CN104443025B - Electro-hydraulic servo pure rolling steering system for multi-axis vehicle and control method - Google Patents

Abstract

The invention discloses an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle. The steering system includes a telescopic rod cylinder, a left steering cylinder, a right steering cylinder, a hydraulic control check valve, a first servo proportional valve, The second servo proportional valve and the controller electrically connected between the two valves. The electro-hydraulic servo composite control is performed on the three actuators through two servo proportional valves to arbitrarily adjust the rotation angle of the steering wheels on both sides, effectively ensuring that each steering wheel meets the Ackerman steering conditions required for pure rolling, thereby achieving high Responsive and highly precise dynamic steering. The preferred steering system also includes an externally controlled hydraulically controlled one-way valve, which can electro-hydraulicly lock the telescopic cylinder of the transverse tie rod to ensure the pure rolling steering effect of the system while reducing the risk of its high-speed driving, thus improving the multi-axis The safety of the vehicle at high speed. The invention also discloses a steering control method for pure rolling of a multi-axle vehicle and a multi-axle vehicle with the steering system.

Description

An electro-hydraulic servo steering system and control method for pure rolling of multi-axle vehicles

technical field

The invention relates to an electro-hydraulic servo steering system and a steering control method for pure rolling of a multi-axle vehicle, which are applied in the field of automobile steering. The invention also relates to a multi-axle vehicle with the electro-hydraulic servo steering system.

Background technique

Large-scale wheeled vehicles are widely used in infrastructure construction (such as large-tonnage all-terrain cranes, large-scale beam transport vehicles and mining dump trucks and other civilian equipment) and military heavy industry (such as large missile transport vehicles, heavy electronic launch vehicles and traction vehicles. and other military special vehicles). High-performance multi-axis steering can significantly improve the low-speed maneuverability and high-speed handling stability of large wheeled vehicles, and help promote the development of related technologies such as car-like robots and multi-wheeled lunar vehicles. It has become a measure of modern large-scale heavy vehicles. It is one of the key technologies for the development level of vehicles and cutting-edge transportation equipment, and its core technology breakthrough is of great significance.

However, for large multi-axle vehicles, the steering load is large, and a certain geometric relationship needs to be guaranteed between the rotation angles of the wheels. Although the traditional mechanical rocker-arm hydraulic power steering system helps to ensure the rotation angle relationship between the wheels, it cannot There are obvious defects such as single steering mode and poor flexibility. This type of system has gradually developed towards an electro-hydraulic control steering system with strong flexibility, high dynamic steering precision, and large driving torque.

At present, the design of the electro-hydraulic control steering system mainly revolves around the steering trapezoidal mechanism and the electro-hydraulic control circuit: (1) In terms of the steering trapezoidal mechanism: the trapezoidal mechanism is optimized through virtual prototyping technology or optimization algorithm, so that the optimized trapezoidal mechanism Approximate the Ackermann mechanism to improve the steering accuracy (for example, refer to patents 201110097127.6 and 93104300.x); or add a fixed groove roller pair or a cam rotation pair to the trapezoidal mechanism to make the length of the transverse tie rod variable and realize the pure rolling of the wheel Steering, to reduce tire wear (as referenced patent 201110154053.5 and 01252825.3). (2) Electro-hydraulic control circuit: adopt the direct transverse tie rod to drive the steering method, such as replacing the transverse tie rod with a double-rod hydraulic cylinder as the actuator, and combine the electro-hydraulic control valve and the control method to suppress the road disturbance load to enhance the stability of the steering system (for example, refer to the patent EP1852329A2); or use the electro-hydraulic proportional system to realize the steering, such as realizing the precise control of the reversing and the flow through the electronically controlled reversing valve and the proportional throttle valve, so as to realize the proportional steering through the matching action of each component. Fast response and sensitive steering operation (for example, refer to patent 201210370470.8); or use an electro-hydraulic servo system to realize steering, such as using a servo proportional valve to control a double steering cylinder to drive a trapezoidal steering, which not only has a large driving load but also has a high frequency response and no zero Bit dead zone (for example, refer to patent 201010265429.5).

The existing patents help to improve the steering flexibility and dynamic steering accuracy of multi-axle vehicles, but there are still some shortcomings as follows:

1) The high-quality design of the pure rolling steering trapezoidal mechanism has encountered a bottleneck. All-wheel pure rolling steering of multi-axle vehicles can significantly reduce tire wear and improve driving stability. However, because the traditionally designed steering trapezoidal mechanism is a four-bar mechanism, the Ackermann angle relationship of pure rolling cannot be strictly satisfied by optimizing the steering trapezoidal mechanism, so pure rolling in the true sense cannot be realized. In addition, through the pure rolling steering mechanism for the deformation of the steering mechanism (such as reference patents 201210423486.0, 201010605346.6, etc.), the pure rolling condition in mechanics is met, but it brings problems such as large turning radius and difficult layout. Therefore, there is still a need for further improvement in the mechanism design for realizing the pure rolling steering trapezoid.

2) Precise dynamic steering with high response under pure rolling conditions cannot be effectively realized. The steering system of a multi-axle vehicle requires a high-response and high-precision steering trapezoid, and it also requires each steering wheel to meet the Ackermann steering conditions as much as possible. The current steering system design mainly revolves around the above aspects (for example, patent 201010255429.5 improves steering response speed and precision through electro-hydraulic servo control; patents 201110154053.5 and 01252825.3 use new structural design to achieve pure rolling). However, since most structural designs with pure rolling function cannot effectively achieve high-response precise control at the same time, how to achieve the integration of structural innovation and effective control, and break through the high-response precise dynamic steering system design under pure rolling conditions, there are still obvious problems. insufficient.

3) The safety of dynamic steering in pure rolling state needs to be strengthened. As far as the current conventional steering trapezoid is concerned, the vehicle often turns within a small corner range when driving at high speed. If the steering mechanism fails at this time, it is easy to cause great harm (such as tire skidding, steering loss of control, etc.), so its safety is particularly important. However, the existing steering mechanism with pure rolling function has defects in the steering safety of the vehicle at high speed, and needs to be further improved.

Contents of the invention

The purpose of the present invention is to provide an electro-hydraulic servo steering system for pure rolling of multi-axle vehicles, which performs electro-hydraulic servo composite control on multiple actuators through dual servo proportional valves, so as to ensure that each steering wheel meets the Ak required to realize pure rolling. Mann steering conditions, and realize high-response and high-precision dynamic steering; preferably, the steering system can electro-hydraulic lock the telescopic cylinder of the transverse tie rod to ensure the pure rolling steering effect of the steering system while reducing the risk of its high-speed driving and improving multiple The safety of axle vehicles at high speeds. Another object of the present invention is to provide a steering control method for pure rolling of a multi-axle vehicle. It is also an object of the invention to provide a multi-axle vehicle with said steering system.

One of the technical solutions adopted in the present invention to achieve the above object is as follows:

An electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle, the multi-axle vehicle includes a first axle and rear steering axles, the electro-hydraulic servo steering system for each rear steering axle includes a fuel tank 1, a hydraulic pump 2. The first servo proportional valve 4, the vehicle frame 16, the left steering cylinder 9, and the right steering cylinder 14; the rod chamber of the left steering cylinder 9 and the rodless chamber of the right steering cylinder 14 form the first working oil circuit R1, the rodless chamber of the left steering power cylinder 9 and the rod chamber of the right steering power cylinder 14 form the second working oil circuit R2, and the first working oil circuit R1 and the second working oil circuit R2 are connected with the first working oil circuit respectively. The A and B working oil ports of the servo proportional valve 4 are connected;

The electro-hydraulic servo steering system includes a telescopic rod cylinder 12, a second servo proportional valve 22, and an electronic control system;

The piston part of the telescopic rod cylinder 12 is hinged to the first trapezoidal arm 10 on one side, and the cylinder part of the telescopic rod cylinder 12 is hinged to the second trapezoidal arm 13 on the other side;

The two working chambers of the transverse rod telescopic cylinder 12 are respectively connected with the A and B working oil ports of the second servo proportional valve 22 to respectively form the third working oil circuit R3 and the fourth working oil circuit R4; the first servo proportional valve 4 and the P port of the second servo proportional valve 22 are respectively connected with the oil inlet circuit, and the T ports of the first servo proportional valve 4 and the second servo proportional valve 22 are connected with the oil tank 1;

The electronic control system is used to calculate the target length of the telescopic cylinder of the transverse tie rod according to the target rotation angle of the left and right wheels of the controlled steering axle, and output it to the second servo proportional valve in the electro-hydraulic servo steering system where the controlled steering axle is located. The command signal corresponding to the target length of the telescopic rod telescopic cylinder is output to the first servo proportional valve in the electro-hydraulic servo steering system where the controlled steering axle is located, which is the same as the target rotation angle of the right or left wheel. The corresponding command signals are adjusted in real time according to the displacement feedback signal of the telescopic rod telescopic cylinder of the controlled steering axle and the feedback rotation angle signal of the right or left wheel.

The telescopic rod cylinder 12 is a double-rod cylinder, and the effective working areas of the rod cavities on both sides of the telescopic cylinder are equal.

The system includes a first hydraulically controlled check valve 5, a second hydraulically controlled check valve 6, a third hydraulically controlled check valve 19 and a fourth hydraulically controlled check valve 20, which are respectively connected in series to the first working oil circuit. R1, the second working oil circuit R2, the third working oil circuit R3, the fourth working oil circuit R4 four oil circuits;

The pilot oil of the first hydraulic control check valve 5 and the second hydraulic control check valve 6 is controlled by the first electromagnetic reversing valve 3; the third hydraulic control check valve 19 and the fourth hydraulic control check valve The pilot oil of the one-way valve 20 is controlled by the first electromagnetic reversing valve 23; the first electromagnetic reversing valve 3 and the second electromagnetic reversing valve 23 are two-position three-way valves.

The system includes a first charge relief valve group 7, a second charge relief valve group 8, a third charge relief valve group 17 and a fourth charge relief valve group 18, which are respectively connected in series with the first There are four oil circuits including working oil circuit R1, second working oil circuit R2, third working oil circuit R3 and fourth working oil circuit R4.

The first charge oil relief valve group 7, the second charge oil relief valve group 8, the third charge oil relief valve group 17 and the fourth charge oil relief valve group 18 have the same structure, each of which includes a relief Valve 24 and a one-way valve 25, and one-way valve 25 is connected in parallel with overflow valve 24, and one-way valve 25 is used for making the inlet and outlet of overflow valve 24 be in positive cut-off and reverse conduction state.

The electronic control system includes: a controller 21, a rotation angle sensor 15 for detecting the right or left wheel rotation angle of the steering axle, a displacement sensor 11 for detecting the length of the telescopic cylinder of the transverse tie rod, a first electromagnetic reversing valve 3 and The second electromagnetic reversing valve 23;

The controller 21 is electrically connected to the first servo proportional valve 4, the second servo proportional valve 22, the rotation angle sensor 15 and the displacement sensor 11, the first electromagnetic reversing valve 3 and the second electromagnetic reversing valve 23;

Wherein the controller 21, the first servo proportional valve 4, the transverse tie rod telescopic cylinder 12 and the displacement sensor 11 form a closed-loop control of the length of the transverse tie rod telescopic cylinder; at the same time, the controller 21, the second servo proportional valve 22, the right steering cylinder 14, the left The power steering cylinder 9 and the right or left steering angle sensor 15 form a closed-loop control of the steering angle of the right or left wheel.

The present invention also includes another technical feature:

A steering control method for an electro-hydraulic servo steering system oriented to pure rolling of a multi-axle vehicle, comprising the following steps:

Step 1: The electro-hydraulic servo steering system inputs the target angle signals of the left and right wheels of the controlled steering axle to the controller of the steering axle;

Step 2: Determine whether it is necessary to lock the telescopic rod telescopic cylinder within the critical locking angle range on the left and right sides of the center of the steering wheel: if not, skip to step 3; if necessary, skip to step 9;

Step 3: The controller calculates the target length of the telescopic cylinder of the transverse tie rod according to the target rotation angle signals of the left and right wheels, and uses the target length and the target rotation angle of the right or left wheel as two control targets to control the system;

Step 4: Detect the actual length of the telescopic cylinder of the transverse tie rod of the controlled steering axle and the actual rotation angle of the right or left wheel;

Step 5: Calculate the deviation between the actual length of the telescopic cylinder of the transverse rod and the target length, and calculate the deviation between the actual rotation angle of the right or left wheel and the target rotation angle;

Step 6: According to the length deviation signal of the transverse rod telescopic cylinder, the controller sends the first command signal to the second servo proportional valve to control the operation of the second servo proportional valve; at the same time, according to the right or left wheel angle deviation signal, the first servo The proportional valve sends the second command signal to control the first servo proportional valve to work;

Step 7: The second servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the telescopic rod cylinder, so that the actual length of the telescopic cylinder is close to the target length. The first servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the left and right steering cylinders, so that the right Or the actual turning angle of the left wheel is close to the target turning angle;

Step 8: The controller adjusts the two command signals in real time according to the actual length of the telescopic rod telescopic cylinder fed back by the displacement sensor and the rotation angle sensor and the actual rotation angle of the right or left wheel. Under the joint control of the two command signals, the steering The trapezoidal mechanism realizes pure rolling steering, making the left and right wheels reach the target turning angle;

Step 9: Determine whether the right or left wheel rotation angle is greater than the critical locking angle: if it is greater, go to step 3; if not, go to step 10;

Step 10: Set the second servo proportional valve in the neutral position, the second electromagnetic directional valve is energized, and the pilot oil of the third hydraulic control check valve and the fourth hydraulic control check valve are returned to the oil, so that the horizontal tie rod telescopic cylinder locking.

Step 11: Synchronously with step 10, detect the actual rotation angle of the right or left wheel of the controlled steering axle;

Step 12: Calculate the deviation between the actual rotation angle of the right or left wheel and the target rotation angle;

Step 13: According to the right or left wheel angle deviation signal, the controller sends a command signal to the first servo proportional valve to control the first servo proportional valve to work;

Step 14: The first servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the left and right steering cylinders, so that the actual rotation angle of the right or left wheel is close to the target rotation angle;

Step 15: The controller adjusts the instruction signal in real time according to the actual rotation angle of the right or left wheel fed back by the rotation angle sensor. Under the control of the instruction signal, the steering trapezoidal mechanism realizes the steering, so that the right or left wheel reaches the target rotation angle .

The critical locking rotation angle is plus or minus 5°-15°.

The controller 21 is a programmable logic controller or a single chip microcomputer, and the response frequency of the controller is adapted to the response frequency of the first servo proportional valve 4 and the second servo proportional valve 22 .

The beneficial effects that the present invention possesses are:

1) The steering trapezoidal mechanism is designed based on the variable-length transverse tie rod controlled by electro-hydraulic servo, which breaks through the design bottleneck of high-quality pure rolling steering mechanism. By replacing the tie rods in the traditional steering trapezoid with the telescopic rod cylinder, and using the electro-hydraulic servo system to precisely control it, the original four-bar mechanism of the steering trapezoid is transformed into a five-bar mechanism with a built-in telescopic rod cylinder. The mechanism has two degrees of freedom, and can control the steering angle of both sides of the wheels at the same time, realizing the Ackermann steering of the two sides of the wheels; at the same time, it has the advantages of convenient layout, labor-saving operation and small turning radius. The precision of the Ackerman turn creates the conditions.

2) Through the electro-hydraulic servo composite control of the double-sided trapezoidal arm and the transverse tie rod, high-response and high-precision dynamic steering under pure rolling conditions is realized. The double-sided trapezoidal arm is controlled by the servo proportional valve to provide the steering drive torque to realize the high-response and high-precision steering control of the trapezoidal mechanism; at the same time, the servo proportional valve is used to control the telescopic cylinder of the transverse tie rod to realize the dynamic variable length control of the telescopic cylinder with high response. Therefore, the electro-hydraulic servo composite control is performed on the three actuators (with two degrees of freedom) through the dual servo proportional valve, and the rotation angle of the steering wheels on both sides can be adjusted arbitrarily, so that the rotation angle of the two-side wheels can fully meet the steering requirements of multi-axle vehicles. Ackermann conditions, and guarantee high response and high precision in pure roll steering process.

3) The telescopic cylinder of the transverse tie rod is locked by electro-hydraulic control, which effectively improves the safety of the multi-axle vehicle at high speed. When the vehicle is running at high speed, the steering angle often works in a small corner range, and the lateral tie rod is locked by electro-hydraulic control to re-convert it from a metamorphic steering trapezoid to a conventional steering trapezoid. As a result, the danger caused by the failure of the metamorphic part of the mechanism can be effectively avoided, and the pure rolling steering effect of the metamorphic mechanism can be guaranteed (at small turning angles, the fixed-length transverse tie rod can also approximate the Ackermann steering) while reducing its high speed. Risks during driving, improving the safety of multi-axle vehicles at high speeds.

Description of drawings

Figure 1 is a schematic diagram of an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle.

Figure 2 is a schematic diagram representing the relationship between the length of the transverse tie rod and the rotation angle of the wheels on both sides,

Fig. 3 is a block diagram of the control principle of an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle.

Fig. 4 is a flow chart of the control method of the electro-hydraulic servo steering system of the present invention,

Fig. 5 is a schematic diagram of the electro-hydraulic servo steering system applied to the pure rolling of multi-axle vehicles according to the present invention.

In the figure: 1. Fuel tank, 2. Hydraulic pump, 3. The first electromagnetic reversing valve, 4. The first servo proportional valve, 5. The first hydraulic control check valve, 6. The second hydraulic control check valve, 7 , The first oil-charging overflow valve group, 8, the second oil-charging overflow valve group, 9, the left steering cylinder, 10, the first trapezoidal arm, 11, the displacement sensor, 12, the transverse rod telescopic cylinder, 13, the second Two trapezoidal arms, 14. Right steering power cylinder, 15. Angle sensor, 16. Frame, 17. The third charge relief valve group, 18 The fourth charge relief valve group, 19. The third hydraulic control one-way Valve, 20, fourth hydraulic control check valve, 21, controller, 22, second servo proportional valve, 23, second electromagnetic reversing valve, 24, overflow valve, 25, check valve, R1, first Working oil circuit, R2, the second working oil circuit, R3, the third working oil circuit, R4, the fourth working oil circuit.

detailed description

The specific implementation of the present invention will be described below in conjunction with the drawings and examples.

Figure 1 is a schematic diagram of an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle.

An electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle, the multi-axle vehicle includes a first axle and rear steering axles, the electro-hydraulic servo steering system for each rear steering axle includes a fuel tank 1, a hydraulic pump 2. The first servo proportional valve 4, the frame 16, the left steering cylinder 9, the right steering cylinder 14; the piston rod of the left steering cylinder 9 is hinged to the first trapezoidal arm 10, and the cylinder body is hinged to the frame 16, And the piston rod of the right power steering cylinder 14 is hinged with the second trapezoidal arm 13, and its cylinder body is also hinged with the vehicle frame 16; the rod chamber of the left power steering cylinder 9 and the rodless chamber of the right power steering cylinder 14 form the first working Oil circuit R1, the rodless chamber of the left steering power cylinder 9 and the rod chamber of the right steering power cylinder 14 form the second working oil circuit R2, and the two working oil circuits of R1 and R2 are connected with A and B of the first servo proportional valve 4 respectively. The working oil port is connected.

The electro-hydraulic servo steering system also includes a telescopic rod cylinder 12, a second servo proportional valve 22 and an electronic control system.

The piston part of the telescopic rod cylinder 12 is hinged to the first trapezoidal arm 10 on one side, and the cylinder part of the telescopic rod cylinder 12 is hinged to the second trapezoidal arm 13 on the other side.

The two working chambers of the transverse rod telescopic cylinder 12 are respectively connected with the A and B working oil ports of the second servo proportional valve 22 to respectively form the third working oil circuit R3 and the fourth working oil circuit R4; the first servo proportional valve 4 The P port of the second servo proportional valve 22 is connected with the oil inlet circuit, and the T ports of the first servo proportional valve 4 and the second servo proportional valve 22 are connected with the oil tank 1 .

Preferably, the telescopic rod cylinder 12 is a double-rod cylinder, and the effective working areas of the rod cavities on both sides of the telescopic rod cylinder are equal.

Preferably, an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle includes a first hydraulic control check valve 5, a second hydraulic control check valve 6, a third hydraulic control check valve 19 and a fourth hydraulic control check valve. The one-way valve 20 is connected in series with four oil circuits of R1, R2, R3 and R4 respectively. The pilot oil of the first hydraulic control check valve 5 and the second hydraulic control check valve 6 is controlled by the first electromagnetic reversing valve 3; the third hydraulic control check valve 19 and the fourth hydraulic control check valve The pilot oil of the one-way valve 20 is controlled by the second electromagnetic reversing valve 23; the first electromagnetic reversing valve 3 and the second electromagnetic reversing valve 23 are two-position three-way valves.

Preferably, an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle includes a first charge relief valve group 7, a second charge relief valve group 8, a third charge relief valve group 17, a fourth Oil supplement overflow valve group 18 is respectively connected in series with four oil circuits of R1, R2, R3 and R4. The first charge oil relief valve group 7, the second charge oil relief valve group 8, the third charge oil relief valve group 17, and the fourth charge oil relief valve group 18 have the same structure, each including a relief valve 24 and a one-way valve 25, and the one-way valve 25 is connected in parallel with the overflow valve 24, and the one-way valve 25 is used to make the inlet and the outlet of the overflow valve 24 be in a positive cut-off and reverse conduction state.

The electronic control system includes: a controller 21, a rotation angle sensor 15 for detecting the right (or left) side wheel rotation angle of the steering axle, a displacement sensor 11 for detecting the length of the telescopic cylinder of the transverse tie rod, and a first electromagnetic reversing valve , the second electromagnetic reversing valve; the controller 21 is electrically connected to the first servo proportional valve 4, the second servo proportional valve 22, the angle sensor 15, the displacement sensor 11, the first electromagnetic reversing valve and the second electromagnetic reversing valve .

Fig. 2 is a schematic diagram showing the relationship between the length of the transverse tie rod and the rotation angle of the wheels on both sides.

When the multi-axle vehicle is turning, all the wheels are in a pure rolling steering state, which satisfies the Ackermann steering theorem, and the wear of the tires will be significantly reduced, thereby improving the stability and safety of the vehicle. A multi-axle vehicle includes multiple steering bridges (generally, the number of steering bridges is n≥3). During the steering process, if the pure rolling of each steering wheel is to be ensured, the required rotation angle of each wheel can be calculated according to Ackermann's theorem. Take the steering bridge of the nth bridge as an example, as shown in the figure, assume that the rotation angles of the left and right side wheels are α _n and β _n under pure rolling conditions calculated by Ackerman’s theorem, and the lengths of the trapezoidal arms of the left and right side wheels are m, when the tire is in the neutral position, the angle between the trapezoidal arm and the axle of the steering axle is γ, and the distance between the kingpins of the steering wheels on both sides is K.

Traditional multi-axis vehicle steering systems are driven by a steering trapezoidal mechanism, but the steering axle driven by the steering trapezoidal mechanism has only one degree of freedom in steering, which can only ensure that the steering angle of one of the steering wheels on both sides is completely consistent with the target; while the other The side wheel rotation angle can only be fitted by the steering trapezoidal mechanism, so that the wheel rotation angles on both sides meet the Ackermann condition as much as possible, that is, the traditional steering trapezoidal mechanism cannot strictly realize pure rolling steering on the left and right sides.

Considering that the lateral tie rods can be freely extended and retracted, when the left and right side wheels realize pure rolling steering, according to the Ackermann theorem in the corresponding steering mode, the calculated value of the left and right side wheel rotation angle of the nth bridge that satisfies the Ackermann rotation angle relationship is α _n and β _n . According to the geometric dimensions and geometric relationship of the mechanism, the length of the CD segment at the position of the steering tie rod in the figure can be calculated, namely:

It can be seen that the length of the CD segment is related to the rotation angles α and β of the wheels on both sides. Obviously, the length of the CD segment changes with the steering angle. To satisfy the Ackermann condition for both wheels at the same time, the length of the transverse tie rod needs to be changed in real time, that is, to be elongated or shortened to meet the Ackermann condition. In addition, except for the three variables of α _n , β _n and L _cd , the rest of the above formula are all constants, through which two variables can be combined with the above formula to obtain another variable, that is, α _n =f(β _n ,L _cd ) . Therefore, the left wheel rotation angle α _n can be controlled by controlling the right wheel rotation angle β _n and the length L _cd of the transverse tie rod, so that the wheel rotation angles on both sides satisfy the Ackermann condition and realize pure rolling. Of course, the right wheel rotation angle β _n can also be controlled by controlling the left wheel rotation angle α _n and the length L _cd of the transverse tie rod, and the principle is the same.

Fig. 3 is a control principle block diagram of an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle.

With reference to Figures 1 to 3, the electronic control system is used to calculate the target length of the telescopic rod telescopic cylinder according to the target angles of the left and right wheels of the controlled steering axle, and provide The second servo proportional valve 22 in the steering system outputs a command signal corresponding to the target length of the transverse tie rod telescopic cylinder; at the same time, the first servo proportional valve 22 in the electro-hydraulic servo steering system where the controlled steering axle is located Valve 4, which outputs a command signal corresponding to the target rotation angle of the right (or left) side wheel, and feeds back the rotation angle signal of the right (or left) side wheel according to the displacement feedback signal of the telescopic rod telescopic cylinder of the controlled steering axle , to adjust each instruction signal in real time.

According to the steering angle of the first axle (the steering wheel controls the steering machine to steer, usually a mechanical hydraulic control method) and the selected steering mode of the multi-axle vehicle, the following steering axles that meet the requirements of pure rolling steering can be calculated according to Ackerman's theorem. The steering angles of the left and right wheels of the bridge, assuming that the nth bridge is the controlled steering bridge, the target turning angles of the left and right wheels of the nth bridge are α _n and β _n .

With reference to Figures 1 to 3, the working principle of the electro-hydraulic servo steering system for pure rolling of multi-axle vehicles is as follows:

First, the left and right wheel rotation angles α _n and β _n of the nth bridge are input to the controller as the target rotation angle, and the controller calculates the required length L _cd of the telescopic cylinder of the transverse tie rod according to the formula (1), and uses this length L _cd and the right wheel rotation angle β _n (here, the right steering wheel is taken as an example, and the principle of changing it to the left steering wheel is similar) as the target length and the target rotation angle for control respectively.

Secondly, the displacement sensor 11 installed on the horizontal pulling cylinder telescopic cylinder 12 detects the actual displacement of the horizontal pulling cylinder telescopic cylinder 12, according to the structural size of the horizontal pulling cylinder telescopic cylinder 12, its actual length L _cd ' can be calculated, and the controller passes Comparing and calculating the actual length with the target length, the length deviation signal ΔL _cd =L _cd -L _cd ' can be obtained; at the same time, the rotation angle sensor 15 installed at the kingpin of the right steering wheel detects the actual rotation angle β _n ' of the right wheel, and the control The controller compares and calculates the actual rotation angle with the target rotation angle to obtain the rotation angle deviation signal Δβ _n =β _n -β _n '.

Thirdly, the controller converts the deviation signals ΔL _cd and Δβ _n into the first command signal μ through corresponding control algorithms such as proportional control, PID control or other control methods according to the length deviation signal ΔL _cd and the rotation angle deviation signal Δβ _{n 1} and the second command signal μ ₂ ; the two command signals μ ₁ and μ ₂ respectively control the action of the first servo proportional valve 4 and the second servo proportional valve 22, so that the spool produces a corresponding displacement.

Then, the second servo proportional valve 22 is a three-position four-way valve. When it is in the cross position, the F chamber of the transverse tie rod telescopic cylinder 12 enters high-pressure oil, and the E chamber returns oil. At this time, the transverse tie rod telescopic cylinder 12 is in an extended state. . When it was in the parallel position, the E cavity of the transverse tie rod telescopic cylinder 12 entered high-pressure oil, and the F cavity returned the oil, and now the transverse tie rod telescopic cylinder 12 was in a shortened state. When it is in the "O" type neutral position, the E cavity and the F cavity of the transverse tie rod telescopic cylinder 12 are closed, and now the transverse tie rod telescopic cylinder 12 is not telescopic. The length deviation signal ΔL _cd causes the spool action of the second servo proportional valve 4 to generate a corresponding opening amount, which causes the telescopic rod telescopic cylinder 12 to expand and contract, and makes it show a trend that the actual length L _cd ' is close to the target length L _cd , thereby reducing The small length deviation signal makes it a negative feedback closed-loop control.

Simultaneously, the first servo proportional valve 4 is a three-position four-way valve. When it is in the cross position, the rod chamber of the right steering cylinder 14 and the rodless chamber of the left steering cylinder 9 are all connected with high-pressure oil, and the right steering cylinder The rodless chamber of 14 and the rod chamber of left power steering cylinder 9 all lead back to oil; this moment, right power steering cylinder 14 was in shortened state, and left power steering cylinder 9 was in elongated state, turning to trapezoidal counterclockwise rotation. When the first servo proportional valve 4 is in the parallel position, the rodless chamber of the right power steering cylinder 14 and the rod chamber of the left power steering cylinder 9 are connected with high-pressure oil, and the rod chamber of the right power steering cylinder 14 and the rod chamber of the left power steering cylinder The rodless cavity of 9 all leads back to oil, and now the right power steering cylinder 14 is in an extended state, and the left power steering cylinder 9 is in a shortened state, and the trapezoidal mechanism turns clockwise. When the first servo proportional valve 4 is in the "O" type neutral position, the rod cavity and the rodless cavity of the left steering cylinder 9 and the right steering cylinder 14 are all closed, and now the left steering cylinder 9 and the right steering cylinder 14 are not flexible. The rotation angle deviation signal Δβ _n causes the spool action of the first servo proportional valve 4 to generate a corresponding opening amount, which causes the right steering cylinder 14 and the left steering cylinder 9 to expand and contract, and makes the right wheel present the actual rotation angle β _n ' close to the target The trend of the rotation angle β _n , and then reduce the deviation signal of the rotation angle, making it a negative feedback closed-loop control.

Finally, the two-degree-of-freedom control of the steering trapezoidal mechanism is realized through two servo proportional valves to control the telescopic cylinder of the transverse tie rod and the left and right steering cylinders respectively, and then realize the precise closed-loop control of the left and right wheel angles, effectively ensuring The steering angle of both sides fully satisfies the Ackermann condition required for multi-axle vehicle steering, realizing pure rolling steering. Since the actuators are all electro-hydraulic servo controls, they have high response and high precision, which ensures the high response and high precision of pure rolling dynamic steering.

When it is necessary to close the two cavities of the telescopic rod 12 of the lateral tie rod to keep it in a non-telescopic state, if only the second servo proportional valve 22 is in the neutral position, the precise locking of the telescopic rod 12 of the lateral rod cannot be guaranteed due to leakage of the slide valve. If the second servo proportional valve 22 is on the neutral basis, and the pilot oil of the third hydraulic control check valve 19 and the fourth hydraulic control check valve 20 is passed back to the oil through the second electromagnetic reversing valve 23, that is The transverse tie rod telescopic cylinder 12 can be precisely locked through the two-way hydraulically controlled one-way valve to ensure that the transverse tie rod telescopic cylinder 12 does not expand or contract.

In the same way, when it is necessary to close the working chambers of the left and right steering cylinders to keep them in a non-expandable state, if only the first servo proportional valve 4 is in the neutral position, due to the leakage of the slide valve, it is impossible to ensure that the left and right steering cylinders precise locking. If the first servo proportional valve 4 is in the middle position, and the pilot oil of the first hydraulic control check valve 5 and the second hydraulic control check valve 6 is passed back to the oil through the first electromagnetic reversing valve 3, that is The left and right steering booster cylinders can be precisely locked through the two-way hydraulic control check valve to ensure that the left and right steering booster cylinders do not expand or contract.

The first electromagnetic reversing valve 3 and the second electromagnetic reversing valve 23 involved in the present invention are both two-position three-way valves. Through the reversing function of the two-position three-way valve, the control oil of each hydraulic control check valve can be Switch between high pressure oil and oil return. If the first electromagnetic reversing valve 3 and the second electromagnetic reversing valve 23 are replaced with two-position two-way valves, since the pilot oil circuit only has two states of connecting high-pressure oil and disconnecting high-pressure oil, the hydraulic control one-way The pilot control cavity of the valve forms a dead volume cavity, which cannot effectively ensure the pressure relief of the hydraulic control check valve, which leads to the failure of the hydraulic control check valve to work normally. Therefore, the first electromagnetic reversing valve 3 and the second electromagnetic reversing valve 23 must select two-position three-way valves.

When the telescopic cylinders of the transverse tie rods and the left and right steering cylinders are locked and closed, and the steering wheel of the multi-axle vehicle is impacted by a strong external load, instantaneous high pressure will be generated in the telescopic cylinders of the transverse tie rods and the left and right steering cylinders. The set pressure of the relief valve in the relief valve group can effectively protect each hydraulic cylinder from being damaged by instantaneous high pressure. It should be noted that when the closed cavity overflows through the relief valve, it is easy to generate negative pressure. At this time, oil can be replenished through the check valve connected in parallel with the relief valve to eliminate the generation of negative pressure.

The above description takes the right wheel steering angle as the control target. If it is changed to take the left wheel rotation angle as the control target, the principle is similar, that is, the right wheel rotation angle can be controlled by controlling the lateral tie rod telescopic cylinder and the left wheel rotation angle, and finally the precise control of the left and right wheel steering can be realized. Since the control methods involved are similar, they will not be described in detail.

Fig. 4 is a flow chart of the control method of the electro-hydraulic servo steering system of the present invention.

Include the following steps:

Step 1: The electro-hydraulic servo steering system inputs the target angle signals of the left and right wheels of the controlled steering axle to the controller of the steering axle;

Step 2: Determine whether it is necessary to lock the telescopic rod telescopic cylinder within the critical locking angle range on the left and right sides of the center of the steering wheel: if not, skip to step 3; if necessary, skip to step 9;

Step 3: The controller calculates the target length of the telescopic cylinder of the transverse tie rod according to the target rotation angle signals of the left and right wheels, and controls the system with the target length and the target rotation angle of the right (or left) side wheel as two control targets;

Step 4: Detect the actual length of the telescopic cylinder of the transverse tie rod of the controlled steering axle and the actual angle of rotation of the right (or left) side wheel;

Step 5: Calculate the deviation between the actual length of the telescopic rod cylinder and the target length, and at the same time calculate the deviation between the actual rotation angle of the right (or left) side wheel and the target rotation angle;

Step 6: According to the length deviation signal of the telescopic cylinder of the transverse tie rod, the controller sends the first command signal to the second servo proportional valve to control the operation of the second servo proportional valve; at the same time, according to the right (or left) side wheel angle deviation signal to the second A servo proportional valve sends a second command signal to control the operation of the first servo proportional valve;

Step 7: The second servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the telescopic rod cylinder, so that the actual length of the telescopic cylinder is close to the target length. The first servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the left and right steering cylinders, so that the right The actual turning angle of the (or left) side wheel is close to the target turning angle;

Step 8: The controller adjusts the two command signals in real time according to the actual length of the telescopic rod telescopic cylinder and the actual rotation angle of the right (or left) side wheel fed back by the displacement sensor and the rotation angle sensor. Under the joint control of the two command signals , the steering trapezoidal mechanism realizes pure rolling steering, so that the left and right wheels reach the target corner;

Step 9: Determine whether the right (or left) side wheel rotation angle is larger than the critical locking rotation angle: if it is larger, go to step 3; if not, go to step 10;

Step 10: Set the second servo proportional valve in the neutral position, the second electromagnetic reversing valve is energized, and the pilot oil of the third hydraulic control check valve and the fourth hydraulic control check valve are returned to the oil, so that the transverse tie rod stretches cylinder lock;

Step eleven: synchronously with step ten, detect the actual angle of rotation of the right (or left) side wheel of the controlled steering axle;

Step 12: Calculate the deviation between the actual rotation angle of the right (or left) side wheel and the target rotation angle;

Step 13: According to the right (or left) side wheel angle deviation signal, the controller sends an instruction signal to the first servo proportional valve to control the first servo proportional valve to work;

Step 14: The first servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the left and right steering cylinders, so that the actual rotation angle of the right (or left) side wheel is close to the target rotation angle;

Step 15: The controller adjusts the command signal in real time according to the actual rotation angle of the right (or left) side wheel fed back by the rotation angle sensor. Under the control of the command signal, the steering trapezoidal mechanism realizes steering so that the right (or left) side wheel The wheel reaches the target corner.

The critical locking rotation angle is plus or minus 5° to 15°, that is, the critical locking rotation angle to the left or right can be set to a certain value in the range of 5° to 15°.

The controller is a programmable logic controller or a single-chip microcomputer, and the response frequency of the controller is adapted to the response frequency of the first servo proportional valve and the second servo proportional valve.

Through two servo proportional valves, the electro-hydraulic servo control is performed on the lateral pull rod telescopic cylinder and the left and right steering cylinders respectively, so as to effectively ensure that the rotation angle of the bilateral wheels fully meets the Ackermann conditions required for multi-axle vehicle steering, and achieve high response and high speed. Precision pure roll steering. The electro-hydraulic servo control of the tie-rod telescopic cylinders allows for precise pure roll steering. In order to further improve the safety of the high-speed driving of the vehicle, the electro-hydraulic lock of the telescopic cylinder of the transverse tie rod can be locked, that is, the length of the telescopic cylinder of the transverse tie rod can be locked. risk of failure.

The length of the transverse tie rod of the conventional steering trapezoidal mechanism is a fixed value, and the pure rolling of the left and right side wheels cannot be realized by adjusting the length of the transverse tie rod. Generally, through the optimal design of the four-bar mechanism, the steering trapezoid approximately satisfies the angle relationship of the Ackermann trapezoid, that is, when the steering wheels on both sides are in the range of small turning angles, the deviation between the actual turning angle and the Ackermann turning angle is very small, while in the large turning angle The deviation between the actual rotation angle and the Ackermann rotation angle increases significantly in the range. Therefore, when the vehicle is running at high speed, the technical solution of the present invention locks the tie rod within a small rotation angle range, which not only ensures that the left and right side wheel rotation angles meet the Ackermann steering relationship as much as possible, but also significantly improves the safety of high-speed driving. By reasonably setting the critical locking angle value, such as setting it to plus or minus 5°~15°, that is, the steering wheel turns from the neutral position to the left (or right) by 5°~15°, and the steering angle on one side is used as the control benchmark. Finally, the critical angle is used as the dividing line, and the real-time adjustment of the telescopic cylinder of the transverse tie rod is used in a large angle range (mostly at low speeds), thereby ensuring the precise pure rolling steering of the left and right side wheels; while in a small angle range, through Lock the telescopic cylinder of the transverse tie rod to ensure the safety of high-speed driving and take into account the approximate pure rolling steering of the left and right side wheels.

In the above steering process, there is a switch between the four-bar mechanism and the five-bar mechanism, that is, the small steering range is a four-bar mechanism, and the large turning angle range is a five-bar mechanism; at the same time, there is a switching of the number of degrees of freedom, that is, the small turning angle range is a single-degree-of-freedom steering , while the large turning angle range is a two-degree-of-freedom steering. It can be seen that in the steering trapezoidal mechanism with the telescopic cylinder of the transverse tie rod, due to the control of whether the telescopic cylinder is locked or not, there will be a change in the topological structure of the steering trapezoidal mechanism and a change in the degree of freedom during the steering process. However, variable topology and variable degrees of freedom are two necessary and sufficient conditions for a metamorphic mechanism. This steering trapezoidal mechanism with a transverse tie rod telescopic cylinder can be called a metamorphic steering trapezoid, and the transverse tie rod telescopic cylinder is the metamorphic mechanism. Turn to the metamorphic part of the trapezoid. Therefore, the metamorphic steering trapezoidal mechanism creates conditions for the design of high-quality pure rolling steering mechanism.

Fig. 5 is a schematic diagram of the electro-hydraulic servo steering system applied to the pure rolling of multi-axle vehicles according to the present invention.

The electrohydraulic servo steering system of the present invention can be used in multi-axle vehicles with two (or more than two) axles. The first axle of this vehicle generally adopts steering assist methods such as mechanical type or machine-hydraulic servo, and each axle thereafter adopts the electro-hydraulic servo steering system of the present invention. For the steering axle applying the electro-hydraulic servo steering system of the present invention, the Effectively ensure that the left and right steering wheels of the bridge meet the Ackermann steering conditions required for pure rolling, and then enable the rear axles to achieve high-response and high-precision dynamic pure rolling steering.

In addition, if the first bridge also adopts the electro-hydraulic servo steering system of the present invention, the full bridge steer-by-wire can be realized. At this time, the steering wheel angle sensor converts the steering wheel angle signal into an electrical signal and inputs it to the controller. The controller calculates the target angles of all steering axles (including the first axle) according to the corresponding steering mode, and then uses the electro-hydraulic servo steering system of each axle. Precise control. This effectively ensures that the left and right steering wheels of all steering axles meet the Ackermann steering conditions required for pure rolling, thereby enabling the full axle to achieve high-response and high-precision dynamic pure rolling steering.

The electro-hydraulic servo steering system of each bridge can be uniformly supplied by the hydraulic pump and returned to the oil tank, that is, the electro-hydraulic servo steering system of the above-mentioned bridges is connected in parallel, and the oil inlet line is connected to the outlet of the hydraulic pump 2, and the oil is returned to the oil tank. The road is connected back to the oil tank 1 in parallel.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (8)

1. An electro-hydraulic servo steering system for pure rolling of multi-axle vehicles, said multi-axle vehicle comprises a first axle and each steering axle at the rear, and the electro-hydraulic servo steering system for each steering axle at the rear comprises a fuel tank (1 ), hydraulic pump (2), first servo proportional valve (4), vehicle frame (16), left power steering cylinder (9) and right power steering cylinder (14); rod cavity of left power steering cylinder (9) and the rodless chamber of the right power steering cylinder (14) form the first working oil circuit (R1), the rodless chamber of the left steering power cylinder (9) and the rod chamber of the right steering power cylinder (14) form the second working oil Road (R2), the first working oil circuit (R1) and the second working oil circuit (R2) are respectively connected to the A and B working oil ports of the first servo proportional valve (4); It is characterized in that: the electro-hydraulic servo steering system includes a transverse pull rod telescopic cylinder (12), a second servo proportional valve (22) and an electronic control system; The piston part of the telescopic rod cylinder (12) is hinged to the first trapezoidal arm (10) on one side, and the cylinder part of the telescopic rod cylinder (12) is hinged to the second trapezoidal arm (13) on the other side; The two working chambers of the transverse rod telescopic cylinder (12) are respectively connected with the A and B working oil ports of the second servo proportional valve (22), respectively forming the third working oil circuit (R3) and the fourth working oil circuit (R4 ); the P ports of the first servo proportional valve (4) and the second servo proportional valve (22) are connected to the oil inlet circuit, and the T ports of the first servo proportional valve (4) and the second servo proportional valve (22) Both are connected to the oil tank (1); the system also includes the first hydraulic control check valve (5), the second hydraulic control check valve (6), the third hydraulic control check valve (19) and the fourth hydraulic control check valve The check valve (20) is connected in series with the four oil circuits of the first working oil circuit (R1), the second working oil circuit (R2), the third working oil circuit (R3) and the fourth working oil circuit (R4). on the road; The pilot oil of the first hydraulic control check valve (5) and the second hydraulic control check valve (6) is controlled by the first electromagnetic reversing valve (3); the third hydraulic control check valve (19) and the pilot oil of the fourth hydraulic control check valve (20) are controlled by the second electromagnetic reversing valve (23); the first electromagnetic reversing valve (3) and the second electromagnetic reversing valve ( 23) Both are two-position three-way valves; The electronic control system is used to calculate the target length of the telescopic cylinder of the transverse tie rod according to the target rotation angles of the left and right wheels of the controlled steering axle, and send it to the second servo proportional valve in the electro-hydraulic servo steering system where the controlled steering axle is located, output a command signal corresponding to the target length of the transverse rod telescopic cylinder; at the same time, output a signal corresponding to the right or left wheel to the first servo proportional valve in the electro-hydraulic servo steering system where the controlled steering axle is located. The command signal corresponding to the target rotation angle, and adjust the command signals in real time according to the displacement feedback signal of the lateral tie rod telescopic cylinder of the controlled steering axle and the feedback rotation angle signal of the right or left wheel. 2. An electro-hydraulic servo steering system for pure rolling of multi-axle vehicles according to claim 1, characterized in that: the telescopic rod cylinder (12) is a double-rod cylinder, and the two sides of the telescopic cylinder The effective working area of the rod cavity is equal. 3. An electro-hydraulic servo steering system for pure rolling of multi-axle vehicles according to claim 1, characterized in that: the system also includes a first oil supplement overflow valve group (7), a second oil supplement overflow valve group The valve group (8), the third charge oil relief valve group (17) and the fourth charge oil relief valve group (18) are respectively connected in series to the first working oil circuit (R1) and the second working oil circuit ( R2), the third working oil circuit (R3), and the fourth working oil circuit (R4) on four oil circuits. 4. An electro-hydraulic servo steering system for pure rolling of multi-axle vehicles according to claim 3, characterized in that: the first supplementary oil relief valve group (7), the second supplementary oil relief valve group (8 ), the third charge relief valve group (17) and the fourth charge relief valve group (18) have the same structure, each of which includes a relief valve (24) and a check valve (25), and The one-way valve (25) is connected in parallel with the overflow valve (24). 5. The electro-hydraulic servo steering system for pure rolling of multi-axle vehicles according to claim 1, characterized in that the electronic control system includes: a controller (21) for detecting the right or left side of the steering axle A rotation angle sensor (15) for the wheel rotation angle, a displacement sensor (11) for detecting the length of the telescopic cylinder of the transverse tie rod, a first electromagnetic reversing valve (3) and a second electromagnetic reversing valve (23); The controller (21) is electrically connected to the first servo proportional valve (4), the second servo proportional valve (22), the rotation angle sensor (15), the displacement sensor (11), the first electromagnetic reversing valve (3) and the second Solenoid reversing valve (23); Among them, the controller (21), the second servo proportional valve (22), the telescopic cylinder (12) and the displacement sensor (11) form a closed-loop control for the length of the telescopic cylinder; at the same time, the controller (21), the first servo The proportional valve (4), the right steering assist cylinder (14), the left steering assist cylinder (9) and the right or left rotation angle sensor (15) form a closed-loop control for the rotation angle of the right or left wheel. 6. A steering control method applicable to an electro-hydraulic servo steering system for pure rolling of a multi-axle vehicle according to claim 1, characterized in that it comprises the following steps: Step 1: The electro-hydraulic servo steering system inputs the target angle signals of the left and right wheels of the controlled steering axle to the controller of the steering axle; Step 2: Determine whether it is necessary to lock the telescopic rod telescopic cylinder within the critical locking angle range on the left and right sides of the center of the steering wheel: if not, skip to step 3; if necessary, skip to step 9; Step 3: The controller calculates the target length of the telescopic cylinder of the transverse tie rod according to the target rotation angle signals of the left and right wheels, and uses the target length and the target rotation angle of the right or left wheel as two control targets to control the system; Step 4: Detect the actual length of the telescopic cylinder of the transverse tie rod of the controlled steering axle and the actual rotation angle of the right or left wheel; Step 5: Calculate the deviation between the actual length of the telescopic cylinder of the transverse rod and the target length, and calculate the deviation between the actual rotation angle of the right or left wheel and the target rotation angle; Step 6: According to the length deviation signal of the transverse rod telescopic cylinder, the controller sends the first command signal to the second servo proportional valve to control the operation of the second servo proportional valve; at the same time, according to the right or left wheel angle deviation signal, the first servo The proportional valve sends the second command signal to control the first servo proportional valve to work; Step 7: The second servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the telescopic rod cylinder, so that the actual length of the telescopic cylinder is close to the target length. The first servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the left and right steering cylinders, so that the right Or the actual turning angle of the left wheel is close to the target turning angle; Step 8: The controller adjusts the two command signals in real time according to the actual length of the telescopic rod telescopic cylinder fed back by the displacement sensor and the rotation angle sensor and the actual rotation angle of the right or left wheel. Under the joint control of the two command signals, the steering The trapezoidal mechanism realizes pure rolling steering, making the left and right wheels reach the target turning angle; Step 9: Determine whether the right or left wheel rotation angle is greater than the critical locking angle: if it is greater, go to step 3; if not, go to step 10; Step 10: Set the second servo proportional valve in the neutral position, the second electromagnetic reversing valve is energized, and the pilot oil of the third hydraulic control check valve and the fourth hydraulic control check valve are returned to the oil, so that the transverse tie rod stretches cylinder lock; Step 11: Synchronously with step 10, detect the actual rotation angle of the right or left wheel of the controlled steering axle; Step 12: Calculate the deviation between the actual rotation angle of the right or left wheel and the target rotation angle; Step 13: According to the right or left wheel angle deviation signal, the controller sends a command signal to the first servo proportional valve to control the first servo proportional valve to work; Step 14: The first servo proportional valve outputs a hydraulic signal to control the expansion and contraction of the left and right steering cylinders, so that the actual rotation angle of the right or left wheel is close to the target rotation angle; Step 15: The controller adjusts the command signal in real time according to the actual rotation angle of the right or left wheel fed back by the rotation angle sensor. Under the control of the command signal, the steering trapezoidal mechanism realizes the steering, so that the right or left wheel reaches the target rotation angle . 7. A steering control method according to claim 6, characterized in that: said critical locking rotation angle is plus or minus 5°~15°. 8. A steering control method according to claim 6, characterized in that: the controller (21) is a programmable logic controller or a single-chip microcomputer, and the response frequency of the controller is proportional to the first servo ratio The response frequency of the valve (4) and the second servo proportional valve (22) match, and the response frequency of the first servo proportional valve (4) and the second servo proportional valve (22) at 5% spool displacement is not less than 40Hz, the response frequency under 100% spool displacement is not less than 20Hz.