of the second hydraulic actuator, and the model predictive control algorithm is used to precisely control the distribution of the output flow of the electro-hydraulic power unit between the two oil circuits during the overlap period.

5. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 4, characterized in that: The controller includes a parameter identification module for online identification of the stator resistance and stator inductance of the four-quadrant motor; the controller dynamically adjusts the transition time constant of the switching process and the gain of the current loop controller based on the identified inductance value.

6. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 2, characterized in that: The design of the continuous smooth reference trajectory must simultaneously meet the following constraints: the rate of change of motor torque does not exceed a preset threshold, the rate of change of proportional back pressure valve opening does not exceed the rated action rate of its valve group, and the pressure gradient of the hydraulic actuator working chamber does not exceed a preset safety allowable range.

7. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 2, characterized in that: The specific method for zero-torque dead-zone compensation is as follows: The controller has a pre-stored compensation mapping table or curve related to the dead zone characteristics of the four-quadrant motor. When performing compensation, the motor speed is first determined to be in the low-speed or medium-to-high-speed operating range based on the real-time collected motor speed, and the first-level compensation benchmark corresponding to that speed range is called. Subsequently, based on the current direction and magnitude range of the motor torque command, and on the basis of the first-level compensation benchmark, the final compensation value is determined to eliminate the impact of dead zone on control accuracy.

8. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 2, characterized in that: In the electromechanical-hydraulic coupling prediction model, the rate of change of motor speed is proportional to the difference between the electromagnetic torque of the motor and the load torque of the hydraulic pump, and the rate of change of pressure in the actuator working chamber is proportional to the difference between the output flow rate of the hydraulic pump and the net flow rate flowing into the working chamber.

9. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 8, characterized in that: The inverter is a bidirectional three-phase voltage source inverter.

10. A four-quadrant limited displacement pump control actuator system for an electric loader according to claim 9, characterized in that: The four-quadrant motor and the fixed displacement hydraulic pump are coaxially connected via a coupling and integrated into the same housing to form a compact electro-hydraulic power unit.

Images