Adjustable tie rod closed-loop pump-controlled steering system and method based on flow compensation control

Abstract

An adjustable tie rod closed-loop pump-controlled hydraulic steering system based on flow compensation control is provided. The system has an auxiliary flow control test system for compensating for no

Claims

1. An adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control, comprising an adjustable tie rod closed-loop pump-controlled steering system and a flow characteristic test system, the adjustable tie rod closed-loop pump-controlled steering system is the main system, used to achieve multi-mode steering; the flow characteristic test system is an auxiliary test system, used to test and compensate for the nonlinear mapping error of the pump output flow in the main system;the adjustable tie rod closed-loop pump-controlled steering system comprises a closed-loop pump-controlled steering subsystem, a variable tie rod subsystem, and a data acquisition and control subsystem; wherein the closed-loop pump-controlled steering subsystem adjusts the pump output flow by controlling the pump speed, thereby changing the displacements of the left and right steering assist cylinders to achieve precise steering of the steering system; the variable tie rod subsystem changes the inlet flow of the tie rod cylinder by adjusting the opening of the proportional servo valve, thereby changing the displacement of the tie rod cylinder and adjusting the length of the tie rod to adapt to different steering modes; the data acquisition and control subsystem is responsible for collecting the wheel angle signals and the pressures at specified loop positions, according to the collected sensor signals, calculating the control voltages for the servo motor pump speed and the proportional servo-valve opening respectively, and controlling the corresponding hydraulic components to cooperate to complete the steering action; andthe flow characteristic test system measures the change of the pump output flow with the pump source pressure at different pump speeds by changing the speed of the servo-motor pump and the opening of the proportional servo valve, constructs a nonlinear mapping function among the speed, pressure, and flow, and finally compensates for the nonlinear mapping error of the pump output flow.

2. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 1, wherein the closed-loop pump-controlled steering subsystem comprises a servo motor (1), a bidirectional fixed displacement pump (2), an oil tank (3), a first piloted check valve (5), a second piloted check valve (22), a third piloted check valve (9), a fourth piloted check valve (17), a first safety valve (4), a second safety valve (23), a firstelectromagnetic directional valve (6), a left steering assist cylinder (12), and a right steering assist cylinder (14);the variable tie rod subsystem comprises a shuttle valve (20), a proportional servo valve (21), a third safety valve (7), a fifth piloted check valve (8), a sixth piloted check valve (18), a second electromagnetic directional valve (19), and a tie rod cylinder (13); andthe data acquisition and control subsystem comprises a left wheel angle sensor (11), a right wheel angle sensor (15), a first pressure sensor (10), a second pressure sensor (16), a main controller (24), and a servo amplifier (25).

3. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 1, wherein the structure of the flow characteristic test system is as follows:a servo motor (Al), a bidirectional fixed displacement pump (A2), a first safety valve (A4), a second safety valve (A8), a proportional servo valve (A6), an oil tank (A10), a first flow meter (A3), a second flow meter (A9), a first pressure sensor (A5), a second pressure sensor (A7), an auxiliary controller (All), and a servo amplifier (A12).

4. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 2, in the closed-loop pump-controlled steering subsystem:the shaft of the servo motor (1) and the shaft of the bidirectional fixed displacement pump (2) are connected by a coupling to form a servo-motor pump, and the servo motor (1) is electrically connected to the servo amplifier (25); the servo amplifier (25) changes the output torque of the servo motor according to the control voltage, thereby adjusting the speed of the servo-motor pump and finally changing the output flow of the servo motor pump.the rod end chamber of the left steering assist cylinder (12), the rodless end chamber of the right steering assist cylinder (14), and the port B of the third piloted check valve (9) are connected, through the port A of the third piloted check valve (9), they are connected to the left outlet of the servo-motor pump and the port A of the shuttle valve (20), forming the left hand loop of the steering assist cylinder;the rodless end chamber of the left steering assist cylinder (12), the rod-end chamber of the right steering assist cylinder (14), and the port B of the fourth piloted check valve (17) are connected, through the port A of the fourth piloted check valve (17), they are connected to the right outlet of the servo motor pump and the port B of the shuttle valve (20), forming the right hand loop of the steering assist cylinder;the port P of the first safety valve (4) and the port P of the second safety valve (23) are respectively connected to the left and right outlets of the servo-motor pump, and the port T of the first safety valve (4) and the port T of the second safety valve (23) are connected in parallel, and after being connected in parallel, they are connected back to the oil tank (3), forming a protection loop for the servo-motor pump;the port K of the first piloted check valve (5) and the port B of the second piloted check valve (22) are connected in parallel and then connected to the right outlet of the servo motor pump; similarly, the port K of the second piloted check valve (22) and the port B of the first piloted check valve (5) are connected in parallel and then connected to the left outlet of the servo-motor pump; the port A of the first piloted check valve (5) and the port A of the second piloted check valve (22) are connected in parallel and connected back to the oil tank, forming a makeup oil balance loop; andthe port K of the third piloted check valve (9) and the port K of the fourth piloted check valve (17) are connected in parallel and then connected to the port P of the first electromagnetic directional valve (6), the port A of the first electromagnetic directional valve (6) is connected to both the left and right outlets of the servo motor pump, and the port T of the first electromagnetic directional valve (6) is connected back to the oil tank, forming a hydraulic lock for the steering assist cylinder.

5. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 2, in the variable tie rod subsystem:the port A and port B of the shuttle valve (20) are respectively connected to the left and right outlets of the servo-motor pump, the port P of the shuttle valve (20), the port P of the proportional servo valve (21), and the port P of the third safety valve (7) are connected in parallel; the port A of the proportional servo valve (21) is connected to the left chamber of the tie rodcylinder (13) through the port A of the fifth piloted check valve (8), the right chamber of the tie rod cylinder (13) is connected back to the port B of the proportional servo valve (21) through the port B of the sixth piloted check valve (18); the port T of the proportional servo valve (21) and the port T of the third safety valve (7) are both connected back to the oil tank, forming the tie rod cylinder loop;the port K of the fifth piloted check valve (8) and the port K of the sixth piloted check valve (18) are connected in parallel and then connected to the port P of the second electromagnetic directional valve (19), the port A of the second electromagnetic directional valve (19) is connected to the port P of the proportional servo-valve (21), and the port T of the second electromagnetic directional valve (19) is connected back to the oil tank, forming a hydraulic lock for the tie rod cylinder.

6. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 3, in the flow characteristic test system:the servo motor pump composed of the servo motor (Al) and the bidirectional fixed displacement pump (A2) is the power component to be tested in the main system, in the auxiliary test system, the signal of the auxiliary controller (All) is input to the servo amplifier (A12) to control the speed of the servo motor pump, then, the opening of the proportional servo valve (A6) is adjusted to control the pump source pressure, the pump output flow at different speeds and pressures is measured, and a nonlinear mapping among the speed, pressure, and flow is constructed;the left outlet of the servo motor pump is connected in the order of the first flow meter (A3), the first pressure sensor (A5), and the port P of the proportional servo valve (A6), forming the left-hand loop; the right hand loop is connected in the order of the port T of the proportional servo valve (A6), the second pressure sensor (A7), and the second flow meter (A9), and is connected back to the right outlet of the servo motor pump through the second flow meter (A9); the port P of the first safety valve (A4) and the port P of the second safety valve (A8) are respectively connected to the positions of the first pressure sensor (A5) and the second pressure sensor (A7), and finally connected back to the oil tank (A10).

7. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 3, the first safety valve (4), the second safety valve (23), and the third safety valve (7) protect the loop, therefore, the pressure settings of the three safety valves should be higher than the maximum pressure of the protected loop; the firstelectromagnetic directional valve (6), the third piloted check valve (9), and the fourth pilotedcheck valve (17) form a hydraulic lock for the steering assist cylinder, and the secondelectromagnetic directional valve (19), the fifth piloted check valve (8), and the sixth pilotedcheck valve (18) form a hydraulic lock for the tie rod cylinder, the above-mentioned double hydraulic locks cooperate with each other to ensure that the steering system is completely locked; the shuttle valve (20) is used as the connection interface between the steering assist cylinder loop and the tie rod cylinder loop, the main function of the valve is to output the oil from the port with the higher pressure value by comparing the pressure values at both ends of the valve, in other words, to ensure that the inlet (port P) of the proportional servo valve (21) in the tie rod cylinder loop remains unchanged when the outlets of the servo-motor pump are different;the flow characteristic test system explores the nonlinear mapping relationship among the speed, pressure, and flow in the main system by measuring the pump output flow of the servo-motor pump at different speeds and pressures, and constructs the flow nonlinear mapping model of the servo motor pump as follows:Q=f(ne, ps)(l)wherein f (ne, ps) is a nonlinear mapping among the pump speed ne, the pump source pressure ps, and the pump output flow Q established based on the test data of the flow characteristic test system.

8. The adjustable tie rod closed-loop pump-controlled steering system based on flow compensation control according to claim 7, wherein a neural network algorithm is used to construct a flow compensation model to compensate for the influence of the pump speed and the pump source pressure on the pump output flow, this algorithm uses hierarchical calculation, the first layer inputs the pump speed and the pump source pressure to calculate the pump output flow, in other words, the flow nonlinear mapping model, then, according to the pump output flow and the pump source pressure, the pump speed compensation is finally calculated; in addition, theoptimal upper limit value of the pump speed compensation is determined through prior experiments, and a limiting function is used to limit the upper limit value of the speed compensation.

9. An adjustable tie rod closed-loop pump-controlled steering method based on flow compensation control, using the adjustable tie rod closed-loop pump-controlled steering system according to any one of claims 3-7, the control method of the main system comprises the following steps:step SI: start the system: receiving the left and right wheel angle signals through the left and right wheel angle sensors, and obtaining the left and right outlet pressure values of the servo motor pump through the first pressure sensor (10) and the second pressure sensor (16), and inputting them into the main controller (24);step S2: according to the selected steering mode, judging whether locking the tie rod cylinder (13) is necessary, if not, jumping to step S3; if so, jumping to step S8;step S3: judging whether locking the left steering assist cylinder (12) and the right steering assist cylinder (14) are necessary , if not, jumping to step S4; if so, jumping to step S9;step S4: calculating the error values between the expected left and right wheel angle signals and the actual signals respectively, and calculating the pump source pressure value through the left and right outlet pressure values of the servo-motor pump;step S5: calculating the expected voltage signal of the servo amplifier (25) through the main controller (24) according to the expected and actual left and right wheel angle signals, and calculating the control voltage signal for the opening of the proportional servo valve (21);step S6: according to the expected voltage signal of the servo amplifier (25) in step S5 and the left and right outlet pressure values of the servo motor pump obtained in step SI, calculating the pump speed compensation voltage of the servo amplifier (25) through a neural network algorithm, limiting size with a limiting function, and finally adding the two to obtain the input voltage signal of the servo amplifier (25);step S7: the servo motor pump outputs the motor torque according to the input voltage signal of the servo amplifier (25) to change the pump speed, thereby controlling the displacements of the left steering assist cylinders (12) and the right steering assist cylinder (14) and making the leftand right wheel angles reach the specified positions;step S8: the second electromagnetic directional valve (19) is energized, the pilot oil circuits of the fifth piloted check valve (8) and the sixth piloted check valve (18) are connected to the oil return chamber, at this time, the piloted check valves act as one-way valves, and the tie rod cylinder is locked; andstep S9: stop the servo motor pump; the first electromagnetic directional valve (6) is energized, the pilot oil circuits of the third piloted check valve (9) and the fourth piloted check valve (17) are connected to the oil return chamber, at this time, the piloted check valves act as one-way valves, and the left steering assist cylinders (12) and the right steering assist cylinders (14) are locked.

10. The adjustable tie rod closed-loop pump-controlled steering method according to claim 9, wherein the output flow of the servo motor pump needs to match the flow requirements of the steering assist cylinder loop and the tie rod cylinder loop; the calculation is as follows:da>0da<0(2)wherein vl is the speed of the left steering assist cylinder, vr is the speed of the right steering assist cylinder, vH is the speed of the tie rod cylinder, Ais the area of the rodless end chamber of the steering assist cylinder, a is the area of the rod-end chamber of the steering assist cylinder, and Ah is the area of the tie rod cylinder chamber;vl, vr, and vh may all be expressed as function expressions with the left and right wheel angles as independent variables, therefor, the output flow is closely related to the left and right wheel angle signals, the servo motor pump may be jointly controlled by the left and right wheel angle error signals, by adjusting the control gains of the two error signals, the control accuracy of the system may be improved, and the optimal control gains of the left and right wheel angle error signals may be searched through the particle swarm optimization algorithm; in addition, based on the expected and actual left and right wheel angle signals, the corresponding tie rod length is calculated, then, the error value between the expected displacement and the actual displacement of the tie rod cylinder (13) is further calculated, the opening of the proportional servo valve (21)is adjusted according to this cylinder.error value, thereby controlling the displacement of the tie rod

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