Forklift truck steering control system

Abstract

The application relates to a forklift steering control system, which comprises a front axle steering mechanism, a rear axle steering mechanism, a mode switching valve group, a steering gear, an oil tank and a system controller; the front axle steering mechanism comprises a front steering oil cylinder, and the rear axle steering mechanism comprises a rear steering oil cylinder; the mode switching valve group is provided with P1 and T1 which are connected with the steering gear, P2 and T2 which are connected with the front steering oil cylinder, A1 and B1 which are connected with the rear steering oil cylinder, and A2 which is connected with the oil tank; the mode switching valve group comprises two two-position four-way electromagnetic switching valves, a three-position four-way electromagnetic switching valve, a bidirectional hydraulic lock and four two-position three-way hydraulic control switching valves which are communicated through oil paths. The forklift steering control system can be compatible with a conventional front wheel steering system, realizes three steering modes of front wheel steering, four wheel steering and crab-shaped walking, and the front steering oil cylinder is always a driving oil cylinder, the rear steering oil cylinder is always a driven oil cylinder, and the pressure of the rear wheel rotation can be guaranteed.

Description

Technical Field

[0001] This invention relates to forklifts, and more particularly to a forklift steering control system, especially a telescopic boom forklift steering control system. Background Technology

[0002] Currently, forklifts in use are mainly divided into counterbalanced forklifts and telescopic forklifts. Counterbalanced forklifts generally only have a rear-wheel steering mode; telescopic forklifts generally have three steering modes: front-wheel steering, four-wheel steering, and crab-like movement. The hydraulic circuits for these three steering modes are reversible, meaning that when turning left, the front steering cylinder is the driving cylinder and the rear steering cylinder is the driven cylinder; conversely, when turning right, the rear steering cylinder is the driving cylinder and the front steering cylinder is the driven cylinder. The biggest drawback of this control method is that when the vehicle has another front-wheel steering system, insufficient pressure may occur when the rear steering cylinder is acting as the driving cylinder, preventing the rear wheels from turning. Therefore, the existing forklift steering control system urgently needs improvement.

[0003] CN113460917A discloses a "multi-mode valve for telescopic boom forklifts and an automatic locking multi-mode steering system." The multi-mode valve includes a housing, and a valve core, electromagnets A, B, and C disposed within the housing. Two limiting grooves are sequentially arranged on the side wall of the valve core. Electromagnets A and B are respectively located at both ends of the valve core, used to control the valve core's movement towards electromagnet A or B. Electromagnet C is located on the side of the valve core and connected to the housing via an elastic element, cooperating with the limiting grooves on the valve core's side wall to lock the valve core. It incorporates a self-locking function; in an emergency, the mode will not change autonomously in the self-locking state, resulting in higher safety performance.

[0004] CN217892990U discloses a "Forklift Steering Control System and Control Device," belonging to the field of forklift technology. It includes a control valve connected to an oil tank. The control valve comprises a first solenoid valve, a second solenoid valve, and a third solenoid valve. The first solenoid valve is connected to both the second and third solenoid valves, and the second and third solenoid valves are connected to a steering cylinder. In automatic driving mode, the first solenoid valve controls the flow of hydraulic oil to the second and third solenoid valves, thereby controlling the forklift's steering. The forklift steering control system and control device provided by this utility model can freely switch between automatic and manual driving modes for forklift steering control. It is highly practical, widely applicable, and can be used in the control of unmanned forklifts. The switching is convenient and smooth, greatly improving the forklift's working efficiency.

[0005] Undoubtedly, the technical solutions disclosed in both patent documents represent a valuable attempt in their respective technical fields. Summary of the Invention

[0006] The purpose of this invention is to provide a forklift steering control system that is compatible with conventional front wheel steering systems, enabling three steering modes: front wheel steering, four-wheel steering, and crab-like walking. Furthermore, the front steering cylinder is always the driving cylinder, and the rear steering cylinder is always the driven cylinder, ensuring the pressure for rear wheel rotation.

[0007] The present invention discloses a forklift steering control system, comprising a front axle steering mechanism, a rear axle steering mechanism, a mode switching valve group, a steering gear, an oil tank, and a system controller; the front axle steering mechanism includes a front steering cylinder positioned and connected to the front axle housing, and the rear axle steering mechanism includes a rear steering cylinder positioned and connected to the rear axle housing; the mode switching valve group is provided with P1 and T1 ports connected to the steering gear, P2 and T2 ports connected to the front steering cylinder, A1 and B1 ports connected to the rear steering cylinder, and A2 port connected to the oil tank; the mode switching valve group includes two two-position four-way solenoid directional valves, one three-position four-way solenoid directional valve, one bidirectional hydraulic lock, and four two-position three-way hydraulic control directional valves connected by an oil circuit; it can change the flow direction of fluid through each solenoid directional valve, each hydraulic control directional valve, and the bidirectional hydraulic lock to achieve front wheel steering, four-wheel steering, and crab-like walking functions.

[0008] Furthermore, the two two-position four-way solenoid directional valves are a first solenoid directional valve and a second solenoid directional valve; the first solenoid directional valve has two switching positions, one solenoid D2, and four ports: namely, port A, port B, port P, and port T; the solenoid D2 is located at the right end of the valve body of the first solenoid directional valve; ports P and T of the first solenoid directional valve correspond to and are connected to ports P2 and T2 of the mode switching valve group, respectively; ports A and B of the first solenoid directional valve are both connected to the oil tank; the second solenoid directional valve has two switching positions, one solenoid D1, and four ports: namely, port A, port B, port P, and port T; the solenoid D1 is located at the right end of the valve body of the second solenoid directional valve; ports P and T of the second solenoid directional valve correspond to and are connected to ports P1 and T1 of the mode switching valve group, respectively.

[0009] Furthermore, one of the three-position four-way solenoid directional valves is a third solenoid directional valve, which has three switching positions, two solenoids D3 and D4, and four ports: namely, port A, port B, port P, and port T; solenoid D3 is located at the left end of the valve body of the third solenoid directional valve, and solenoid D4 is located at the right end of the valve body of the third solenoid directional valve; ports A and B of the third solenoid directional valve are respectively connected to ports A1 and B1 of the mode switching valve group via bidirectional hydraulic locks.

[0010] Furthermore, the four two-position three-way hydraulic directional valves are the first hydraulic directional valve, the second hydraulic directional valve, the third hydraulic directional valve, and the fourth hydraulic directional valve. Each of them has two switching positions and four oil ports: namely, oil port P, oil port A, oil port B, and control cylinder K.

[0011] The oil port P of the first hydraulic directional valve is connected to the oil port A of the second solenoid directional valve. The oil port A of the first hydraulic directional valve is connected to the oil port T of the first solenoid directional valve and the T2 port of the mode switching valve group. The oil port B of the first hydraulic directional valve is connected to the oil port B of the second hydraulic directional valve. The control oil port K of the first hydraulic directional valve is connected to the oil port B of the second solenoid directional valve.

[0012] The oil port A of the second hydraulic directional valve is connected to the oil port P of the first solenoid directional valve, the oil port P of the second hydraulic directional valve is connected to the oil port P of the third solenoid directional valve, and the control oil port K of the second hydraulic directional valve is connected to the oil port B of the second solenoid directional valve.

[0013] The oil port P of the third hydraulic directional valve is connected to the oil port T of the third solenoid directional valve, the oil port B of the third hydraulic directional valve is connected to the T2 port of the mode switching valve group, the oil port A of the third hydraulic directional valve is connected to the oil port A of the fourth hydraulic directional valve, and the control oil port K of the third hydraulic directional valve is connected to the oil port B of the second solenoid directional valve.

[0014] The oil port P of the fourth hydraulic directional valve is connected to the oil port B of the second solenoid directional valve, the oil port B of the fourth hydraulic directional valve is connected to the oil port P of the first solenoid directional valve, and the control oil port K of the fourth hydraulic directional valve is connected to the oil port B of the second solenoid directional valve.

[0015] Furthermore, the steering gear is provided with a steering oil circuit, wherein the right turn oil port is connected to the P1 port of the mode switching valve group, and the left turn oil port is connected to the T1 port of the mode switching valve group.

[0016] Furthermore, the system controller is equipped with three steering mode switches: "front wheel steering", "four-wheel steering" and "crab walk"; the system controller is electrically connected to the first electromagnetic reversing valve, the second electromagnetic reversing valve and the third electromagnetic reversing valve.

[0017] Furthermore, both the front steering cylinder and the rear steering cylinder are double-acting double-piston rod cylinders, and their cylinder diameter, rod diameter, and stroke are exactly the same.

[0018] Furthermore, the front axle steering mechanism also includes two front wheels, which are respectively hinged to both ends of the front steering cylinder via steering arms.

[0019] Furthermore, the rear axle steering mechanism also includes two rear wheels, which are respectively hinged to both ends of the rear steering cylinder via steering arms.

[0020] Beneficial technical effects of the present invention:

[0021] Since this steering control system consists of a front steering cylinder, a rear steering cylinder, and a steering mode switching valve group, the design of the cylinders can achieve a large moving thrust; it can steer the front wheels, and can achieve simultaneous counter-rotation of the front and rear wheels (i.e., four-wheel steering), and can achieve simultaneous rotation of the front and rear wheels in the same direction (i.e., crab-like movement).

[0022] Due to the design of the hydraulic circuit, when turning left or right, the front steering cylinder is always the driving cylinder and the rear steering cylinder is the driven cylinder.

[0023] Because the front steering cylinder and the rear steering cylinder are connected in series, the front steering cylinder and the rear steering cylinder can move synchronously.

[0024] Because this steering control system is compatible with other steering systems, it can be completely disconnected when not in use, reducing steering load.

[0025] In summary, this invention can achieve front-wheel steering, four-wheel steering, and crab-like movement; it features that the front steering cylinder is always the driving cylinder and the rear steering cylinder is always the driven cylinder; it also has the feature of being compatible with other steering systems. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the working principle of the present invention.

[0027] In the diagram (the markings refer to the technical features):

[0028] 1—Front axle steering mechanism; 10—Front steering cylinder; 11—Front wheel;

[0029] 2—Rear axle steering mechanism; 20—Rear steering cylinder; 21—Rear wheel;

[0030] 3—Mode switching valve group, 31—First solenoid directional valve, 32—Second solenoid directional valve, 33—Third solenoid directional valve, 34—Two-way hydraulic lock, 35—First hydraulic directional valve, 36—Second hydraulic directional valve, 37—Third hydraulic directional valve, 38—Fourth hydraulic directional valve;

[0031] 4—Steering gear, 41—Right turn port, 42—Left turn port;

[0032] 5—Fuel tank. Detailed Implementation

[0033] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments:

[0034] See Figure 1 The forklift steering control system shown includes a front axle steering mechanism 1, a rear axle steering mechanism 2, a mode switching valve group 3, a steering gear 4, an oil tank 5, and a system controller (not labeled in the figure). The front axle steering mechanism 1 includes a front steering cylinder 10 positioned and connected to the front axle housing, and the rear axle steering mechanism 2 includes a rear steering cylinder 20 positioned and connected to the rear axle housing. The mode switching valve group 3 is provided with a P1 port and a T1 port that communicate with the steering gear 4 and is connected to the front steering cylinder 10. The system includes interconnected ports P2 and T2, ports A1 and B1 connected to the rear steering cylinder 20, and port A2 connected to the oil tank 5; the mode switching valve group 3 includes two two-position four-way solenoid directional valves, one three-position four-way solenoid directional valve, one two-way hydraulic lock 34, and four two-position three-way hydraulic control directional valves connected by an oil circuit; it can change the flow direction of fluid through each solenoid directional valve, each hydraulic control directional valve, and the two-way hydraulic lock to achieve the functions of front wheel steering, four-wheel steering, and crab-like walking.

[0035] The two two-position four-way solenoid directional valves are a first solenoid directional valve 31 and a second solenoid directional valve 32. The first solenoid directional valve 31 has two switching positions, one solenoid D2, and four ports: port A, port B, port P, and port T. The solenoid D2 is located at the right end of the valve body of the first solenoid directional valve 31. Initially, the valve core of the first solenoid directional valve 31 is in the left position, at which time port P is connected to port A, and port B is connected to port T. When the valve core is in the right position, all four ports are not connected.

[0036] The oil port P and oil port T of the first electromagnetic reversing valve 31 correspond to and are connected to the P2 port and T2 port of the mode switching valve group 3, respectively; the oil port A and oil port B of the first electromagnetic reversing valve 31 are both connected to the oil tank 5.

[0037] The second electromagnetic directional valve 32 has two switching positions, one electromagnet D1, and four oil ports: namely, oil port A, oil port B, oil port P, and oil port T; the electromagnet D1 is located at the right end of the valve body of the second electromagnetic directional valve 32; initially, the valve core of the second electromagnetic directional valve 32 is in the left position, at which time, the four oil ports are not connected; when the valve core is in the right position, oil port P is connected to oil port B, and oil port A is connected to oil port T;

[0038] The oil port P and oil port T of the second electromagnetic reversing valve 32 correspond to and are connected to the P1 port and T1 port of the mode switching valve group 3, respectively.

[0039] One of the three-position four-way solenoid directional valves is a third solenoid directional valve 33, which has three switching positions, two solenoids D3 and D4, and four ports: port A, port B, port P, and port T. Solenoid D3 is located at the left end of the valve body of the third solenoid directional valve 33, and solenoid D4 is located at the right end of the valve body of the third solenoid directional valve 33. Initially, the valve core of the third solenoid directional valve 33 is in the middle position, at which time port P and port T are connected, and port A and port B are not connected. When the valve core is in the left position, port P and port A are connected, and port B and port T are connected. When the valve core is in the right position, port P and port B are connected, and port A and port T are connected. Ports A and B of the third solenoid directional valve 33 are respectively connected to ports A1 and B1 of the mode switching valve group 3 via a bidirectional hydraulic lock 34.

[0040] The four two-position three-way hydraulic control directional valves are the first hydraulic control directional valve 35, the second hydraulic control directional valve 36, the third hydraulic control directional valve 37, and the fourth hydraulic control directional valve 38. Each of them has two switching positions and four oil ports: namely, oil port P, oil port A, oil port B, and control oil port K.

[0041] The oil port P of the first hydraulic directional valve 35 is connected to the oil port A of the second solenoid directional valve 32. The oil port A of the first hydraulic directional valve 35 is connected to the oil port T of the first solenoid directional valve 31 and the T2 port of the mode switching valve group 3. The oil port B of the first hydraulic directional valve 35 is connected to the oil port B of the second hydraulic directional valve 36. The control oil port K of the first hydraulic directional valve 35 is connected to the oil port B of the second solenoid directional valve 32.

[0042] The oil port A of the second hydraulic directional valve 36 is connected to the oil port P of the first solenoid directional valve 31, the oil port P of the second hydraulic directional valve 36 is connected to the oil port P of the third solenoid directional valve 33, and the control oil port K of the second hydraulic directional valve 36 is correspondingly connected to the oil port B of the second solenoid directional valve 32.

[0043] The oil port P of the third hydraulic directional valve 37 is connected to the oil port T of the third electromagnetic directional valve 33, the oil port B of the third hydraulic directional valve 37 is connected to the T2 port of the mode switching valve group 3, the oil port A of the third hydraulic directional valve 37 is connected to the oil port A of the fourth hydraulic directional valve 38, and the control oil port K of the third hydraulic directional valve 37 is correspondingly connected to the oil port B of the second electromagnetic directional valve 32.

[0044] The oil port P of the fourth hydraulic directional valve 38 is connected to the oil port B of the second solenoid directional valve 32, the oil port B of the fourth hydraulic directional valve 38 is connected to the oil port P of the first solenoid directional valve 31, and the control oil port K of the fourth hydraulic directional valve 38 is correspondingly connected to the oil port B of the second solenoid directional valve 32.

[0045] The steering gear 4 is provided with a steering oil circuit, with its right turn oil port 41 connected to the P1 oil port of the mode switching valve group 3 and its left turn oil port 42 connected to the T1 port of the mode switching valve group 3.

[0046] The system controller is equipped with three steering mode switches: "front wheel steering", "four-wheel steering" and "crab walk"; the system controller is electrically connected to the first electromagnetic reversing valve 31, the second electromagnetic reversing valve 32 and the third electromagnetic reversing valve 33.

[0047] Both the front steering cylinder 10 and the rear steering cylinder 20 are double-acting double-piston rod cylinders, and their cylinder diameter, rod diameter, and stroke are exactly the same.

[0048] The front axle steering mechanism 1 also includes two front wheels 11, which are respectively hinged to the two ends of the front steering cylinder 10 via steering arms.

[0049] The rear axle steering mechanism 2 also includes two rear wheels 21, which are respectively hinged to the two ends of the rear steering cylinder 20 via steering arms.

[0050] The following is combined with Figure 1 The functions of the present invention will be described one by one with the examples.

[0051] Example 1: Compatible with other steering systems; In the initial state, the first solenoid directional valve 31, the second solenoid directional valve 32, and the third solenoid directional valve 33 are not energized. At this time, the valve core of the second solenoid directional valve 32 is in the left position, which will cut off the oil supply to the system; the valve core of the first solenoid directional valve 31 is in the left position, and the left and right chambers of the front steering cylinder 10 are connected to the oil tank 5; at this time, the forklift can perform front wheel steering under the action of other steering systems, and this system will not generate additional load.

[0052] Example 2: Front wheel steering; Set the steering mode switch of the system controller to the "front wheel steering" position, so that the electromagnet D2 of the first solenoid directional valve 31 and the electromagnet D1 of the second solenoid directional valve 32 are energized, while the electromagnets D3 and D4 of the third solenoid directional valve 33 are de-energized; at this time, the valve core of the first solenoid directional valve 31 is in the right position, the valve core of the second solenoid directional valve 32 is in the right position, and the valve core of the third solenoid directional valve 33 is in the middle position.

[0053] When turning left: High-pressure oil in steering gear 4 enters from port T1 of mode switching valve group 3, first flowing from port T of the second solenoid directional valve 32 to port A; at this time, the control ports K of the first hydraulic directional valve 35, the second hydraulic directional valve 36, the third hydraulic directional valve 37, and the fourth hydraulic directional valve 38 are not affected by high-pressure oil. The second hydraulic directional valve 36 and the third hydraulic directional valve 37 are in the left position, and the first hydraulic directional valve 35 and the fourth hydraulic directional valve 38 are in the upper position; high-pressure oil flows from port P of the first hydraulic directional valve 35 to port A, and then enters the front steering cylinder 10 from port T2 of mode switching valve group 3. Right chamber; high-pressure oil pushes the piston rod of the front steering cylinder 10 to the left, causing the front wheel 11 to turn left; the hydraulic oil in the left chamber of the front steering cylinder 10 is pushed out and enters from port P2 of the mode switching valve group 3, flows from port A of the second hydraulic directional valve 36 to port P, then flows from port P of the third solenoid directional valve 33 to port T, then flows from port P of the third hydraulic directional valve 37 to port A, then flows from port A of the fourth hydraulic directional valve 38 to port P, then flows from port B of the second solenoid directional valve 32 to port P, and finally flows out from port P1 of the mode switching valve group 3 and flows back to the oil tank 5 through the steering gear 4.

[0054] When turning right: High-pressure oil in steering gear 4 enters from port P1 of mode switching valve group 3, first flowing from port P of the second solenoid directional valve 32 to port B; at this time, high-pressure oil is applied to the control ports K of the first hydraulic directional valve 35, the second hydraulic directional valve 36, the third hydraulic directional valve 37, and the fourth hydraulic directional valve 38. The first hydraulic directional valve 35 and the fourth hydraulic directional valve 38 are in the lower position under the action of high-pressure oil, while the second hydraulic directional valve 36 and the third hydraulic directional valve 37 are in the right position under the action of high-pressure oil; high-pressure oil flows from port P of the fourth hydraulic directional valve 38 to port B, and then enters from port P2 of mode switching valve group 3. The high-pressure oil enters the left chamber of the front steering cylinder 10; the high-pressure oil pushes the piston rod of the front steering cylinder 10 to move to the right, causing the front wheel to turn to the right; the hydraulic oil in the right chamber of the front steering cylinder 10 is pushed out and enters from the T2 port of the mode switching valve group 3, flows from the oil port B of the third hydraulic control directional valve 37 to the oil port P, then flows from the oil port T of the third solenoid directional valve 33 to the oil port P, then flows from the oil port P of the second hydraulic control directional valve 36 to the oil port B, then flows from the oil port B of the first hydraulic control directional valve 35 to the oil port P, then flows from the oil port A of the second solenoid directional valve 32 to the oil port T, and finally flows out from the T1 port of the mode switching valve group 3 and flows back to the oil tank 5 through the steering gear 4.

[0055] Example 3: Four-wheel steering; Set the steering mode switch of the system controller to the "four-wheel steering" position, so that the electromagnet D2 of the first solenoid directional valve 31, the electromagnet D1 of the second solenoid directional valve 32, and the electromagnet D4 of the third solenoid directional valve 33 are energized, while D3 is de-energized; at this time, the valve core of the first solenoid directional valve 31, the valve core of the second solenoid directional valve 32, and the valve core of the third solenoid directional valve 33 are all in the right position.

[0056] When turning left: High-pressure oil in steering gear 4 enters from port T1 of mode switching valve group 3, first flowing from port T of the second solenoid directional valve 32 to port A. At this time, there is no high-pressure oil action at the control ports K of the first hydraulic directional valve 35, the second hydraulic directional valve 36, the third hydraulic directional valve 37, and the fourth hydraulic directional valve 38. The second hydraulic directional valve 36 and the third hydraulic directional valve 37 are in the left position, and the first hydraulic directional valve 35 and the fourth hydraulic directional valve 38 are in the upper position. High-pressure oil flows from port P of the first hydraulic directional valve 35 to port A, and then enters the right chamber of the front steering cylinder 10. The high-pressure oil pushes the piston rod of the front steering cylinder 10 to move to the left, causing the front wheel 11 to turn left. The hydraulic oil in the left chamber of the front steering cylinder 10 is pushed out and enters from port P2 of mode switching valve group 3, and flows through the second hydraulic directional valve. The oil flows from port A of 36 to port P, then from port P of the third solenoid directional valve 33 to port B, and then through the bidirectional hydraulic lock 34, it flows out from port B1 of the mode switching valve group 3 and enters the left chamber of the rear steering cylinder 20. The high-pressure oil pushes the piston rod of the rear steering cylinder 20 to the right, causing the rear wheel 21 to turn right. The hydraulic oil in the right chamber of the rear steering cylinder 20 is pushed out and enters through port A1 of the mode switching valve group 3. Then, through the bidirectional hydraulic lock 34, it flows from port A of the third solenoid directional valve 33 to port T, then from port P of the third hydraulic directional valve 37 to port A, then from port A of the fourth hydraulic directional valve 38 to port P, then from port B of the second solenoid directional valve 32 to port P, and finally flows out from port P1 of the mode switching valve group 3 and flows back to the oil tank 5 through the steering gear 4.

[0057] When turning right: High-pressure oil in steering gear 4 enters from port P1 of mode switching valve group 3, first flowing from port P of the second solenoid directional valve 32 to port B. At this time, high-pressure oil acts on the control ports K of the first hydraulic directional valve 35, the second hydraulic directional valve 36, the third hydraulic directional valve 37, and the fourth hydraulic directional valve 38. Under the action of high-pressure oil, the first hydraulic directional valve 35 and the fourth hydraulic directional valve 38 are in the lower position, while the second hydraulic directional valve 36 and the third hydraulic directional valve 37 are in the right position. High-pressure oil flows from port P of the fourth hydraulic directional valve 38 to port B, and then enters the left chamber of the front steering cylinder 10. The high-pressure oil pushes the piston rod of the front steering cylinder 10 to move to the right, causing the front wheel 11 to turn right. The hydraulic oil in the right chamber of the front steering cylinder 10 is pushed out and enters from port T2 of mode switching valve group 3. The oil flows from port B of the third hydraulic directional valve 37 to port P, then from port T of the third solenoid directional valve 33 to port A. Afterwards, it flows out through port A1 of the mode switching valve group 3 via the bidirectional hydraulic lock 34 and enters the right chamber of the rear steering cylinder 20. The high-pressure oil pushes the piston rod of the rear steering cylinder 20 to the left, causing the rear wheel 21 to turn left. The hydraulic oil in the left chamber of the rear steering cylinder 20 is pushed out and enters through port B1 of the mode switching valve group 3. Then, it flows from port B of the third solenoid directional valve 33 to port P via the bidirectional hydraulic lock 34, then from port P of the second hydraulic directional valve 36 to port B, then from port B of the first hydraulic directional valve 35 to port P, then from port A of the second solenoid directional valve 32 to port T, and finally flows out through port T1 of the mode switching valve group 3 and returns to the oil tank 5 via the steering gear 4.

[0058] Example 4: Crab-like movement; Set the steering mode switch of the system controller to the "crab-like movement" position, energizing electromagnet D2 of the first solenoid directional valve 31 and electromagnet D1 of the second solenoid directional valve 32, energizing electromagnet D3 of the third solenoid directional valve 33, and de-energizing electromagnet D4. At this time, the valve core of the first solenoid directional valve 31 is in the right position, the valve core of the second solenoid directional valve 32 is in the right position, and the valve core of the third solenoid directional valve 33 is in the left position.

[0059] When turning left: High-pressure oil in steering gear 4 enters from port T1 of mode switching valve group 3, first flowing from port T of the second solenoid directional valve 32 to port A. At this time, there is no high-pressure oil action at the control ports K of the first hydraulic directional valve 35, the second hydraulic directional valve 36, the third hydraulic directional valve 37, and the fourth hydraulic directional valve 38. The second hydraulic directional valve 36 and the third hydraulic directional valve 37 are in the left position, and the first hydraulic directional valve 35 and the fourth hydraulic directional valve 38 are in the upper position. High-pressure oil flows from port P of the first hydraulic directional valve 35 to port A, and then enters the right chamber of the front steering cylinder 10. The high-pressure oil pushes the piston rod of the front steering cylinder 10 to move to the left, causing the front wheel 11 to turn left. The hydraulic oil in the left chamber of the front steering cylinder 10 is pushed out and enters from port P2 of mode switching valve group 3, and is controlled by the second hydraulic directional valve. The oil flows from port A of valve 36 to port P, then from port P of the third solenoid directional valve 33 to port A. Afterwards, it flows out through port A1 of the mode switching valve group 3 via hydraulic lock 11 and enters the right chamber of the rear steering cylinder 20. The high-pressure oil pushes the piston rod of the rear steering cylinder 20 to the left, causing the rear wheel to turn left. The hydraulic oil in the left chamber of the rear steering cylinder 20 is pushed out and enters through port B1 of the mode switching valve group 3. Then, it flows from port B of the third solenoid directional valve 33 to port T via bidirectional hydraulic lock 34. Afterwards, it flows from port P of the third hydraulic directional valve 37 to port A. Then, it flows from port A of the fourth hydraulic directional valve 38 to port P. Afterwards, it flows from port B of the second solenoid directional valve 32 to port P. Finally, it flows out through port P1 of the mode switching valve group 3 and returns to the oil tank 5 via the steering gear 4.

[0060] When turning right: High-pressure oil in steering gear 4 enters from port P1 of mode switching valve group 3, first flowing from port P of the second solenoid directional valve 32 to port B. At this time, high-pressure oil acts on the control ports K of the first hydraulic directional valve 35, the second hydraulic directional valve 36, the third hydraulic directional valve 37, and the fourth hydraulic directional valve 38. The first hydraulic directional valve 35 and the fourth hydraulic directional valve 38 are in the lower position under the action of high-pressure oil, while the second hydraulic directional valve 36 and the third hydraulic directional valve 37 are in the right position under the action of high-pressure oil. High-pressure oil flows from port P of the first hydraulic directional valve 35 to port B, and then enters the left chamber of the front steering cylinder 10. The high-pressure oil pushes the piston rod of the front steering cylinder 10 to move to the right, causing the front wheel 11 to turn right. The hydraulic oil in the right chamber of the front steering cylinder 10 is pushed out and enters from port T2 of mode switching valve group 3. The oil flows from port B of the third hydraulic directional valve 37 to port P, then from port T of the third solenoid directional valve 33 to port B. Afterwards, it flows out from port B1 of the mode switching valve group 3 via the bidirectional hydraulic lock 34 and enters the left chamber of the rear steering cylinder 20. The high-pressure oil pushes the piston rod of the rear steering cylinder 20 to the right, causing the rear wheel 21 to turn right. The hydraulic oil in the right chamber of the rear steering cylinder 20 is pushed out and enters from port A1 of the mode switching valve group 3. Then, it flows from port A of the third solenoid directional valve 33 to port P via the bidirectional hydraulic lock 34. Next, it flows from port P of the second hydraulic directional valve 36 to port B, then from port B of the first hydraulic directional valve 35 to port P, then from port A of the second solenoid directional valve 32 to port T. Finally, it flows out from port T1 of the mode switching valve group 3 and returns to the oil tank 5 via the steering gear 4.

Claims

1. A forklift truck steering control system comprising a front axle steering mechanism (1), a rear axle steering mechanism (2), a mode switching valve group (3), a steering gear (4), a tank (5) and a system controller, characterized in that: The front axle steering mechanism (1) comprises a front steering oil cylinder (10) connected to the front axle housing, and the rear axle steering mechanism (2) comprises a rear steering oil cylinder (20) connected to the rear axle housing; the mode switching valve group (3) is provided with P1 and T1 ports connected to the steering gear (4), P2 and T2 ports connected to the front steering oil cylinder (10), A1 and B1 ports connected to the rear steering oil cylinder (20), and A2 port connected to the oil tank (5); the mode switching valve group (3) comprises two two-position four-way electromagnetic reversing valves, one three-position four-way electromagnetic reversing valve, one bidirectional hydraulic lock (34) and four two-position three-way hydraulic control reversing valves; the flow direction of the fluid can be changed through each electromagnetic reversing valve, each hydraulic control reversing valve and the bidirectional hydraulic lock, realizing the functions of front wheel steering, four-wheel steering and crab-shaped walking; The two two-position four-way electromagnetic reversing valves are a first electromagnetic reversing valve (31) and a second electromagnetic reversing valve (32); the first electromagnetic reversing valve (31) has two switching positions, one electromagnet D2 and four oil ports, namely oil port A, oil port B, oil port P and oil port T; the electromagnet D2 is arranged at the right end of the valve body of the first electromagnetic reversing valve (31); the oil port P and the oil port T of the first electromagnetic reversing valve (31) are respectively connected to and communicated with the P2 port and the T2 port of the mode switching valve group (3); the oil port A and the oil port B of the first electromagnetic reversing valve (31) are both connected to and communicated with the oil tank (5); the second electromagnetic reversing valve (32) has two switching positions, one electromagnet D1 and four oil ports, namely oil port A, oil port B, oil port P and oil port T; the electromagnet D1 is arranged at the right end of the valve body of the second electromagnetic reversing valve (32); the oil port P and the oil port T of the second electromagnetic reversing valve (32) are respectively connected to and communicated with the P1 port and the T1 port of the mode switching valve group (3); The three-position four-way electromagnetic reversing valve is a third electromagnetic reversing valve (33), which has three switching positions, two electromagnets D3 and D4, and four oil ports, namely oil port A, oil port B, oil port P and oil port T; the electromagnet D3 is arranged at the left end of the valve body of the third electromagnetic reversing valve (33), and the electromagnet D4 is arranged at the right end of the valve body of the third electromagnetic reversing valve (33); the oil port A and the oil port B of the third electromagnetic reversing valve (33) are respectively connected to and communicated with the A1 port and the B1 port of the mode switching valve group (3) through the bidirectional hydraulic lock (34); The four two-position three-way hydraulic control reversing valves are a first hydraulic control reversing valve (35), a second hydraulic control reversing valve (36), a third hydraulic control reversing valve (37) and a fourth hydraulic control reversing valve (38), which all have two switching positions and four oil ports, namely oil port P, oil port A, oil port B and control oil port K; The oil port P of the first hydraulic control reversing valve (35) is connected with the oil port A of the second electromagnetic reversing valve (32), the oil port A of the first hydraulic control reversing valve (35) is connected with the oil port T of the first electromagnetic reversing valve (31) and the T2 port of the mode switching valve group (3), the oil port B of the first hydraulic control reversing valve (35) is connected with the oil port B of the second hydraulic control reversing valve (36), and the control oil port K of the first hydraulic control reversing valve (35) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The oil port A of the second hydraulic control reversing valve (36) is connected with the oil port P of the first electromagnetic reversing valve (31), the oil port P of the second hydraulic control reversing valve (36) is connected with the oil port P of the third electromagnetic reversing valve (33), and the control oil port K of the second hydraulic control reversing valve (36) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The oil port P of the third hydraulic control reversing valve (37) is connected with the oil port T of the third electromagnetic reversing valve (33), the oil port B of the third hydraulic control reversing valve (37) is connected with the T2 port of the mode switching valve group (3), the oil port A of the third hydraulic control reversing valve (37) is connected with the oil port A of the fourth hydraulic control reversing valve (38), and the control oil port K of the third hydraulic control reversing valve (37) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The oil port P of the fourth hydraulic control reversing valve (38) is connected with the oil port B of the second electromagnetic reversing valve (32), the oil port B of the fourth hydraulic control reversing valve (38) is connected with the oil port P of the first electromagnetic reversing valve (31), and the control oil port K of the fourth hydraulic control reversing valve (38) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence.

2. The forklift truck steering control system according to claim 1, wherein: The steering gear (4) is provided with a steering oil circuit, the right turning oil port (41) of which is connected with the P1 port of the mode switching valve group (3) in communication, and the left turning oil port (42) is connected with the T1 port of the mode switching valve group (3) in communication.

3. The forklift truck steering control system according to claim 2, wherein: The system controller is provided with "front wheel steering", "four-wheel steering" and "crab walking" three steering mode gear switches, and is electrically connected with the first electromagnetic reversing valve (31), the second electromagnetic reversing valve (32) and the third electromagnetic reversing valve (33).

4. The forklift truck steering control system of claim 1 wherein: The front steering oil cylinder (10) and the rear steering oil cylinder (20) are both double-acting double-piston rod oil cylinders, and the cylinder diameter, rod diameter and stroke of the two are completely the same.

5. The forklift truck steering control system of claim 1 wherein: The front axle steering mechanism (1) further comprises two front wheels (11), and the two front wheels (11) are respectively hinged with both ends of the front steering oil cylinder (10) through steering arms.

6. The forklift truck steering control system of claim 1 wherein: The rear axle steering mechanism (2) further comprises two rear wheels (21), and the two rear wheels (21) are respectively hinged with both ends of the rear steering oil cylinder (20) through steering arms. The oil port P of the first hydraulic control reversing valve (35) is connected with the oil port A of the second electromagnetic reversing valve (32), the oil port A of the first hydraulic control reversing valve (35) is connected with the oil port T of the first electromagnetic reversing valve (31) and the T2 port of the mode switching valve group (3), the oil port B of the first hydraulic control reversing valve (35) is connected with the oil port B of the second hydraulic control reversing valve (36), and the control oil port K of the first hydraulic control reversing valve (35) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The oil port A of the second hydraulic control reversing valve (36) is connected with the oil port P of the first electromagnetic reversing valve (31), the oil port P of the second hydraulic control reversing valve (36) is connected with the oil port P of the third electromagnetic reversing valve (33), and the control oil port K of the second hydraulic control reversing valve (36) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The oil port P of the third hydraulic control reversing valve (37) is connected with the oil port T of the third electromagnetic reversing valve (33), the oil port B of the third hydraulic control reversing valve (37) is connected with the T2 port of the mode switching valve group (3), the oil port A of the third hydraulic control reversing valve (37) is connected with the oil port A of the fourth hydraulic control reversing valve (38), and the control oil port K of the third hydraulic control reversing valve (37) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The oil port P of the fourth hydraulic control reversing valve (38) is connected with the oil port B of the second electromagnetic reversing valve (32), the oil port B of the fourth hydraulic control reversing valve (38) is connected with the oil port P of the first electromagnetic reversing valve (31), and the control oil port K of the fourth hydraulic control reversing valve (38) is connected with the oil port B of the second electromagnetic reversing valve (32) in correspondence. The steering gear (4) is provided with a steering oil circuit, the right turning oil port (41) of which is connected with the P1 port of the mode switching valve group (3) in communication, and the left turning oil port (42) is connected with the T1 port of the mode switching valve group (3) in communication. The system controller is provided with "front wheel steering", "four-wheel steering" and "crab walking" three steering mode gear switches, and is electrically connected with the first electromagnetic reversing valve (31), the second electromagnetic reversing valve (32) and the third electromagnetic reversing valve (33). The front steering oil cylinder (10) and the rear steering oil cylinder (20) are both double-acting double-piston rod oil cylinders, and the cylinder diameter, rod diameter and stroke of the two are completely the same. The front axle steering mechanism (1) further comprises two front wheels (11), and the two front wheels (11) are respectively hinged with both ends of the front steering oil cylinder (10) through steering arms. The rear axle steering mechanism (2) further comprises two rear wheels (21), and the two rear wheels (21) are respectively hinged with both ends of the rear steering oil cylinder (20) through steering arms.

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