A pump-valve parallel steering control system for heavy vehicles and a working method thereof

Abstract

The application provides a pump-valve parallel steering control system for heavy vehicles and a working method thereof. A steering wheel of the vehicle is connected with a folding angle of a steering execution module. The folding angle is driven by a steering assist cylinder piston. The folding angle has a unique corresponding relationship with a displacement of the steering assist cylinder piston. A wheel angle control signal is converted into a steering assist cylinder piston displacement signal and a flow signal to perform feedforward control of steering operation. In combination with feedback control, a closed loop control is formed. Specifically, after receiving a folding angle feedback signal, a comparison calculation is performed with a steering control signal. In combination with a received load pressure signal, a hydraulic mechanism pump-valve loop flow is adjusted in real time. The steering assist cylinder piston is controlled to control the folding angle to rotate, to perform steering control, and to form a closed loop steering feedback control. The application is suitable for steering control of a hybrid heavy multi-axle vehicle. High energy efficiency, high dynamics and emergency control ability can be considered, and safety redundancy is provided.

Description

Technical Field

[0001] This invention relates to the field of control system technology applicable to hybrid vehicles, and in particular to a pump-valve parallel steering control system for heavy-duty vehicles and its operating method. Background Technology

[0002] With the steady progress of large-scale infrastructure construction and the Belt and Road Initiative in China, the demand for specialized transshipment of large cargo serving economic infrastructure development is increasing daily. Heavy-duty multi-axle transport vehicles are the core tools for specialized transshipment of large cargo, and the performance of their electro-hydraulic steering systems directly determines transshipment efficiency, thereby affecting the construction progress.

[0003] Currently, most electro-hydraulic steering systems in heavy-duty multi-axle transport vehicles employ a single pump-controlled or valve-controlled drive method. This drive method has several drawbacks when dealing with the long distances, complex road conditions, and diverse driving modes required for transporting large special equipment. For example, during high-speed operation on straight roads, good mid-range control precision is required, and the poor dynamic performance of a single pump-controlled system will limit steering performance. During operation on mountain roads with continuous large turns, the steering load is high, and the throttling control method of a single valve-controlled system will generate significant energy consumption. Furthermore, as the load on heavy vehicles continues to increase, the probability of failure of a single control system is constantly rising, leading to an increased probability of transport accidents.

[0004] Therefore, it is urgent to further explore new electro-hydraulic steering solutions based on the existing single-drive steering system in order to improve the overall steering performance of heavy multi-axle transport equipment in multiple driving modes during special transportation.

[0005] In other fields where hydraulic systems are the primary control method, researchers have attempted to introduce parallel pump-valve coordinated design schemes to address similar problems, achieving good results in research objects such as aviation EHA (Electronic Hydraulic Axle) systems, hydraulic excavators, and cranes. This scheme connects the pump control circuit and the valve control circuit in parallel, theoretically combining the high energy efficiency of the pump control circuit with the high dynamics of the valve control circuit, and also providing redundancy backup. Therefore, applying this to heavy-duty multi-axle transport equipment to form a pump-valve coordinated electro-hydraulic steering system is a potentially feasible approach to meet the requirements for steering dynamics, energy efficiency, and safety under various driving modes.

[0006] However, compared with traditional single-drive methods, the pump-valve parallel control scheme is still immature, and there is currently no relevant research in the field of vehicle steering. Applying it to heavy-duty vehicle steering requires overcoming many technical challenges. For example, the coupling characteristics of pumps and valves in the steering system have not yet been fully explored, making system parameter configuration difficult; heavy-duty vehicles have many driving modes, each with different steering performance requirements, making it difficult to achieve high steering performance in all modes; the flow ratio of the pump-controlled and valve-controlled loops directly affects the system's energy efficiency and safety redundancy performance, making it difficult to balance high energy efficiency and high safety redundancy. Summary of the Invention

[0007] This invention proposes a pump-valve parallel steering control system and its working method for heavy-duty vehicles. It is the first heavy-duty vehicle steering system and its control strategy based on pump-valve parallel control, which is applicable to the steering control of hybrid heavy-duty multi-axle vehicles. It enables the system to balance high energy efficiency and high dynamics while maintaining a certain emergency control capability and providing a certain degree of safety redundancy.

[0008] The present invention adopts the following technical solution.

[0009] A pump-valve parallel steering control system for heavy-duty vehicles is disclosed. A pair of steering wheels of the heavy-duty vehicle are connected to the steering execution module of the pump-valve parallel steering control system at an angle. The angle is driven by the piston of the power steering cylinder, and there is a unique correspondence between the angle of rotation and the displacement of the power steering cylinder piston. The pump-valve parallel steering control system uses a relational equation to convert the wheel angle control signal into a power steering cylinder piston displacement signal. Then, the piston displacement signal is converted into a flow signal and a control element voltage signal for a feedforward control stage of closed-loop steering operation. Subsequently, closed-loop control is performed in conjunction with feedback control. Specifically, after receiving the wheel angle feedback signal measured by the sensor, the controller of the pump-valve parallel steering control system compares and calculates it with the steering control signal. Combined with the received load pressure signal, it adjusts the flow rate of the hydraulic mechanism's pump-valve circuit in real time, outputting hydraulic oil of the required flow rate and direction to the power steering cylinder to control the displacement of the power steering cylinder piston and thus control the angle rotation. This causes the steering wheels to rotate with the angle to execute steering control, forming precise steering feedback control.

[0010] When the heavy vehicle has two or more pairs of steering wheels for steering control, the heavy vehicle uses multiple pump-valve parallel steering control systems to perform combined control of the steering process. Each pair of steering wheels is connected at an angle to a corresponding pump-valve parallel steering control system steering execution module.

[0011] The hydraulic mechanism of the pump-valve parallel steering control system includes a controller, pump control circuit, valve control circuit, steering execution module, etc.

[0012] The pump control circuit includes a servo pump unit (composed of a fixed displacement pump and a servo motor) responsible for flow control, a directional valve responsible for flow direction control, and an overflow valve component responsible for unloading and safety assurance.

[0013] The valve control circuit includes a metering pump and motor responsible for providing flow, a flow divider responsible for distributing the metering pump flow to multiple systems, an electro-hydraulic servo valve responsible for flow and direction control, and an overflow valve element responsible for pressure control.

[0014] The steering execution module includes a left steering assist cylinder and a right steering assist cylinder connected in parallel, as well as a trapezoidal steering mechanism controlled by it; the trapezoidal steering mechanism is a hinged four-bar linkage with one degree of freedom consisting of an axle frame, two steering angles and a long shaft, and the cylinder bodies and extension rods of the left and right steering assist cylinders are connected to the frame and the left and right angles respectively through hinges;

[0015] The pump control circuit, valve control circuit, and steering actuator are connected via parallel valve blocks and pipelines.

[0016] In the pump-valve parallel steering control system, the pump control circuit and the valve control circuit are two control circuits with independent power components and control components. When one circuit fails, the other circuit can work normally, so that the pump-valve parallel steering control system can maintain a certain emergency control capability and provide a certain safety redundancy.

[0017] When the heavy-duty vehicle is a hybrid vehicle, the power system of the vehicle needs to reserve a portion of the power to the pump control circuit to ensure the normal operation of the steering system when distributing energy.

[0018] In the extreme case where the hybrid vehicle's power is completely depleted and the pump control circuit driven by the electric motor in the pump-valve parallel steering control system fails, the valve control circuit of the pump-valve parallel steering control system switches to the internal combustion engine drive of the hybrid vehicle, so that the hybrid vehicle retains some steering ability and provides a certain degree of safety for the vehicle.

[0019] The working method of the pump-valve parallel steering control system for heavy vehicles uses the above-described pump-valve parallel steering control system for heavy vehicles. When the hydraulic mechanism of the pump-valve parallel steering control system is working, most of the pressure oil is provided by the high-efficiency pump control circuit to improve the system energy efficiency. The flow rate of the valve control circuit is supplemented on the basis of the pump control flow rate to improve the dynamic control accuracy of the pump-valve parallel steering control system. Under the premise of ensuring valve control accuracy, the flow rate of the valve control circuit is reduced as much as possible to balance the advantages of high energy efficiency of the pump control circuit and high dynamics of the valve control circuit.

[0020] Considering the safety redundancy in case of pump control circuit failure, the upper limit of the flow rate that the valve control circuit can provide cannot be too low. Therefore, the flow rate of the fixed displacement pump and the rated flow rate of the servo valve cannot be set too small. When used for multi-axle control of heavy vehicles, the valve control circuits of multiple pumps and valves in parallel steering control systems that correspond one-to-one with multiple pairs of steering wheels of heavy vehicles share a single fixed displacement pump for oil supply and use a flow divider block to split the flow, so as to maintain a large upper limit of flow output while the normal flow rate of a single valve control circuit is low.

[0021] When the pump-valve parallel steering control system is working, it first converts the steering angle control signal used for steering operation of heavy vehicles into the total flow signal of the hydraulic mechanism of the pump-valve parallel steering control system through the relationship equation between the piston displacement of the steering power cylinder and the wheel angle. Then, based on the total flow signal, the pump control circuit performs feedforward control. Finally, based on the deviation between the steering angle control signal and the actual steering angle, the pump control circuit and the valve control circuit jointly perform PID control to form a closed-loop control.

[0022] When the pump-valve parallel steering control system is working, the wheel rotation angle is measured by the angular displacement sensor installed at the bend.

[0023] The derivation process of the equation relating the power steering cylinder piston displacement and the wheel rotation angle is as follows:

[0024] First, the relationship between the steering angles of the left and right wheels in a pair of steering wheels (measured by an angular displacement sensor installed at the corner) is derived using the following formula:

[0025] Formula 1;

[0026] In the formula, α and β are the steering angles of the left and right tires, respectively; m is the length of the steering angle; L is the length of the tie rod in the pair of steering wheels; γ is the angle at which the steering knuckle arm intersects the axle; B is the distance between the kingpins of the two steering knuckle arms at the axle where the pair of steering wheels are located; and k is the distance from the kingpin of the left knuckle arm to the end of the right knuckle arm.

[0027] Next, the piston displacement x of the left and right power steering cylinders is adjusted. L and x R The left and right wheel rotation angles are used to indicate:

[0028] Formula 2;

[0029] In the formula, n is the distance between the hinge connecting the axle frame and the hinge connecting the power steering cylinder extension rod at the steering angle.

[0030] Then, the flow rate Q required for vehicle steering is calculated by taking the derivative of the power steering cylinder piston displacement as the velocity:

[0031] Formula 3;

[0032] In the formula, A and a are the areas of the rodless chamber and the rod chamber of the power steering cylinder, respectively, and the symbols represent the control direction of the servo valve and the directional valve.

[0033] The specific method for calculating the control voltage of feedforward control is as follows: Match the output flow of the hydraulic system to the flow required for steering by the steering actuator module. Utilizing the relationship between the hydraulic mechanism's output flow and the control voltage, and based on the set distribution ratio (the feedforward flow is mainly provided by the pump control circuit to improve energy efficiency), the required feedforward control signal is calculated in reverse.

[0034] Formula 4;

[0035] In the formula, q p and q v D represents the flow rates of the pump-controlled and valve-controlled circuits, respectively. p For pump displacement; k m u1 and u2 are the speed gain and control voltage of the servo motor, respectively; C d ω is the flow coefficient; u2 is the valve opening gain; ρ is the valve core control voltage; p is the oil density. p p1 is the pump source pressure, and p2 is the load chamber pressure.

[0036] The derivation of the control equations for PID feedback control is as follows:

[0037] First, based on the desired rotation angle control signal β d The control deviation e is calculated using the actual feedback signal β of the turning angle:

[0038] Formula 5;

[0039] The PID controller is as follows:

[0040] Formula 6;

[0041] In the formula, K p K is the proportionality coefficient. i K is the integral coefficient. d is the differential coefficient.

[0042] The PID feedback control signal is derived using Formula 4. The feedback control is mainly performed by the valve control loop to improve the system control accuracy of the pump-valve parallel steering control system.

[0043] This invention achieves a balance between dynamic performance, energy efficiency, and safety requirements for heavy-duty vehicle steering systems under various driving modes. Utilizing a parallel pump-valve coordinated control scheme, it integrates the high energy efficiency of the pump control circuit and the high dynamic performance of the valve control circuit, effectively solving various performance deficiencies of traditional single-drive systems when dealing with complex road conditions and multiple driving modes. Furthermore, because the two control circuits have independent power and control components, when one circuit fails, the other can still operate normally, maintaining a certain level of emergency control capability and providing a degree of safety redundancy. In addition, when applied to hybrid vehicles, in the extreme case where the power is completely depleted and the electric motor-driven pump control circuit fails, the valve control circuit switches to internal combustion engine drive, preserving some steering capability and providing a certain level of safety assurance for the vehicle.

[0044] The main advantage of this invention lies in its ability to improve the overall control accuracy of the system through the valve-controlled circuit. However, since the pump-controlled circuit provides most of the flow, its dynamic characteristics also affect the overall control accuracy. Therefore, this invention uses a servo motor to drive the hydraulic pump in the pump-controlled circuit. Simultaneously, by utilizing the servo motor's ability to start and stop on and off, the overall energy consumption of the system can be further reduced. In the valve-controlled circuit, since it is mainly controlled by a servo valve, it can be driven by a traditional internal combustion engine, or by an electric motor like the pump-controlled circuit, or by a hybrid power system. Furthermore, due to the large load and long transport distance of heavy-duty multi-axle vehicles, the range of pure electric power still needs further development. Therefore, this invention is mainly applicable to the steering control of hybrid heavy-duty multi-axle vehicles, but it can also be used in pure electric heavy-duty multi-axle vehicles in the future. It should be noted that when used in hybrid vehicles, since the pump-controlled circuit uses a pure electric solution, a portion of the power needs to be reserved during energy distribution to ensure the normal operation of the steering system.

[0045] The advantages of this invention are:

[0046] (1) An innovative combination of parallel pump-valve collaborative design and heavy vehicle steering system has been achieved. The parallel pump-valve collaborative control scheme has been successfully applied in some situations, but it has not yet been applied in the field of vehicle steering control. This invention combines it with heavy vehicle steering system and achieves better control effect, pioneering a heavy vehicle steering system and its control strategy based on pump-valve parallel control.

[0047] (2) It achieves a balance between the dynamic, energy efficiency, and safety requirements of the steering system for heavy-duty vehicles under various driving modes. By utilizing a parallel pump-valve coordinated control scheme, it integrates the advantages of high energy efficiency of the pump control loop and high dynamics of the valve control loop, effectively solving the various performance deficiencies of the traditional single drive mode when dealing with multiple driving modes under complex road conditions. At the same time, since the two control loops have independent power and control components, when one loop fails, the other loop can still work normally, enabling the system to maintain a certain emergency control capability and providing a certain degree of safety redundancy.

[0048] (3) Achieving a balance between high safety redundancy and high energy efficiency in the parallel pump-valve coordinated control scheme. In the parallel pump-valve coordinated control scheme, the pump control loop provides the main pressure oil, while the valve control loop outputs a smaller flow rate to balance high energy efficiency and high dynamics. However, the smaller flow rate of the valve control loop leads to poor safety redundancy in the event of a pump control loop failure, resulting in a conflict between energy efficiency and safety redundancy. This invention is mainly applied to heavy-duty multi-axle vehicles, which typically have multiple pairs of steering wheels responsible for steering control. Each pair of steering wheels is controlled by a set of pump-valve parallel control systems. Each pump control loop is supplied with pressure oil by its own servo pump, while the valve control loop is supplied with oil to all systems by a fixed-displacement pump. When a single pump control loop fails, the pressure oil that the parallel valve control loop can provide is several times that of existing schemes. Therefore, compared with existing parallel pump-valve coordinated control schemes, the safety redundancy performance of the pump-valve parallel system in this invention is significantly improved under the same energy efficiency.

[0049] (4) When this invention is used in hybrid vehicles, in the extreme case where the power is completely exhausted and the pump control circuit driven by the electric motor fails, the valve control circuit can be switched to internal combustion engine drive so that the vehicle can retain some steering ability and provide a certain degree of safety for the vehicle. Attached Figure Description

[0050] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0051] Appendix Figure 1 This is a schematic diagram of the steering execution module of the steering control system in an embodiment of the present invention;

[0052] Appendix Figure 2 This is a schematic diagram of the hydraulic principle of the steering control system in an embodiment of the present invention;

[0053] Appendix Figure 3 This is a schematic diagram of the mechanism connection of the steering control system in an embodiment of the present invention;

[0054] Appendix Figure 4 This is a three-dimensional schematic diagram of the steering control system in an embodiment of the present invention;

[0055] Appendix Figure 5This is a schematic diagram of the trajectory tracking control simulation effect in an embodiment of the present invention (a in the figure is the tracking curve of the trajectory tracking control simulation test, and b is the trajectory deviation of the trajectory tracking control simulation test).

[0056] Appendix Figure 6 This is a schematic diagram of energy consumption simulation effect in an embodiment of the present invention;

[0057] Appendix Figure 7 This is a schematic diagram of the control calculation method of the feedforward control and the corresponding parameters of the related equations at the trapezoidal mechanism when the steering actuator of the steering control system forms a trapezoidal mechanism in an embodiment of the present invention.

[0058] In the diagram: 1-oil tank; 2-servo pump unit; 3-fixed displacement pump; 4-relief valve; 5-solenoid directional valve; 6-electro-hydraulic servo valve; 7-steering power cylinder (left and right steering power cylinders). Detailed Implementation

[0059] A pump-valve parallel steering control system for heavy-duty vehicles, such as Figure 1 As shown, a pair of steering wheels of a heavy vehicle are connected to the steering execution module of a pump-valve parallel steering control system at an angle. The angle is driven by the piston of the power steering cylinder, and there is a unique correspondence between the angle of the angle and the displacement of the power steering cylinder piston. The pump-valve parallel steering control system uses a relational equation to convert the wheel angle control signal into the displacement signal of the power steering cylinder piston, and then converts the piston displacement signal into a flow signal and a control element voltage signal for the feedforward control stage of closed-loop steering operation. Subsequently, it combines feedback control for closed-loop control. Specifically, after the controller of the pump-valve parallel steering control system receives the wheel angle feedback signal measured by the sensor, it compares and calculates with the steering control signal. Combined with the received load pressure signal, it adjusts the flow rate of the hydraulic mechanism pump-valve circuit in real time, outputs the required flow rate and direction of hydraulic oil to the power steering cylinder, controls the displacement of the power steering cylinder piston to control the angle rotation, and makes the steering wheel rotate with the angle to execute steering control, forming precise steering feedback control.

[0060] When the heavy vehicle has two or more pairs of steering wheels for steering control, the heavy vehicle uses multiple pump-valve parallel steering control systems to perform combined control of the steering process. Each pair of steering wheels is connected at an angle to a corresponding pump-valve parallel steering control system steering execution module.

[0061] The hydraulic mechanism of a pump-valve parallel steering control system includes a controller, pump control circuit, valve control circuit, steering actuator module, etc. Figure 2 and Figure 3 As shown;

[0062] The pump control circuit includes a servo pump unit (composed of a fixed displacement pump and a servo motor) responsible for flow control, a directional valve responsible for flow direction control, and an overflow valve component responsible for unloading and safety assurance.

[0063] The valve control circuit includes a metering pump and motor responsible for providing flow, a flow divider responsible for distributing the metering pump flow to multiple systems, an electro-hydraulic servo valve responsible for flow and direction control, and an overflow valve element responsible for pressure control.

[0064] The steering execution module includes a left steering assist cylinder and a right steering assist cylinder connected in parallel, as well as a trapezoidal steering mechanism controlled by it; the trapezoidal steering mechanism is a hinged four-bar linkage with one degree of freedom consisting of an axle frame, two steering angles and a long shaft, and the cylinder bodies and extension rods of the left and right steering assist cylinders are connected to the frame and the left and right angles respectively through hinges;

[0065] The pump control circuit, valve control circuit, and steering actuator are connected via parallel valve blocks and pipelines.

[0066] In the pump-valve parallel steering control system, the pump control circuit and the valve control circuit are two control circuits with independent power components and control components. When one circuit fails, the other circuit can work normally, so that the pump-valve parallel steering control system can maintain a certain emergency control capability and provide a certain safety redundancy.

[0067] When the heavy-duty vehicle is a hybrid vehicle, the power system of the vehicle needs to reserve a portion of the power to the pump control circuit to ensure the normal operation of the steering system when distributing energy.

[0068] In the extreme case where the hybrid vehicle's power is completely depleted and the pump control circuit driven by the electric motor in the pump-valve parallel steering control system fails, the valve control circuit of the pump-valve parallel steering control system switches to the internal combustion engine drive of the hybrid vehicle, so that the hybrid vehicle retains some steering ability and provides a certain degree of safety for the vehicle.

[0069] When the hydraulic mechanism of the pump-valve parallel steering control system is working, most of the pressure oil is provided by the high-efficiency pump control circuit to improve the system's energy efficiency. The flow rate of the valve control circuit is supplemented on the basis of the pump control flow rate to improve the dynamic control accuracy of the pump-valve parallel steering control system. The flow rate of the valve control circuit is reduced as much as possible while ensuring the valve control accuracy, so as to take into account the advantages of the high energy efficiency of the pump control circuit and the high dynamics of the valve control circuit.

[0070] Considering the safety redundancy in case of pump control circuit failure, the upper limit of the flow rate that the valve control circuit can provide cannot be too low. Therefore, the flow rate of the fixed displacement pump and the rated flow rate of the servo valve cannot be set too small. When used for multi-axle control of heavy vehicles, the valve control circuits of multiple pumps and valves in parallel steering control systems that correspond one-to-one with multiple pairs of steering wheels of heavy vehicles share a single fixed displacement pump for oil supply and use a flow divider block to split the flow, so as to maintain a large upper limit of flow output while the normal flow rate of a single valve control circuit is low.

[0071] The working method of the pump-valve parallel steering control system for heavy vehicles uses the above-described pump-valve parallel steering control system for heavy vehicles. When the pump-valve parallel steering control system is working, it first converts the steering angle control signal used for steering operation of heavy vehicles into the total flow signal of the hydraulic mechanism of the pump-valve parallel steering control system through the relationship equation between the piston displacement of the steering power cylinder and the wheel angle. Then, based on the total flow signal, the pump control loop performs feedforward control. Finally, based on the deviation between the steering angle control signal and the actual steering angle, the pump control loop and the valve control loop jointly perform PID control to form a closed-loop control.

[0072] When the pump-valve parallel steering control system is working, the wheel rotation angle is measured by the angular displacement sensor installed at the bend.

[0073] like Figure 7 As shown, the derivation process of the equation relating the steering assist cylinder piston displacement and the wheel rotation angle is as follows:

[0074] First, the relationship between the steering angles of the left and right wheels in a pair of steering wheels (measured by an angular displacement sensor installed at the corner) is derived using the following formula:

[0075] Formula 1;

[0076] In the formula, α and β are the steering angles of the left and right tires, respectively; m is the length of the steering angle; L is the length of the tie rod in the pair of steering wheels; γ is the angle at which the steering knuckle arm intersects the axle; B is the distance between the kingpins of the two steering knuckle arms at the axle where the pair of steering wheels are located; and k is the distance from the kingpin of the left knuckle arm to the end of the right knuckle arm.

[0077] Next, the piston displacement x of the left and right power steering cylinders is adjusted. L and x R The left and right wheel rotation angles are used to indicate:

[0078] Formula 2;

[0079] In the formula, n is the distance between the hinge connecting the axle frame and the hinge connecting the power steering cylinder extension rod at the steering angle;

[0080] Then, the flow rate Q required for vehicle steering is calculated by taking the derivative of the power steering cylinder piston displacement as the velocity:

[0081] Formula 3;

[0082] In the formula, A and a are the areas of the rodless chamber and the rod chamber of the power steering cylinder, respectively, and the symbols represent the control direction of the servo valve and the directional valve.

[0083] The specific method for calculating the control voltage of feedforward control is as follows: Match the output flow of the hydraulic system to the flow required for steering by the steering actuator module. Utilizing the relationship between the hydraulic mechanism's output flow and the control voltage, and based on the set distribution ratio (the feedforward flow is mainly provided by the pump control circuit to improve energy efficiency), the required feedforward control signal is calculated in reverse.

[0084] Formula 4;

[0085] In the formula, q p and q v D represents the flow rates of the pump-controlled and valve-controlled circuits, respectively. p For pump displacement; k m u1 and u2 are the speed gain and control voltage of the servo motor, respectively; C d ω is the flow coefficient; u2 is the valve opening gain; ρ is the valve core control voltage; p is the oil density. p p1 is the pump source pressure, and p2 is the load chamber pressure.

[0086] The derivation of the control equations for PID feedback control is as follows:

[0087] First, based on the desired rotation angle control signal β d The control deviation e is calculated using the actual feedback signal β of the turning angle:

[0088] Formula 5;

[0089] The PID controller is as follows:

[0090] Formula 6;

[0091] In the formula, K p K is the proportionality coefficient. i K is the integral coefficient. d is the differential coefficient.

[0092] The PID feedback control signal is derived using Formula 4. The feedback control is mainly performed by the valve control loop to improve the system control accuracy of the pump-valve parallel steering control system.

[0093] Example:

[0094] This example is mainly used for control. Figure 1 The diagram shows a heavy-duty vehicle steering wheelset. In this structure, the axle frame, two hinged corners, and the main shaft form a hinged four-bar trapezoidal steering mechanism with one degree of freedom. The wheel rotates with the hinged corners, and there is a unique correspondence between the corner rotation angle and the steering assist cylinder piston displacement. Therefore, a relationship equation between the steering assist cylinder piston displacement and the wheel rotation angle can be established. This invention utilizes this relationship equation to control the steering assist cylinder piston displacement by controlling the magnitude and direction of the system's output flow, thereby indirectly controlling the wheel steering.

[0095] During operation, the wheel angle control signal is first converted into a steering assist cylinder piston displacement signal using relational equations. Then, the piston displacement signal is converted into a flow signal and a control element voltage signal for feedforward control. After receiving the wheel angle feedback signal, the controller compares and calculates it with the control signal. Combined with the received load pressure signal, the controller adjusts the pump valve circuit flow in real time to perform precise closed-loop feedback control.

[0096] This example primarily applies to heavy-duty multi-axle vehicles, which typically have two or more pairs of steering wheels for steering control, while this system only controls one pair of steering wheels. Therefore, in practical applications, multiple systems may be needed for combined control.

[0097] This system consists of a controller, a pump control circuit, a valve control circuit, a steering actuator module, etc. Figure 2 and Figure 3 As shown. The pump control circuit includes a servo pump unit (composed of a fixed displacement pump and a servo motor) responsible for flow control, a directional valve responsible for flow direction control, and a relief valve responsible for unloading and safety. The valve control circuit includes a fixed displacement pump and motor responsible for providing flow, a flow divider block responsible for distributing the fixed displacement pump flow to multiple systems, an electro-hydraulic servo valve responsible for flow and direction control, and a relief valve responsible for pressure control. The steering actuation module includes two parallel power steering cylinders that act as actuators in the hydraulic system and a trapezoidal steering mechanism controlled by them. The pump control circuit, valve control circuit, and steering actuation module are connected through parallel valve blocks and pipelines.

[0098] In this system, the majority of the pressurized oil is supplied by the highly efficient pump-controlled circuit to improve system efficiency. The flow rate from the valve-controlled circuit is supplemented by the pump-controlled flow rate to enhance dynamic accuracy. The flow rate of the valve-controlled circuit is minimized as much as possible while ensuring valve control accuracy, thus balancing the advantages of both the high efficiency of the pump-controlled circuit and the high dynamic performance of the valve-controlled circuit. Considering safety redundancy in case of pump-controlled circuit failure, the upper limit of the flow rate provided by the valve-controlled circuit cannot be too low. Therefore, the fixed displacement pump flow rate and the rated flow rate of the servo valve cannot be set too low. Furthermore, when used for multi-axis control of heavy vehicles, multiple systems will share a single fixed displacement pump and use a flow divider to split the flow, maintaining a large upper limit of flow output while allowing for a lower flow rate in a single valve-controlled circuit.

[0099] When the system is working, the steering angle control signal is first converted into a total flow signal by the relationship equation between the piston displacement of the power steering cylinder and the wheel angle. Then, the pump control circuit performs feedforward control based on the flow signal. Finally, the pump control circuit and the valve control circuit jointly perform PID control based on the deviation between the steering angle control signal and the actual steering angle.

[0100] Figure 4 The simulation results demonstrate the control performance of a single pump control system, a single valve control system, and the pump-valve parallel system of the present invention under the same control method and controller parameters. The RMSE value of the pump control system is 0.7557°, the RMSE value of the valve control system is 0.08087°, and the RMSE value of the pump-valve parallel system is 0.2145°.

[0101] Figure 5 The simulated control energy consumption of three control systems is shown. The average energy consumption of the pump control system is 358.8W, the average energy consumption of the valve control system is 6000W, and the average energy consumption of the parallel system is 1180W.

[0102] Simulation results show that the pump-valve parallel steering control system designed in this invention is slightly inferior to the valve control system in terms of control accuracy, but far superior to the pump control system. In terms of energy consumption, it is slightly higher than the pump control system, but far lower than the valve control system, thus achieving a balance between high precision and high energy efficiency.

Claims

1. A pump-valve parallel steering control system for heavy-duty vehicles, characterized in that: The heavy vehicle's pair of steering wheels are connected to the steering execution module of the pump-valve parallel steering control system at an angle. The angle is driven by the piston of the power steering cylinder, and there is a unique correspondence between the angle of the angle and the displacement of the power steering cylinder piston. The pump-valve parallel steering control system first uses a relational equation to convert the wheel angle control signal into the displacement signal of the power steering cylinder piston, and then converts the piston displacement signal into a flow signal and a control element voltage signal for the feedforward control stage of closed-loop steering operation. Subsequently, it combines feedback control for closed-loop control. Specifically, after the controller of the pump-valve parallel steering control system receives the wheel angle feedback signal measured by the sensor, it compares and calculates with the steering control signal. Combined with the received load pressure signal, it adjusts the flow rate of the hydraulic mechanism pump-valve circuit in real time, and outputs the required flow rate and direction of hydraulic oil to the power steering cylinder to control the displacement of the power steering cylinder piston to control the angle rotation, so that the steering wheel rotates with the angle to execute steering control, forming a closed-loop steering feedback control. The hydraulic mechanism of the pump-valve parallel steering control system includes a controller, a pump control circuit, a valve control circuit, and a steering execution module; The pump control circuit includes a servo pump unit responsible for flow control, a directional valve responsible for flow direction control, and an overflow valve component responsible for unloading and safety assurance. The valve control circuit includes a metering pump and motor responsible for providing flow, a flow divider responsible for distributing the metering pump flow to multiple systems, an electro-hydraulic servo valve responsible for flow and direction control, and an overflow valve element responsible for pressure control. The steering actuation module includes a left steering assist cylinder and a right steering assist cylinder connected in parallel, as well as a trapezoidal steering mechanism controlled by them; The trapezoidal steering mechanism is a hinged four-bar linkage with one degree of freedom, consisting of an axle square frame, two steering angles, and a long shaft. The cylinder bodies and extension rods of the left and right steering assist cylinders are connected to the square frame and the left and right angles respectively via hinges. The pump control circuit, valve control circuit, and steering actuator are connected via parallel valve blocks and pipelines; In the pump-valve parallel steering control system, the pump control circuit and the valve control circuit are two control circuits with independent power components and control components. When one circuit fails, the other circuit can work normally, so that the pump-valve parallel steering control system can maintain emergency control capability and provide safety redundancy.

2. The pump-valve parallel steering control system for heavy vehicles according to claim 1, characterized in that: When the heavy vehicle has two or more pairs of steering wheels for steering control, the heavy vehicle uses multiple pump-valve parallel steering control systems to perform combined control of the steering process. Each pair of steering wheels is connected at an angle to a corresponding pump-valve parallel steering control system steering execution module.

3. A pump-valve parallel steering control system for heavy-duty vehicles according to claim 1, characterized in that: When the heavy-duty vehicle is a hybrid vehicle, the power system of the vehicle reserves the necessary power for the steering system to ensure that the steering system works normally when distributing energy. When the hybrid vehicle's power is completely depleted and the pump control circuit driven by the electric motor in the pump-valve parallel steering control system fails, the valve control circuit of the pump-valve parallel steering control system switches to the internal combustion engine drive of the hybrid vehicle, so that the hybrid vehicle retains some steering ability and provides safety assurance for the vehicle.

4. A pump-valve parallel steering control system for heavy-duty vehicles according to claim 1, characterized in that: When the hydraulic mechanism of the pump-valve parallel steering control system is working, most of the pressure oil is provided by the high-efficiency pump control circuit to improve the system's energy efficiency. The flow rate of the valve control circuit is supplemented on the basis of the pump control flow rate to improve the dynamic control accuracy of the pump-valve parallel steering control system. While ensuring the valve control accuracy, the flow rate of the valve control circuit is reduced as much as possible to take into account the advantages of the high energy efficiency of the pump control circuit and the high dynamics of the valve control circuit. When used for multi-axle control of heavy vehicles, the valve control circuit of the parallel steering control system, which controls multiple pairs of steering wheels of heavy vehicles one-to-one, shares a fixed-displacement pump for oil supply and uses a flow divider to split the flow, so as to maintain a large flow output limit while the normal flow of a single valve control circuit is low.

5. A method for operating a pump-valve parallel steering control system for heavy-duty vehicles, using the pump-valve parallel steering control system for heavy-duty vehicles according to claim 1, characterized in that: When the pump-valve parallel steering control system is working, it first converts the steering angle control signal used for steering operation of heavy vehicles into the total flow signal of the hydraulic mechanism of the pump-valve parallel steering control system through the relationship equation between the piston displacement of the steering power cylinder and the wheel angle. Then, based on the total flow signal, the pump control loop performs feedforward control. Finally, based on the deviation between the steering angle control signal and the actual steering angle, the pump control loop and the valve control loop jointly perform PID control to form a closed-loop control. When the pump-valve parallel steering control system is working, the wheel rotation angle is measured by the angular displacement sensor installed at the bend.

6. The operating method of the pump-valve parallel steering control system for heavy vehicles according to claim 5, characterized in that: The derivation process of the equation relating the power steering cylinder piston displacement and the wheel rotation angle is as follows: First, we derive the relationship between the steering angles of the left and right wheels in a pair of steering wheels. The formula is: Official 1; In the formula, α and β are the steering angles of the left and right tires, respectively; m is the length of the steering angle; L is the length of the tie rod in the pair of steering wheels; γ is the angle at which the steering knuckle arm intersects the axle; B is the distance between the kingpins of the two steering knuckle arms at the axle where the pair of steering wheels are located; k is the distance from the kingpin of the left knuckle arm to the end of the right knuckle arm. Next, the piston displacement x of the left and right power steering cylinders is adjusted. L and x R The left and right wheel rotation angles are used to indicate: Official 2; In the formula, n is the distance between the hinge connecting the axle frame and the hinge connecting the power steering cylinder extension rod at the steering angle; Then, the flow rate Q required for vehicle steering is calculated by taking the derivative of the power steering cylinder piston displacement as the velocity: Official 3; In the formula, A and a are the areas of the rodless chamber and the rod chamber of the power steering cylinder, respectively, and the symbols represent the control direction of the servo valve and the directional valve.

7. The operating method of the pump-valve parallel steering control system for heavy vehicles according to claim 6, characterized in that: The specific method for calculating the control voltage of feedforward control is as follows: Match the output flow of the hydraulic system to the flow required by the steering actuator module. Utilize the relationship between the hydraulic mechanism's output flow and the control voltage, and calculate the required feedforward control signal based on the set distribution ratio. The formula is: Official 4; In the formula, q p and q v The flow rates D for the pump control circuit and the valve control circuit, respectively. p k is the pump displacement. m u1 and u2 are the speed gain and control voltage of the servo motor, respectively; C d ω is the flow coefficient; u2 is the valve opening gain; ρ is the valve core control voltage; p is the oil density. p p1 is the pump source pressure, and p1 is the load chamber pressure.

8. The operating method of the pump-valve parallel steering control system for heavy vehicles according to claim 7, characterized in that: The derivation of the control equations for PID feedback control is as follows: First, based on the desired rotation angle control signal β d The control deviation e is calculated using the actual feedback signal β of the turning angle: Official 5; The PID controller is as follows: Official 6; In the formula, K p K is the proportionality coefficient. i K is the integral coefficient. d These are the differential coefficients; Formula 4 is used to derive the PID feedback control signal. When it is necessary to improve the system control accuracy of the pump-valve parallel steering control system, the feedback control is dominated by the valve control loop.

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