Steering hydraulic system and forklift

Abstract

The invention belongs to the field of industrial vehicles and discloses a steering hydraulic system and a forklift. The steering hydraulic system comprises a steering oil cylinder and a steering gear; the pressure cylinder comprises a small piston cylinder and a large piston cylinder which are located at the two ends, the large piston cylinder is hydraulically connected with an oil outlet of the steering gear, and the small piston cylinder is hydraulically connected with an oil cylinder cavity of the steering oil cylinder; the piston assembly of the pressure cylinder comprises a piston communication oil duct used for communicating cylinder cavities at the two ends of the pressure cylinder, and an oil duct on-off valve is arranged in the piston communication oil duct. The pressure output of the hydraulic system is improved by arranging the pressure cylinder, so that the difficulty of steering operation is reduced, steering is more convenient and flexible, the performance of steering operation is improved, and the response speed and stability of the system are also improved. The piston assembly of the pressure cylinder comprises a piston communicating oil duct used for communicating cylinder cavities at the two ends of the pressure cylinder, so that steering is sufficient, and the steering operation is not blocked.

Description

Technical Field

[0001] The present application belongs to the field of industrial vehicles, and in particular, relates to a forklift and a steering hydraulic system thereof. Background Art

[0002] A forklift is an industrial transport vehicle primarily used for loading, unloading, stacking, and short-distance transport of goods. It is widely used in warehouses, ports, factories, and other locations. In typical forklifts, the front forks extend to carry loads. After loading, these vehicles often require flexible steering during travel or transfers. However, under conditions such as idling, high internal leakage, and high steering speeds, heavy steering is very common, making operation laborious for the driver, resulting in a poor driving experience and low safety. This is especially true for forklifts with rear-mounted steering axles, where the steering pressure required for rear-mounted steering is even greater, and in some emergency situations, steering may even be impossible. Summary of the Invention

[0003] The object of the present application is to provide a steering hydraulic system and a forklift to improve the flexibility of steering operation.

[0004] To achieve the above objectives, the present application provides a steering hydraulic system, which includes: Steering cylinder and steering gear; The booster cylinder comprises a small piston cylinder and a large piston cylinder located at both ends, the large piston cylinder being hydraulically connected to the oil outlet of the steering gear, and the small piston cylinder being hydraulically connected to the cylinder cavity of the steering oil cylinder; Wherein, the piston assembly of the boosting cylinder includes a piston communicating oil passage for communicating the cylinder chambers at both ends of the boosting cylinder, and an oil passage on-off valve is provided in the piston communicating oil passage.

[0005] In some embodiments, the oil passage on-off valve is a one-way stop valve, which is configured to allow hydraulic oil to flow from the large piston cylinder of the booster cylinder to the small piston cylinder and to stop the flow in the opposite direction.

[0006] In some embodiments, the one-way stop valve is an adjustable one-way valve.

[0007] In some embodiments, the oil channel on-off valve is an electromagnetic switch valve.

[0008] In some embodiments, the steering hydraulic system further comprises: The piston travel switch comprises a first piston travel switch provided in the small piston cylinder and a second piston travel switch provided in the cylinder cavity of the steering cylinder; The controller is configured as: Determining that the first piston travel switch is triggered; Determining that the second piston travel switch is not triggered; The oil passage on-off valve is controlled to open to connect the piston to the oil passage.

[0009] In some embodiments, the piston assembly comprises: A small piston is located in the cylinder cavity of the small piston cylinder; A large piston is located in the cylinder cavity of the large piston cylinder; A piston linkage shaft rigidly connecting the small piston and the large piston; Wherein, the piston communicating oil passage is formed axially through the piston linkage shaft.

[0010] In some embodiments, the steering gear is provided with a first oil outlet and a second oil outlet, a first connecting oil circuit is provided between the first end of the steering cylinder and the first oil outlet, and a second connecting oil circuit is provided between the second end of the steering cylinder and the second oil outlet; The boosting cylinder includes a first boosting cylinder provided in the first connecting oil path and a second boosting cylinder provided in the second connecting oil path.

[0011] In some embodiments, the first boosting cylinder and the second boosting cylinder have the same structure and size.

[0012] In some embodiments, the steering hydraulic system further comprises: Hydraulic pumps; A priority valve is used to distribute the hydraulic oil pumped by the hydraulic pump to the steering gear having a manual pump function.

[0013] On the other hand, the present application further provides a forklift, comprising a rear-mounted steering axle and the above-mentioned steering hydraulic system, wherein the steering cylinder acts on the steering axle.

[0014] In the technical solution of the present application, a booster cylinder is added between the steering gear and the steering oil cylinder. By providing the booster cylinder, the pressure output of the hydraulic system is increased to achieve a booster drive effect, thereby reducing the difficulty of the steering operation and making the steering easier and more flexible. Among them, the piston assembly of the booster cylinder includes a piston connecting oil channel for connecting the cylinder chambers at both ends of the booster cylinder, so that the hydraulic oil output from the oil outlet of the steering gear can flow to the oil cylinder chamber of the steering oil cylinder through the large piston cylinder, the oil channel on-off valve, and the small piston cylinder in sequence, thereby pushing the piston of the steering oil cylinder to move to the bottom, so that the steering operation is not stuck and the steering is sufficient. After adding the booster cylinder, while effectively improving the performance of the steering operation, it also improves the response speed and stability of the system and optimizes the energy utilization efficiency of the hydraulic system.

[0015] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide a further understanding of the embodiments of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the embodiments of the present application, but do not constitute a limitation on the embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without inventive work. In the drawings: Figure 1 A partial hydraulic principle diagram of a steering hydraulic system according to a first embodiment of the present application; Figure 2 for Figure 1 A schematic diagram of the structure of the booster cylinder used in the embodiment of the present invention; Figure 3 is a complete hydraulic principle diagram of a steering hydraulic system according to a first embodiment of the present application; Figure 4 A partial hydraulic principle diagram of a steering hydraulic system according to a second embodiment of the present application; Figure 5 for Figure 4 Schematic diagram of the structure of the booster cylinder used in.

[0017] Description of Reference Numerals DETAILED DESCRIPTION

[0018] The following describes the specific embodiments of the present application in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not intended to limit the present application.

[0019] A forklift and a steering hydraulic system thereof according to the present application will be described below with reference to the accompanying drawings.

[0020] In common forklifts, the steering hydraulic system generally includes a hydraulic pump, a priority valve, a steering gear, a steering cylinder, etc. The hydraulic pump serves as the power source to supply oil to the system, the priority valve is used to distribute the hydraulic oil, the steering gear serves as the core control component to play a control and metering role, and the steering cylinder serves as the actuator. The steering gear outlet is connected to the steering cylinder. When internal leakage, excessive steering speed, and other factors lead to insufficient hydraulic oil, heavy steering is likely to occur, making the driver's operation difficult and affecting the driving experience and safety. Moreover, in the forklift's steering hydraulic system, the fully hydraulic steering gear itself has the function of a manual pump. However, since the forklift's steering axle is generally rear-mounted, the steering pressure required for rear-mounted steering is high, which causes the full hydraulic steering gear to lose its function as a manual pump and cannot be steered in an emergency.

[0021] To this end, the present application discloses a novel steering hydraulic system. Figure 1 As shown, in this embodiment, the new steering hydraulic system includes: Steering cylinder 7 and steering gear 5; The booster cylinder includes a small piston cylinder and a large piston cylinder at both ends. The large piston cylinder is hydraulically connected to the oil outlet of the steering gear 5, and the small piston cylinder is hydraulically connected to the cylinder cavity of the steering cylinder 7; Among them, the piston assembly of the boosting cylinder includes a piston communicating oil channel for connecting the cylinder chambers at both ends of the boosting cylinder, and an oil channel on-off valve is provided in the piston communicating oil channel.

[0022] It can be seen that a booster cylinder is specially added to the steering hydraulic system of the present application. As shown in the figure, the large end of the booster cylinder (i.e., the large piston cylinder) is connected to the oil outlet of the steering gear 5, and the small end of the booster cylinder (i.e., the small piston cylinder) is connected to the cylinder chamber of the steering cylinder 7. By providing the booster cylinder, the pressure output of the hydraulic system can be increased. That is, when the output oil pressure of the oil outlet of the steering gear 5 is the same, the oil pressure output to the steering cylinder 7 through the booster cylinder is greatly increased, which has a stronger driving force on the piston of the steering cylinder 7, thereby significantly reducing the force of the steering operation and making the steering more convenient and flexible.

[0023] The higher terminal output pressure of a booster cylinder also helps improve the hydraulic system's responsiveness and stability, ensuring more precise and reliable steering operations under complex operating conditions. Furthermore, installing a booster cylinder can optimize the hydraulic system's energy efficiency, reduce unnecessary energy loss, extend system life, and lower maintenance costs.

[0024] Specifically, if Figure 1 As shown, the key to introducing booster cylinders is to install them in series between the outlet of the steering gear 5 and the steering cylinder 7, forming a nearly closed circuit. Hydraulic oil from the outlet of the steering gear 5 first drives the booster cylinders, which then drive the steering cylinder 7. This achieves twice the result with half the effort, allowing for smooth steering cylinder 7 even at low output pressure, thus resolving the issue of heavy steering.

[0025] In more detail, Figure 2 The booster cylinder shown generally includes small piston cylinders at both ends (i.e. Figure 2 The upper end of the booster cylinder) and the large piston cylinder (i.e. Figure 2The lower end of the booster cylinder), the large piston cylinder is hydraulically connected to the oil outlet of the steering gear 5, and the small piston cylinder is hydraulically connected to the steering cylinder 7. After such arrangement, since the cylinder thrust is equal to the oil pressure multiplied by the piston effective area, the small piston cylinder of the booster cylinder is connected to the steering cylinder 7, and thus the pressure of the small piston cylinder of the booster cylinder is the same as the pressure of the steering cylinder 7. Also, since the piston area of ​​the large piston cylinder of the booster cylinder is several times the piston area of ​​the small piston cylinder, the pressure of the large piston cylinder of the booster cylinder is several times the pressure of the steering cylinder, and the large piston cylinder of the booster cylinder is connected to the steering gear outlet, so the pressure output by the steering gear is also several times the pressure of the steering cylinder, thereby achieving the effect of power assistance and reducing the force of turning the steering wheel. In addition, the booster cylinder can also improve the response speed and stability of the system, and ensure the accuracy and reliability of steering under complex working conditions.

[0026] However, in practice, long-term use of oil cylinders inevitably leads to oil leakage, which can cause the strokes of the booster cylinder and the steering cylinder to be out of sync and mismatched. For example, during operation, the piston of the booster cylinder may have reached its end position, while the piston of the steering cylinder 7 has not yet reached its end position, resulting in incomplete steering action of the steering cylinder 7.

[0027] Therefore, in the steering hydraulic system of the present application, the piston assembly of the booster cylinder includes a piston connecting oil passage for connecting the cylinder chambers at both ends of the booster cylinder, and an oil passage on-off valve is also provided in the piston connecting oil passage. Thus, even if the piston of the booster cylinder has reached its extreme position while the piston of the steering cylinder 7 has not, the hydraulic oil output from the first oil outlet A or the second oil outlet B of the steering gear 5 can flow sequentially through the large piston cylinder, the piston connecting oil passage, and the small piston cylinder to the cylinder chamber of the steering cylinder 7, thereby continuing to push the piston of the steering cylinder 7 to move, ensuring smooth steering operation without any stagnation.

[0028] The piston oil passage cannot be in a normally open state, otherwise the hydraulic oil in the large piston cylinder will directly reach the small piston cylinder through the piston oil passage, making the booster cylinder unable to boost pressure. To this end, an oil passage on-off valve is also set in the piston oil passage to control the opening and closing of the piston oil passage in time according to the stroke requirements.

[0029] In this embodiment, see Figure 2As an example, the oil passage on-off valve is a one-way stop valve 8, which is configured to allow hydraulic oil to flow from the large piston cylinder of the booster cylinder to the small piston cylinder and to cut off the flow in the opposite direction. Since the one-way stop valve 8 has a certain back pressure, such as the elastic pressure brought by the compression spring that elastically presses the valve core against the one-way valve port, the back pressure can, under normal circumstances, resist the hydraulic oil in the large piston cylinder and open the one-way stop valve 8 in the positive direction. When the piston stroke of the booster cylinder reaches the end extreme position, the hydraulic oil in the large piston cylinder continues to accumulate and the pressure increases, thereby resisting the compression spring and opening the one-way stop valve 8 in the positive direction, thereby opening the piston connecting oil passage, so that the hydraulic oil can flow through the large piston cylinder, the piston connecting oil passage, and the small piston cylinder in sequence to the cylinder chamber of the steering cylinder 7, thereby continuing to push the piston of the steering cylinder 7 to move.

[0030] It can be seen that when using a one-way stop valve 8, the back pressure setting, that is, the specification of the compression spring, is very important and needs to be appropriately selected based on the specifications of the booster cylinder and steering cylinder 7. Therefore, the one-way stop valve 8 is also the result of using an adjustable one-way valve, that is, the back pressure of the one-way valve is adjustable. As those skilled in the art will know, one-way valves with adjustable back pressure are common in the market and will not be elaborated on here.

[0031] In addition, the oil channel on-off valve can have various structures and control forms. For example, the oil channel on-off valve can be a hydraulic control valve or an electromagnetic control valve. For example, Figure 4 、 Figure 5 In the embodiment, the oil passage on-off valve adopts an electromagnetic switch valve 10. On this basis, the steering hydraulic system of this embodiment may further include: The piston travel switch includes a first piston travel switch 11 provided in the small piston cylinder and a second piston travel switch 12 provided in the cylinder cavity of the steering cylinder 7; The controller is configured as: Determine that the first piston travel switch 11 is triggered; Determine that the second piston travel switch 12 is not triggered; Control the opening of the oil passage on-off valve to open the piston and connect the oil passage.

[0032] Among them, travel switches can be set at the stroke ends of the small piston cylinder of the booster cylinder and the piston stroke ends of the steering cylinder 7 respectively. When the piston of the booster cylinder reaches the bottom and the piston of the steering cylinder has not reached the bottom, the electromagnetic switch valve 10 can be controlled to open, and the piston connecting oil channel can be opened, so that the hydraulic oil flows to the steering cylinder 7 through the piston connecting oil channel, and continues to push the steering cylinder 7 to work.

[0033] In this embodiment, a travel switch is used to help the controller determine the piston position, but it is obvious that the present application is not limited thereto. The piston position can be determined by various other methods, such as laser ranging, rope pulling, etc., which will not be elaborated here. In addition, the number of travel switches and their setting methods are not limited to Figure 4 、 Figure 5 shown.

[0034] exist Figure 5 In the booster cylinder, the piston assembly may include: A small piston is located in the cylinder cavity of the small piston cylinder; A large piston is located in the cylinder cavity of the large piston cylinder; The piston linkage shaft 6 rigidly connects the small piston and the large piston; The piston communicating oil passage is formed axially through the piston linkage shaft 6 .

[0035] Figure 2 、 Figure 5 This is a typical booster cylinder structure. Hydraulic oil from the oil outlet of the steering gear 5 first enters the cylinder cavity of the large piston cylinder. The hydraulic oil in the large piston cylinder pushes the large piston to move, which in turn drives the small piston to move synchronously through the piston linkage shaft 6. The piston linkage shaft 6 is a hollow shaft, and the two ends of the hollow shaft cavity connect the small piston cylinder and the large piston cylinder. In this way, the hollow shaft cavity forms a piston connecting oil channel, connecting the large and small piston cylinders. Furthermore, the hollow shaft cavity of the piston linkage shaft 6 can be equipped with an oil channel on-off valve, namely a one-way stop valve 8 or an electromagnetic switch valve 10.

[0036] Since an oil channel on-off valve is added to the piston of the booster cylinder, when the piston of the booster cylinder reaches the limit position but the piston of the steering cylinder has not reached the limit position, the oil channel on-off valve will be opened, connecting the small piston cylinder and the large piston cylinder to achieve compensation.

[0037] Figure 2 、 Figure 5 Both depict booster cylinders with oil passage shutoff valves, with the piston-connecting oil passages disposed within the piston linkage shaft 6. Alternatively, the piston-connecting oil passages are not limited to being disposed within the piston linkage shaft 6. For example, the piston-connecting oil passages may be separate hydraulic pipes connecting the large and small pistons. In this alternative, a piston-connecting oil passage, such as a hydraulic oil pipe, is also disposed between the small and large piston cylinders. This pipe may include a one-way shutoff valve 8, for example. The one-way shutoff valve 8 is configured to allow hydraulic oil to flow from the large piston cylinder to the small piston, but not in the reverse direction.

[0038] Since the large and small pistons are rigidly connected by a linkage shaft, that is, the piston assembly is an integrated moving part, when the steering oil pressure required by the cylinder chamber of the steering cylinder 7 is determined, the hydraulic oil pressure required by the cylinder chamber of the large piston cylinder is relatively small, that is, the outlet oil pressure of the steering gear 5 can be relatively small. As mentioned above, the ratio between the steering oil pressure required by the steering cylinder 7 and the outlet oil pressure of the steering gear 5 should be the ratio of the piston areas of the large and small pistons. Therefore, the larger the piston area ratio between the large piston and the small piston, the more obvious the boost effect. As an example, Figure 1 、 Figure 2 In the boost cylinder shown, the piston area ratio between the large and small pistons should be no less than 2. Of course, the present application is not limited thereto, and the piston area ratio can be set larger or smaller, which can be specifically determined and selected according to specific working conditions.

[0039] The piston assembly of the booster cylinder of this application is not limited to Figure 2 The structural form of the large and small pistons and the piston linkage shaft 6 shown, optionally, the large and small pistons can also be an integrated structure, that is, the piston assembly is a stepped shaft, the small shaft end of the stepped shaft serves as the small piston, and the large shaft end serves as the large piston, which is convenient for integrated processing and molding.

[0040] It should be noted that, in the steering hydraulic system of this embodiment, only one booster cylinder may be provided according to the working conditions, that is, only one side of the steering operation is assisted. Figure 1 、 Figure 4 As shown, there are generally two boosting cylinders, namely the first boosting cylinder 61 and the second boosting cylinder 62. Figure 3 The steering gear 5 is provided with a first oil outlet A and a second oil outlet B, a first connecting oil circuit is provided between the first end of the steering cylinder 7 and the first oil outlet A, and a second connecting oil circuit is provided between the second end and the second oil outlet B; the booster cylinder includes a first booster cylinder 61 provided in the first connecting oil circuit and a second booster cylinder 62 provided in the second connecting oil circuit.

[0041] Due to the balance and symmetry of left and right steering operations, the first booster cylinder 61 and the second booster cylinder 62 can be of the same specifications, that is, the same structure and size. Of course, depending on the required amount of power assistance, the first and second booster cylinders can also be of different specifications and sizes. In this case, the hydraulic system design must pay attention to the overflow and replenishment requirements.

[0042] See also Figure 3 The steering hydraulic system of this embodiment includes not only the steering gear 5, the steering cylinder 7 and the booster cylinder, but also includes: Hydraulic pump 2; The priority valve 4 is used to distribute the hydraulic oil pumped by the hydraulic pump 2 to the steering gear 5 with a manual pump function.

[0043] Among them, the hydraulic pump 2 supplies oil to the system, the priority valve 4 is used to distribute the pumped hydraulic oil, the steering gear 5 is the core control component, which plays the role of control and metering, the steering cylinder 7 is the steering execution component, and the outlet of the steering gear 5 is connected to the steering cylinder 7. Figure 5 In the embodiment, the priority valve 4 and the steering gear 5 are all known valves commonly found in the market, and thus are not described in detail here. As can be seen from the figure, the steering gear 5 has a manual pump function.

[0044] visible, Figure 3 An improved power steering system is disclosed in the embodiment, which consists of a filter 1, a hydraulic pump 2, a pump oil one-way valve 3, a priority valve 4, a steering gear 5, a booster cylinder, and a steering oil cylinder 7. The hydraulic oil pumped by the hydraulic pump 2 first passes through the priority valve 4 for flow distribution, enters the P port of the steering gear 5, and is connected to the large piston chamber of the booster cylinder from the outlet of the steering gear 5 after being metered by the steering gear 5. The large piston and the small piston of the booster cylinder are hard-connected, and the areas of the large piston cylinder and the small piston cylinder are proportional. The small piston cylinder is connected to the steering oil cylinder 7. Among them, a connecting oil channel with a one-way stop valve 8 is added between the large piston cylinder and the small piston cylinder of the booster cylinder to supplement the oil leakage during the working process.

[0045] In addition, the present application also protects a forklift, comprising a rear-mounted steering axle (not shown) and the above-mentioned steering hydraulic system, wherein the steering cylinder 7 acts on the steering axle.

[0046] Since the steering axle of a forklift is generally rear-mounted, the steering pressure requirement is large. When the system has no power, for example, when the hydraulic oil is pumped and distributed to other work accessories through the priority valve, the full hydraulic steering gear will lose its function as a manual pump, and steering will be impossible in an emergency. At this time, after adopting the steering hydraulic system of the present application, even if the pressure of the hydraulic oil passing through the steering gear 5 is low, a larger pressure output can be obtained, and the pressure output by the steering gear can be proportionally reduced. The area of ​​the large piston cylinder of the booster cylinder is proportional to the area of ​​the small piston cylinder. According to F=PA, the pressure of the large piston cylinder is less than that of the small piston cylinder. The small piston cylinder is connected to the steering oil cylinder 7, and the large piston cylinder is connected to the outlet of the steering gear 5. Therefore, the force of turning the steering wheel can be reduced and the service life of the steering gear 5 can be extended.

[0047] The steering hydraulic system of the present application can also improve the accuracy of the system. Since the diameter of the large piston cylinder of the booster cylinder is proportional to the diameter of the small piston cylinder, the flow input of the large piston cylinder will be proportionally amplified, thereby improving the accuracy of steering. Moreover, it can also realize the function of a manual pump for the steering gear, which can steer in an emergency and improve safety. The booster cylinder can make the outlet pressure of the steering gear very small, so that the force acting on the steering gear rotor is small, thereby achieving unpowered manual steering. On this basis, the problem that large-tonnage forklifts cannot directly use the steering gear due to excessive pressure can be solved.

[0048] In the description of this application, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0049] In this application, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection, or communication; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0050] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

Claims

1. A steering hydraulic system, characterized in that: The steering hydraulic system comprises: Steering cylinder (7) and steering gear (5); A booster cylinder comprising a small piston cylinder and a large piston cylinder at both ends, wherein the large piston cylinder is hydraulically connected to the oil outlet of the steering gear (5), and the small piston cylinder is hydraulically connected to the oil cylinder chamber of the steering oil cylinder (7); Wherein, the piston assembly of the boosting cylinder includes a piston communicating oil passage for communicating the cylinder chambers at both ends of the boosting cylinder, and an oil passage on-off valve is provided in the piston communicating oil passage.

2. The steering hydraulic system according to claim 1, characterized in that: The oil passage on-off valve is a one-way stop valve (8), and the one-way stop valve (8) is configured to allow hydraulic oil to flow from the large piston cylinder of the booster cylinder to the small piston cylinder and to stop the flow in the opposite direction.

3. The steering hydraulic system according to claim 2, characterized in that: The one-way stop valve (8) is an adjustable one-way valve.

4. The steering hydraulic system according to claim 1, characterized in that: The oil channel on-off valve is an electromagnetic switch valve (10).

5. The steering hydraulic system according to claim 4, characterized in that: The steering hydraulic system also includes: A piston travel switch, comprising a first piston travel switch (11) arranged in the small piston cylinder and a second piston travel switch (12) arranged in the cylinder cavity of the steering cylinder (7); The controller is configured as: Determining that the first piston travel switch (11) is triggered; Determining that the second piston travel switch (12) is not triggered; The oil passage on-off valve is controlled to open to connect the piston to the oil passage.

6. The steering hydraulic system according to claim 1, characterized in that: The piston assembly comprises: A small piston is located in the cylinder cavity of the small piston cylinder; A large piston is located in the cylinder cavity of the large piston cylinder; A piston linkage shaft (6) rigidly connecting the small piston and the large piston; The piston communicating oil passage is formed axially through the piston linkage shaft (6).

7. The steering hydraulic system according to any one of claims 1 to 6, characterized in that: The steering gear (5) is provided with a first oil outlet (A) and a second oil outlet (B); a first connecting oil circuit is provided between the first end of the steering cylinder (7) and the first oil outlet (A), and a second connecting oil circuit is provided between the second end and the second oil outlet (B); The boosting cylinder comprises a first boosting cylinder (61) arranged in the first connecting oil circuit and a second boosting cylinder (62) arranged in the second connecting oil circuit.

8. The steering hydraulic system according to claim 7, characterized in that: The first boosting cylinder (61) and the second boosting cylinder (62) have the same structure and size.

9. The steering hydraulic system according to claim 1, characterized in that: The steering hydraulic system also includes: Hydraulic pump (2); A priority valve (4) is used to distribute the hydraulic oil pumped by the hydraulic pump (2) to the steering gear (5) having a manual pump function.

10. A forklift, characterized in that: The forklift comprises a rear-mounted steering axle and a steering hydraulic system according to any one of claims 1 to 9, wherein the steering cylinder (7) acts on the steering axle.

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