Pump-controlled main drive tie rod auxiliary valve-controlled electro-hydraulic steering system and control method

Abstract

The application provides an electro-hydraulic steering system and a control method, which are pump-controlled and controlled by a cross rod auxiliary valve, and comprise a variable-speed pump-driven double steering assistance cylinder main drive system, a cross rod auxiliary valve control system and an electronic control system; the variable-speed pump-driven double steering assistance cylinder main drive system is a pump control system, controls left and right wheel steering assistance cylinders through a servo motor pump unit and a steering assistance cylinder valve group, and controls the cross rod auxiliary valve control system by distributing flow; the cross rod auxiliary valve control system is a valve control system, controls a large and small cavity cross rod cylinder through a cross rod cylinder valve group and a locking device, and assists the main drive system to control left and right wheel angles; the electronic control system outputs a control instruction to control left and right wheel angles in real time according to an input target angle signal and signals of left and right wheel angle sensors. The technical scheme can guarantee a pure rolling steering effect of the system and improve the safety of the system when it is applied to high-speed vehicles.

Description

Technical Field

[0001] This invention relates to the field of automotive steering technology, and in particular to a pump-controlled main drive tie rod auxiliary valve-controlled electro-hydraulic steering system and its control method. Background Technology

[0002] With the development of my country's civil infrastructure construction and national defense modernization, the market demand for multi-axle vehicles has increased dramatically, leading to the rapid development of multi-axle vehicle technology. However, in both military and civilian industries, multi-axle vehicles operate under harsh conditions, requiring multi-axle steering systems to simultaneously adapt to all-terrain driving, multiple steering modes, high-load driving capacity, high efficiency, and precision. Electro-hydraulic servo steering systems have become the preferred solution for multi-axle steering systems due to their advantages such as fast dynamic response and high output power. Traditional electro-hydraulic valve-controlled trapezoidal steering systems are single-degree-of-freedom systems that use an engine-driven fixed-displacement pump to provide power and servo proportional valves to control dual steering assist cylinders. This system cannot achieve precise steering of each wheel according to the target turning angle or on-demand power supply to each axle. Furthermore, traditional electro-hydraulic valve-controlled trapezoidal steering systems have complex configurations, high costs, unavoidable overflow and throttling losses, significant energy consumption, and are accompanied by severe heat generation and noise. Therefore, designing a new system configuration is essential to achieve high-precision steering and reduce system energy consumption.

[0003] Existing technical solutions help improve the performance of electro-hydraulic servo steering systems, but still have the following shortcomings:

[0004] 1. As the number of actuators in a multi-axle steering system increases, traditional single-pump / few-pump systems struggle to meet the demands of multiple actuators. While each actuator can achieve high precision using traditional servo valve control, the increased number of actuators makes it impossible for traditional single-pump / few-pump systems to adjust the pump pressure and flow rate according to the needs of each actuator. This leads to energy waste, insufficient working pressure, and unreasonable pressure and flow distribution. Furthermore, heavy-duty multi-axle vehicles exhibit significant differences in the length of the tie rod in the last axle steering mechanism across different steering modes, posing a challenge to multi-mode, high-precision steering under complex conditions. Steering systems with fixed tie rod lengths cannot meet the performance requirements of multi-mode steering.

[0005] 2. The control capability and energy efficiency of the two-degree-of-freedom electro-hydraulic steering system with adjustable transverse cylinder length need to be improved. Although the two-degree-of-freedom electro-hydraulic steering system with adjustable transverse cylinder length can achieve multi-mode switching and take into account both high load and high-precision steering, this method increases the number of actuators, making high-precision steering control under high load more difficult and increasing energy consumption.

[0006] 3. Safety in situations where the tie rod cylinder valve control system fails, preventing the tie rod cylinder from locking itself, needs improvement. When the tie rod cylinder valve control system fails to supply fluid normally due to special reasons, or when there is internal leakage in the hydraulic cylinder or hydraulic lock, the tie rod cylinder cannot lock, which can easily lead to problems such as tire sideslip and loss of steering control, seriously affecting the driving safety of multi-axle vehicles. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a pump-controlled main drive tie rod auxiliary valve-controlled electro-hydraulic steering system and its control method. The steering system includes a main drive system with variable speed pump-driven dual steering assist cylinders and a tie rod auxiliary valve control system. By using the variable speed pump-driven dual steering assist cylinders and the tie rod auxiliary valve control system to perform electro-hydraulic servo composite control on the adjustable trapezoidal steering mechanism of the tie rod, multi-mode, high-precision dynamic steering is achieved while simultaneously saving energy. Preferably, the steering system also includes an externally controlled hydraulic lock and locking device, which can lock the tie rod cylinder and the left and right steering assist cylinders when needed, ensuring the system's pure rolling steering effect and improving its safety when used in high-speed vehicles.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a pump-controlled main drive tie rod auxiliary valve-controlled electro-hydraulic steering system, comprising a variable speed pump-driven dual steering assist cylinder main drive system, a tie rod auxiliary valve control system, and an electronic control system; the variable speed pump-driven dual steering assist cylinder main drive system is a pump control system, which controls the left and right wheel steering assist cylinders through a servo motor pump unit and steering assist cylinder valve group, and diverts a flow to control the tie rod auxiliary valve control system; the tie rod auxiliary valve control system is a valve control system, which controls the large and small chamber tie rod cylinders through tie rod cylinder valve group and locking device, assisting the main drive system in controlling the left and right wheel rotation angles; the electronic control system outputs control commands to control the left and right wheel rotation angles in real time based on the input target rotation angle signal and the signals from the left and right wheel angle sensors.

[0009] In a preferred embodiment: the main drive system of the variable speed pump-driven dual steering power cylinder includes a servo motor pump unit, a flow meter, a steering power cylinder valve group, a left steering power cylinder, and a right steering power cylinder; the first working oil circuit, consisting of the rodless chamber of the left steering power cylinder and the rod chamber of the right steering power cylinder, is connected to the A working oil port of the solenoid directional valve, and the second working oil circuit, consisting of the rod chamber of the left steering power cylinder and the rodless chamber of the right steering power cylinder, is connected to the B working oil port of the solenoid directional valve; the P port of the solenoid directional valve is connected to the oil inlet circuit, and the T port is connected to the oil tank.

[0010] In a preferred embodiment: the servo motor pump unit consists of a servo motor and a fixed displacement pump, serving as the pump source for the main drive system of the variable speed pump-driven dual steering assist cylinder; the pressure and flow rate of the main drive system are controlled by the servo motor pump unit, and the direction is controlled by an electromagnetic reversing valve; the servo motor pump unit adjusts the servo motor speed under the control of the controller to adapt to changes in working pressure and provide flow rate as needed; the main drive system also includes four oil replenishment overflow valve groups, which are connected in series with four working oil circuits respectively; the oil replenishment overflow valve group consists of an overflow valve and a check valve connected in parallel.

[0011] In a preferred embodiment: the tie rod auxiliary valve control system includes a tie rod cylinder valve group, a tie rod cylinder with large and small chambers, and a locking device; the working oil circuit of the large chamber of the tie rod cylinder is connected to port A of the servo proportional valve, and the working oil circuit of the small chamber is connected to port B of the servo proportional valve, forming a third working oil circuit and a fourth working oil circuit respectively; the locking device is located at the small chamber end of the tie rod cylinder; the P port of the servo proportional valve is connected to the oil inlet circuit, and the T port is connected to the oil tank; the tie rod auxiliary valve control system and the main drive system share a pump source.

[0012] In a preferred embodiment: a flow branch is drawn from the main drive system and a servo proportional valve is used to control the tie rod cylinder; the tie rod cylinder with large and small chambers is a double-outlet cylinder with optimized structural parameters; the working areas of the rod chambers on both sides of the tie rod cylinder are not equal, and a locking device is connected to the end cap of the small chamber.

[0013] In a preferred embodiment: a multi-objective optimization method based on genetic algorithm is used to optimize the structural parameters of the large and small cavity tie rod cylinder. Drive power and steering force are selected as optimization objectives, pressure and flow parameters of the tie rod auxiliary valve control system are used as constraints, and the large and small cavity areas, cylinder diameter, rod diameter, and stroke structural parameters are used as optimization parameters. A multi-objective optimization model for the large and small cavity hydraulic cylinder is constructed, as follows:

[0014]

[0015] Where P is the driving power; F is the steering driving force; X1,…,X n Optimized parameters for large and small cavity hydraulic cylinders; These are the minimum and maximum values ​​of the i-th constraint, respectively; Let be the minimum and maximum values ​​of the i-th optimization parameter, respectively. Then, a genetic algorithm is used to perform multi-objective optimization of the structural parameters of the large and small cavity hydraulic cylinders. The fitness function of the genetic algorithm is constructed as follows:

[0016]

[0017] Where, θ iLet be the fitness of the i-th individual; a and b are fitness parameters used to adjust the weights of driving power and steering force in the optimization; P i F i These are the predicted values ​​of the driving power and steering driving force for the i-th individual, respectively; θ i The smaller the value, the smaller the driving power and the greater the steering driving force for that individual.

[0018] In a preferred embodiment: the locking device forms a wedge-shaped lock through a conical locking ring and a conical sleeve, thus forming a mechanical self-locking mechanism; the control port of the locking device is connected to the first reversing ball valve, and when the first reversing ball valve is energized, the locking device and the hydraulic lock work together to make the large and small chamber tie rod cylinder self-locking.

[0019] In a preferred embodiment: the hydraulically controlled check valve and the directional ball valve form an externally controlled hydraulic lock, which are connected in series in port A and port B of the servo proportional valve and the solenoid directional valve, respectively; the first directional ball valve and the second directional ball valve are both two-position three-way valves, and the hydraulic lock is locked when the directional ball valve is energized.

[0020] This invention provides a control method for a pump-controlled main drive tie rod-assisted valve-controlled electro-hydraulic steering system, employing the aforementioned pump-controlled main drive tie rod-assisted valve-controlled electro-hydraulic steering system, comprising the following steps:

[0021] Step S1: The electro-hydraulic servo steering system inputs the left and right target steering angle signals of the controlled steering axle to the controller;

[0022] Step S2: Determine whether it is necessary to lock the large and small chamber tie rod cylinders: if not, skip to step S3; if so, skip to step S8.

[0023] Step S3: The controller uses the target steering angle signals of the left and right wheels as two control targets to control the system;

[0024] Step S4: Detect the actual turning angles of the left and right wheels of the controlled steering axle, and calculate the deviations between the actual turning angles of the left and right wheels and the target turning angles respectively;

[0025] Step S5: Based on the deviation signal between the target rotation angle and the current rotation angle of the left wheel, the controller sends signals to the servo motor and the solenoid directional valve to control their operation; based on the deviation signal between the target rotation angle and the current rotation angle of the right wheel, the controller controls the servo proportional valve to operate.

[0026] Step S6: The servo proportional valve outputs a hydraulic signal to control the extension and retraction of the large and small chamber tie rod cylinders. The servo motor pump unit and the solenoid directional valve together control the extension and retraction of the left and right steering assist cylinders, so that the left or right wheel reaches the target turning angle.

[0027] Step S7: Determine whether the left wheel steering angle deviation signal is greater than the critical steering angle threshold of 0.2°: If it is greater, proceed to step S3; if it is not greater, proceed to step S8.

[0028] Step S8: Set the servo proportional valve to the neutral position, energize the first directional ball valve, and return the pilot oil of the first hydraulic check valve and the second hydraulic check valve to the oil chamber, locking the tie rod cylinder;

[0029] Step S9: In sync with step S8, calculate the deviation between the left and right wheels and the target turning angle;

[0030] Step S10: Based on the deviation between the actual turning angle of the left wheel and the target turning angle, the controller sends command signals to the servo motor and the solenoid directional valve to control the extension and retraction of the left and right steering assist cylinders to achieve the target turning angle;

[0031] In a preferred embodiment: the servo motor changes its speed via a voltage control signal, thereby adjusting the output flow and pressure of the metering pump; angular velocity feedforward-angle feedback control is used to control the solenoid directional valve, with left turn set as positive. The deviation angle between the target and actual steering angle of the left steering wheel is used as the feedback signal, the target angular velocity as the feedforward signal, and the sum of the feedback signal and the feedforward signal as the control signal. The control signal function is as follows:

[0032] U=(θ q -θ s )+ω q

[0033] Where U is the control signal, θ q For the target turning angle, θ s ω is the actual turning angle. q The target angular velocity.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. A pump-controlled main drive / tie bar auxiliary valve-controlled electro-hydraulic steering system is designed based on a two-degree-of-freedom mechanism with adjustable tie rod length, making the system more efficient and energy-saving, and always operating at its optimal performance. A servo motor pump unit consisting of a servo motor and a fixed displacement pump is used as the pump source for each steering shaft. In the main drive system, an electromagnetic directional valve replaces the servo proportional valve in the traditional system, allowing the pressure and flow of the steering system to be directly controlled by the servo motor pump unit, achieving on-demand power supply and making the system more efficient and energy-saving. Simultaneously, the control chamber pressure of the power steering cylinder is directly controlled by the servo motor pump unit, simplifying the system and its pressure control algorithm. Furthermore, a small-flow branch using a servo proportional valve is branched off from the main drive system to control the tie rod auxiliary valve control system, enabling the system to simultaneously control the steering angles of both wheels, meeting constraints under all road conditions and achieving high-precision control of the steering system.

[0036] 2. A novel large and small chamber tie rod servo cylinder is designed to improve the control capability and energy efficiency of the tie rod cylinder, based on the requirements of the pump-controlled main drive / tie rod auxiliary valve-controlled electro-hydraulic steering system. By designing the structural parameters such as the area of ​​the large and small chambers, cylinder diameter, and rod diameter of the tie rod cylinder, the maximum steering driving force and minimum driving power are matched, improving the system's control capability and energy efficiency. Furthermore, by controlling the externally controlled hydraulic lock on the auxiliary branch circuit to lock or unlock the tie rod cylinder, the system achieves multiple mode switching functions, including minimum turning radius controllable tie rod and crab-tied tie rod locking, for the pump-controlled main drive / tie rod auxiliary valve-controlled electro-hydraulic steering system.

[0037] 3. By employing both hydraulic and mechanical self-locking on the large and small cavity tie rod cylinders, the safety of the multi-axle vehicle steering system is ensured. Specifically, while an externally controlled hydraulic lock self-locks the large and small cavity tie rod cylinders, a locking device connected to the small cavity end cap mechanically self-locks the tie rod cylinder, providing dual protection for the tie rod cylinder's self-locking and improving the safety of the steering system. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of a pump-controlled main drive / tie rod auxiliary valve-controlled electro-hydraulic steering system according to a preferred embodiment of the present invention;

[0039] Figure 2 This is a flowchart of a preferred embodiment of the multi-objective optimization design method for a large-cavity tie rod cylinder based on a genetic algorithm.

[0040] Figure 3 This is a schematic diagram of the locking device of the large and small cavity cross tie rod cylinder according to a preferred embodiment of the present invention;

[0041] Figure 4 This is a flowchart of the steering control method of the system involved in the preferred embodiment of the present invention;

[0042] In the diagram: 1. Oil tank; 2. Shut-off valve; 3. Servo motor; 4. Fixed displacement pump; 5. Check valve; 6. Overflow valve; 7. Flow meter; 8. Servo proportional valve; 9. First directional ball valve; 10. First hydraulically controlled check valve; 11. Second hydraulically controlled check valve; 12. First replenishing overflow valve assembly; 13. Second replenishing overflow valve assembly; 14. Tie rod cylinder valve assembly; 15. Left steering wheel; 16. Frame; 17. Left angle sensor; 18. Left steering power cylinder; 19. Locking device; 20. Large and small chamber tie rod cylinder; 21. Right steering power cylinder; 22. Right steering wheel; 3. Right angle sensor; 24. Controller; 25. Third hydraulic check valve; 26. Fourth hydraulic check valve; 27. Power steering cylinder valve assembly; 28. Third replenishing overflow valve assembly; 29. ​​Fourth replenishing overflow valve assembly; 30. Solenoid directional valve; 31. Second directional ball valve; 32. Shut-off valve; 33. Filter; 34. Check valve; 35. Filter; 36. Servo motor pump unit; 37. Piston rod; 38. Sealing ring; 39. Locking device mounting base; 40. Locking device oil inlet; 41. Conical locking ring; 42. Spring; 43. Small cavity end cap. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0044] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0045] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0046] A pump-controlled main drive tie rod auxiliary valve-controlled electro-hydraulic steering system, referenced Figures 1 to 4The system includes a main drive system for a variable-speed pump-driven dual steering power cylinder, a tie rod auxiliary valve control system, and an electronic control system. The main drive system for the variable-speed pump-driven dual steering power cylinder includes an oil tank 1, a servo motor pump unit 36, a check valve 5, a filter 33, a flow meter 7, a steering power cylinder valve group 27, a left steering power cylinder 18, and a right steering power cylinder 21. A first working oil circuit R1, consisting of the rodless chamber of the left steering power cylinder 18 and the rod chamber of the right steering power cylinder 21, is connected to the A working port of the solenoid directional valve 30. A second working oil circuit R2, consisting of the rod chamber of the left steering power cylinder 18 and the rodless chamber of the right steering power cylinder 21, is connected to the B working port of the solenoid directional valve 30. The tie rod auxiliary valve control system includes a tie rod cylinder valve group 14, a large and small chamber tie rod cylinder 20, and a locking device 19. The large and small chamber tie rod... The large chamber working oil circuit of the lever cylinder 20 is connected to port A of the servo proportional valve 8, and the small chamber working oil circuit is connected to port B of the servo proportional valve 8, forming the third working oil circuit R3 and the fourth working oil circuit R4 respectively; the P port of the servo proportional valve 8 and the solenoid directional valve 30 are both connected to the oil inlet circuit, and the T port is connected to the oil tank; the electronic control system includes a controller 24, a servo motor 3, a left wheel angle sensor 17, and a right wheel angle sensor 23; the controller is connected to the servo motor 3, the solenoid directional valve 30, the servo proportional valve 8, the first directional ball valve 9, the second directional ball valve 31, and the left and right wheel angle sensors respectively. The controller is used to calculate the deviation between the target turning angle and the actual turning angle of the left and right steering wheels, and send real-time control signals to the servo motor 3, the solenoid directional valve 30, the servo proportional valve 8, and the directional ball valve according to the calculation results.

[0047] The main drive system of the variable speed pump-driven dual steering power cylinder uses a servo motor pump unit as the pump source. This unit consists of a servo motor 3 and a fixed displacement pump 4. The pressure and flow rate of the main drive system are controlled by the servo motor pump unit, and the direction is controlled by the electromagnetic reversing valve 30. Under the control of the controller 24, the servo motor pump unit adjusts the speed of the servo motor 3 to adapt to changes in working pressure and provide flow rate as needed.

[0048] The main drive system controls the left and right steering cylinders to achieve left and right wheel steering. The tie rod auxiliary valve control system controls the extension and retraction of the tie rod cylinder to assist in steering angle control. The tie rod auxiliary valve control system shares a pump source with the main drive system, and a branch flow is drawn from the main drive system and a servo proportional valve is used to control the tie rod cylinder.

[0049] The large and small cavity tie rod cylinder 20 is an optimized double rod cylinder, and the working areas of the rod cavities on both sides of the tie rod cylinder are not equal.

[0050] The structural parameters of the large and small cavity tie rod cylinder 20 are optimized using a multi-objective optimization method based on a genetic algorithm. Driving power and steering driving force are selected as optimization objectives, while parameters such as pressure and flow rate of the tie rod auxiliary valve control system are used as constraints. Structural parameters such as the area of ​​the large and small cavities, cylinder diameter, rod diameter, and stroke are used as optimization parameters. A multi-objective optimization model for the large and small cavity hydraulic cylinder is constructed as follows:

[0051]

[0052] Where P is the driving power; F is the steering driving force; X1,…,X n Optimized parameters for large and small cavity hydraulic cylinders; These are the minimum and maximum values ​​of the i-th constraint, respectively; These are the minimum and maximum values ​​of the i-th optimization parameter, respectively;

[0053] A genetic algorithm is used to perform multi-objective optimization of the structural parameters of large and small cavity hydraulic cylinders. Within the range of optimization parameter values, n individuals are generated as a population, and the fitness of each individual in the population is calculated. The individuals are then sorted according to their fitness, and individuals with low fitness are eliminated, while those with high fitness are retained. The retained individuals are then crossovered and mutated to generate a new population. Crossover is achieved by exchanging a certain optimization parameter between two individuals, and mutation is achieved by changing the random optimization parameter of a random individual. The fitness function of the genetic algorithm is constructed as follows:

[0054]

[0055] Where, θ i Let be the fitness of the i-th individual; a and b are fitness parameters used to adjust the weights of driving power and steering force in the optimization; P i F i These are the predicted values ​​of the driving power and steering driving force for the i-th individual, respectively; θ i The smaller the value, the smaller the driving power and the greater the steering driving force for that individual.

[0056] A locking device 19 is attached to the end cap of the small cavity of the large and small cavity tie rod cylinder 20. A wedge-shaped locking mechanism, formed by the conical locking ring 41 and the locking device mounting seat 39, completes the mechanical self-locking of the tie rod cylinder. The oil inlet 40 of the locking device is connected to the first reversing ball valve 9. When the first reversing ball valve 9 is energized, the large and small cavity tie rod cylinder 20 achieves mechanical self-locking. The structure of the locking device is as follows: Figure 3 As shown.

[0057] When self-locking is required, the first reversing ball valve 9 is energized, the oil inlet 40 of the locking device is depressurized, and the conical locking ring 41 is pressed tight under the action of the spring 42, which increases the friction between the conical locking ring 41 and the piston rod 37. At the same time, since the cross rod cylinder is constantly under tension, it also causes the conical locking ring 41 to lock until the piston rod is locked to complete the mechanical self-locking.

[0058] When unlocking is required, the first reversing ball valve 9 is de-energized, and pressurized oil is introduced into the oil inlet 40 of the locking device. The hydraulic oil squeezes the conical locking ring 41, causing the piston rod 37 to be released and the unlocking is completed.

[0059] Preferably, the system also includes four replenishing overflow valve groups, which are connected in series with the four working oil circuits respectively; the replenishing overflow valve group consists of an overflow valve and a check valve connected in parallel.

[0060] Preferably, the hydraulically controlled check valve and the directional ball valve form an externally controlled hydraulic lock, which are connected in series in the AB ports of the servo proportional valve 8 and the solenoid directional valve 30, respectively; the first directional ball valve 9 and the second directional ball valve 31 are both two-position three-way valves, and the hydraulic lock is locked when the ball valve is energized.

[0061] Preferably, the servo motor 3 changes its speed via a voltage control signal, thereby adjusting the output flow and pressure of the metering pump 4; and feedforward compensation is used to improve the response speed of the electromagnetic directional valve 30.

[0062] Figure 4 This is a flowchart of the steering control method of the system involved in this invention.

[0063] Includes the following steps:

[0064] Step S1: The electro-hydraulic servo steering system inputs the left and right target steering angle signals of the controlled steering axle to the controller;

[0065] Step S2: Determine whether it is necessary to lock the large and small chamber tie rod cylinders: if not, skip to step S3; if so, skip to step S8.

[0066] Step S3: The controller uses the target steering angle signals of the left and right wheels as two control targets to control the system;

[0067] Step S4: Detect the actual turning angles of the left and right wheels of the controlled steering axle, and calculate the deviations between the actual turning angles of the left and right wheels and the target turning angles respectively;

[0068] Step S5: Based on the deviation signal between the target rotation angle and the current rotation angle of the left wheel, the controller sends signals to the servo motor and the solenoid directional valve to control their operation; based on the deviation signal between the target rotation angle and the current rotation angle of the right wheel, the controller controls the servo proportional valve to operate.

[0069] Step S6: The servo proportional valve outputs a hydraulic signal to control the extension and retraction of the large and small chamber tie rod cylinders. The servo motor pump unit and the solenoid directional valve together control the extension and retraction of the left and right steering assist cylinders, so that the left or right wheel reaches the target turning angle.

[0070] Step S7: Determine whether the left wheel steering angle deviation signal is greater than the critical steering angle threshold of 0.2°: If it is greater, proceed to step S3; if it is not greater, proceed to step S8.

[0071] Step S8: Set the servo proportional valve to the neutral position, energize the first directional ball valve, and return the pilot oil of the first hydraulic check valve and the second hydraulic check valve to the oil chamber, locking the tie rod cylinder;

[0072] Step S9: In sync with step S8, calculate the deviation between the left and right wheels and the target turning angle;

[0073] Step S10: Based on the deviation between the actual turning angle of the left wheel and the target turning angle, the controller sends command signals to the servo motor and the solenoid directional valve to control the extension and retraction of the left and right steering assist cylinders to achieve the target turning angle;

[0074] Preferably, angular velocity feedforward-angle feedback control is used to improve the switching accuracy of the electromagnetic directional valve. Left turn is set as positive. The deviation angle between the target and actual turning angle of the left steering wheel is used as the feedback signal, and the target angular velocity is used as the feedforward signal. The sum of the feedback and feedforward signals is used as the control signal. When the control signal is greater than 0, the directional valve operates in the left position; when the control signal is equal to 0, the directional valve operates in the middle position; and when the control signal is less than 0, the directional valve operates in the right position. The control signal function is as follows:

[0075] U=(θ q -θ s )+ω q

[0076] Where U is the control signal, θ q For the target turning angle, θ s ω is the actual turning angle. q The target angular velocity.

[0077] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. An electro-hydraulic steering system with pump-controlled main drive tie rod assisted valve control, characterized in that: The main drive system of the variable speed pump driven double steering assist cylinder, the cross rod auxiliary valve control system and the electronic control system are included; the main drive system of the variable speed pump driven double steering assist cylinder is a pump control system, the left and right wheel steering assist cylinders are controlled through the servo motor pump unit and the steering assist cylinder valve group, and a branch flow is branched out to control the cross rod auxiliary valve control system; the cross rod auxiliary valve control system is a valve control system, the large and small cavity cross rod cylinders are controlled through the cross rod cylinder valve group and the locking device, and the main drive system is assisted to control the left and right wheel angles; the electronic control system outputs control instructions to control the left and right wheel angles in real time according to the target angle signal and the signals of the left and right wheel angle sensors; The main drive system of the variable speed pump driven double steering assist cylinder includes a servo motor pump unit, a flowmeter, a steering assist cylinder valve group, a left steering assist cylinder and a right steering assist cylinder; a first working oil circuit composed of the rodless cavity of the left steering assist cylinder and the rod cavity of the right steering assist cylinder is connected with the A working oil port of the electromagnetic reversing valve, and a second working oil circuit composed of the rod cavity of the left steering assist cylinder and the rodless cavity of the right steering assist cylinder is connected with the B working oil port of the electromagnetic reversing valve; the P ports of the electromagnetic reversing valve are connected with the oil inlet circuit, and the T ports are connected with the oil tank; The servo motor pump unit is composed of a servo motor and a constant displacement pump, and serves as the pump source of the main drive system of the variable speed pump driven double steering assist cylinder; the pressure and flow of the main drive system are controlled by the servo motor pump unit, and the direction is controlled by the electromagnetic reversing valve; the servo motor pump unit adjusts the speed of the servo motor under the control of the controller, so as to adapt to the change of working pressure and provide flow as needed; the main drive system further includes four oil supplement overflow valves which are connected in series with the four working oil circuits; the oil supplement overflow valve group is composed of an overflow valve and a check valve in parallel; The cross rod auxiliary valve control system includes a cross rod cylinder valve group, a large and small cavity cross rod cylinder and a locking device; the large cavity working oil circuit of the large and small cavity cross rod cylinder is connected with the A port of the servo proportional valve, and the small cavity working oil circuit is connected with the B port of the servo proportional valve, thereby forming a third working oil circuit and a fourth working oil circuit; the locking device is located at the small cavity end of the large and small cavity cross rod cylinder; the P ports of the servo proportional valve are connected with the oil inlet circuit, and the T ports are connected with the oil tank; the cross rod auxiliary valve control system shares a pump source with the main drive system; A branch flow is branched out from the main drive system, and the servo proportional valve is used to control the cross rod cylinder; the large and small cavity cross rod cylinder is a double rod cylinder which is optimized in structure parameters; the working areas of the rod cavities on both sides of the cross rod cylinder are not equal, and the locking device is connected to the small cavity end cap; A multi-objective optimization method based on genetic algorithm is used to optimize the structure parameters of the large and small cavity cross rod cylinder; the driving power and the steering driving force are selected as the optimization objectives, the pressure and flow parameters of the cross rod auxiliary valve control system are selected as the constraint conditions, the large and small cavity areas, the cylinder diameter, the rod diameter and the stroke structure parameters are selected as the optimization parameters, a multi-objective optimization model of the large and small cavity hydraulic cylinder is constructed, and the multi-objective optimization model of the large and small cavity hydraulic cylinder is as follows: Wherein, P is the driving power; F is the steering driving force; are the optimization parameters of the size cavity hydraulic cylinder; , are the minimum and maximum values of the i th constraint condition respectively; , are the minimum and maximum values of the i th optimization parameter respectively, and the genetic algorithm is used to carry out multi-objective optimization on the structure parameters of the size cavity hydraulic cylinder. The fitness function of the genetic algorithm is constructed as follows: wherein, fitness of the ith individual; a, b are fitness parameters for adjusting the weight of driving power and steering driving force in optimization; , are the predicted values of driving power and steering driving force of the ith individual, respectively; the The smaller the value is, the smaller the driving power and the larger the steering driving force corresponding to the individual are. The locking device is formed into wedge-shaped locking by a conical locking ring and a conical sleeve, and forms mechanical self-locking; the locking device control port is connected with the first reversing ball valve, the first reversing ball valve is powered, and the locking device and the hydraulic lock jointly act to lock the size cavity cross rod cylinder.

2. The pump-controlled, master-link-assisted, valve-controlled electro-hydraulic steering system of claim 1, wherein: The hydraulic control one-way valve and the reversing ball valve form an externally controlled hydraulic lock, and are connected in series at the A port and the B port of the servo proportional valve and the electromagnetic reversing valve; the first reversing ball valve and the second reversing ball valve are both two-position three-way valves, and the reversing ball valve is powered to lock the hydraulic lock.

3. Control method of an electro-hydraulic steering system with pump-controlled main drive tie rod assisted valve control, characterized in that The pump-controlled main drive cross rod auxiliary valve-controlled electro-hydraulic steering system of the above-mentioned claim 1 or 2 comprises the following steps: Step S1: the electro-hydraulic servo steering system inputs the left and right target turning angle signals of the controlled steering bridge to the controller; Step S2: it is judged whether the size cavity cross rod cylinder needs to be locked: if not, jump to step S3; if yes, jump to step S8; Step S3: the controller controls the left and right target turning angle signals of the wheels as two control targets to control the system; Step S4: the actual turning angles of the left and right wheels of the controlled steering bridge are detected, and the deviations between the actual turning angles and the target turning angles of the left and right wheels are calculated respectively; Step S5: according to the deviation signal between the target turning angle and the current turning angle of the left wheel, the controller sends a signal to control the servo motor and the electromagnetic reversing valve; according to the deviation signal between the target turning angle and the current turning angle of the right wheel, the servo proportional valve is controlled to work; Step S6: the servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the size cavity cross rod cylinder, and the servo motor pump unit and the electromagnetic reversing valve together control the expansion and contraction of the left and right steering assistance cylinders, so that the left or right wheel reaches the target turning angle; Step S7: it is judged whether the left wheel turning angle deviation signal is greater than the critical turning angle threshold 0.2°: if yes, jump to step S3; if not, jump to step S8; Step S8: the servo proportional valve is set to the middle position, the first reversing ball valve is powered, and the first hydraulic control one-way valve and the second hydraulic control one-way valve are connected to the return oil chamber, so that the cross rod cylinder is locked; Step S9: simultaneously with step S8, the deviations between the left and right wheels and the target turning angles are calculated; Step S10: according to the deviation between the actual turning angle and the target turning angle of the left wheel, the controller sends an instruction signal to control the expansion and contraction of the left and right steering assistance cylinders to reach the target turning angle.

4. The control method of a pump-controlled master tie rod assist valve-controlled electro-hydraulic steering system according to claim 3, characterized in that: The servo motor changes the motor speed through the voltage control signal to adjust the output flow and pressure of the quantitative pump; the electromagnetic reversing valve is controlled by using angular velocity feed-forward-angle feedback control, the left turning is set to positive, the deviation angle between the target turning angle and the actual turning angle of the left steering wheel is used as the feedback signal, the target angular velocity is used as the feed-forward signal, and the sum of the feedback signal and the feed-forward signal is used as the control signal, and the control signal function is as follows: wherein is a control signal, is a target rotation angle, is an actual rotation angle, is a target angular velocity.

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