Steering hydraulic system and fork lift truck

Abstract

This application pertains to the field of industrial vehicles and discloses a steering hydraulic system and a forklift. The steering hydraulic system includes a steering gear with first and second oil outlets; a steering cylinder with a first connecting oil passage between its first end and the first oil outlet, and a second connecting oil passage between its second end and the second oil outlet; and a booster cylinder, including a first booster cylinder disposed in the first connecting oil passage and a second booster cylinder disposed in the second connecting oil passage. Both the first and second booster cylinders include a small piston cylinder and a large piston cylinder located at both ends. The large piston cylinder is hydraulically connected to the oil outlet of the steering gear, and the small piston cylinder is hydraulically connected to the cylinder chamber of the steering cylinder; and a replenishing valve, which is a replenishing and balancing oil passage disposed between the small piston cylinders of the first and second booster cylinders. By adding a booster cylinder, this application achieves a boosted drive effect, making steering lighter and more flexible. Furthermore, by setting up a replenishing valve, it can be used to achieve oil balance between the two cylinders in a timely manner.

Description

Technical Field

[0001] This application belongs to the field of industrial vehicles, and specifically relates to a forklift and its steering hydraulic system. Background Technology

[0002] Forklifts are frequently used in industrial sites such as warehouses, ports, and factories for loading, unloading, stacking, and short-distance transport of goods. When a forklift is operating, the front end is heavily loaded, requiring timely and flexible steering. However, under certain conditions, such as idling, high internal leakage, or high steering speeds, heavy steering can easily occur, making it difficult for the driver to operate and affecting the driving experience and safety. Furthermore, while the fully hydraulic steering system of a forklift inherently possesses a manual pump function, the rear-mounted steering axle of a forklift typically requires high steering pressure, causing the fully hydraulic steering system to lose its manual pump function, rendering it unable to steer in emergency situations. Utility Model Content

[0003] The purpose of this application is to provide a steering hydraulic system and a forklift to optimize and improve the operational performance of the steering hydraulic system.

[0004] To achieve the above objectives, this application provides a steering hydraulic system, the steering hydraulic system comprising:

[0005] The steering gear is equipped with a first oil outlet and a second oil outlet;

[0006] A steering cylinder, wherein a first connecting oil passage is provided between a first end of the steering cylinder and a first oil outlet, and a second connecting oil passage is provided between a second end of the steering cylinder and a second oil outlet; and

[0007] The booster cylinder includes a first booster cylinder disposed in the first connecting oil circuit and a second booster cylinder disposed in the second connecting oil circuit. Both the first booster cylinder and the second booster cylinder include a small piston cylinder and a large piston cylinder located at both ends. The piston area ratio between the large piston cylinder and the small piston cylinder is not less than 2. The large piston cylinder is hydraulically connected to the oil outlet of the steering gear, and the small piston cylinder is hydraulically connected to the oil cylinder chamber of the steering cylinder.

[0008] The oil replenishment valve is installed in the oil replenishment and balance circuit between the small piston cylinder of the first booster cylinder and the small piston cylinder of the second booster cylinder.

[0009] In some embodiments, the replenishing valve is a solenoid directional valve.

[0010] In some embodiments, the steering hydraulic system further includes:

[0011] The pressure sensor includes a first pressure sensor disposed in the small piston cylinder of the first booster cylinder and a second pressure sensor disposed in the small piston cylinder of the second booster cylinder;

[0012] The controller is configured as follows:

[0013] The detected pressure difference between the first pressure sensor and the second pressure sensor is determined to be greater than a preset pressure difference value;

[0014] Control the replenishing valve to open the replenishing and balancing oil circuit.

[0015] In some embodiments, the replenishing valve is a three-position four-way directional valve with an O-type neutral position function.

[0016] In some embodiments, the piston assembly of the booster cylinder includes a small piston in the small piston cylinder, a large piston in the large piston cylinder, and a piston connecting oil passage for connecting the two cylinder chambers, wherein an oil passage on / off valve is provided in the piston connecting oil passage.

[0017] In some embodiments, the piston assembly includes a piston linkage shaft that rigidly connects the small piston and the large piston. The piston linkage shaft is a hollow shaft, and a one-way shut-off valve serving as the oil passage on / off valve is provided in the hollow shaft cavity. The one-way shut-off valve is configured to allow hydraulic oil to flow from the large piston cylinder to the small piston cylinder and to shut off in the reverse direction.

[0018] In some embodiments, the oil passage on / off valve is an electromagnetic switch valve.

[0019] In some embodiments, the steering hydraulic system further includes:

[0020] The piston stroke switch includes a first piston stroke switch disposed in the small piston cylinder and a second piston stroke switch disposed in the cylinder chamber of the steering cylinder.

[0021] The controller is configured as follows:

[0022] It is confirmed that the first piston limit switch has been triggered;

[0023] It was determined that the second piston limit switch was not triggered;

[0024] The control opens the oil passage on / off valve to connect the piston to the oil passage.

[0025] In some embodiments, the piston assembly is a stepped shaft with an integral structure.

[0026] In some embodiments, the steering hydraulic system further includes:

[0027] Hydraulic pump;

[0028] A priority valve is used to distribute the pumped hydraulic oil from the hydraulic pump to the steering gear, which has a manual pump function.

[0029] This application also provides a forklift, including a rear-mounted steering axle and the aforementioned steering hydraulic system, wherein the steering cylinder acts on the steering axle.

[0030] In the technical solution of this application, booster cylinders are added to the two connecting oil circuits between the steering gear and the steering cylinder, namely, a first booster cylinder and a second booster cylinder. This allows the hydraulic oil with low pressure to drive the booster cylinders and push the steering cylinder, achieving a boosted drive effect and increasing the pressure output of the hydraulic system. This significantly reduces the steering effort, making steering lighter and more agile. Furthermore, by setting a replenishing valve in the oil replenishment and balancing oil circuit between the small piston cylinders of the first and second booster cylinders, oil balance between the two cylinders can be achieved in a timely manner. Therefore, while effectively improving steering performance, it also enhances the system's response speed and stability, and optimizes the energy utilization efficiency of the hydraulic system.

[0031] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the embodiments of this application and form part of the specification. They are used together with the following detailed description to explain the embodiments of this application, but do not constitute a limitation on the embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without any inventive effort. In the drawings:

[0033] Figure 1 This is a partial hydraulic schematic diagram of a steering hydraulic system according to the first embodiment of this application;

[0034] Figure 2 for Figure 1 Hydraulic schematic diagram of the replenishing valve used in the process;

[0035] Figure 3 for Figure 1 A schematic diagram of the booster cylinder used in the process;

[0036] Figure 4 A complete hydraulic schematic diagram of the steering hydraulic system according to the first embodiment of this application;

[0037] Figure 5 This is a partial hydraulic schematic diagram of the steering hydraulic system according to the second embodiment of this application;

[0038] Figure 6 for Figure 5A schematic diagram of the booster cylinder used in the process.

[0039] Explanation of reference numerals in the attached figures

[0040] Detailed Implementation

[0041] The specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0042] The forklift and its steering hydraulic system according to this application are described below with reference to the accompanying drawings.

[0043] This application discloses a novel hydraulic steering system. For example... Figure 1 As shown, in this embodiment, the steering hydraulic system includes:

[0044] Steering gear 5 is provided with a first oil outlet A and a second oil outlet B;

[0045] A steering cylinder 7 has a first connecting oil passage L1 between its first end and a first oil outlet A, and a second connecting oil passage L2 between its second end and a second oil outlet B; and

[0046] The booster cylinder includes a first booster cylinder 61 disposed in the first connecting oil circuit L1 and a second booster cylinder 62 disposed in the second connecting oil circuit L2. Both the first booster cylinder 61 and the second booster cylinder 62 include a small piston cylinder and a large piston cylinder located at both ends. The piston area ratio between the large piston cylinder and the small piston cylinder is not less than 2. 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 cylinder 7.

[0047] The oil replenishment valve 9 is located in the oil replenishment and balance oil circuit between the small piston cylinder of the first booster cylinder 61 and the small piston cylinder of the second booster cylinder 62.

[0048] This application firstly increases the pressure output of the hydraulic system by adding a booster cylinder, thereby significantly reducing the steering effort and making steering lighter and more agile. For example... Figure 1 As shown, the key to creatively introducing the booster cylinder lies in connecting two booster cylinders in series between the outlet of the steering gear 5 and the steering cylinder 7, forming an approximately closed loop. The hydraulic oil at the outlet of the steering gear 5 first drives the booster cylinder, and then drives the steering cylinder 7 through the booster cylinder, thus achieving twice the result with half the effort. It can smoothly drive the steering cylinder 7 even with low pressure output, solving the problem of heavy steering.

[0049] like Figure 3 As shown, a booster cylinder typically includes small piston cylinders located at both ends (i.e., Figure 3The upper end of the booster cylinder) and the large piston cylinder (i.e. Figure 3 The booster cylinder (located at its lower end) is hydraulically connected to the outlet of the steering gear 5 via a large piston cylinder, and to the steering cylinder 7 via a small piston cylinder. With this configuration, since the cylinder thrust equals the hydraulic pressure multiplied by the piston's working area, and the small piston cylinder of the booster cylinder is connected to the steering cylinder 7, the pressure of the small piston cylinder of the booster cylinder is the same as the pressure of the steering cylinder 7. Furthermore, because the piston area ratio between the large and small piston cylinders is not less than 2 (meaning the piston area of ​​the large piston cylinder of the booster cylinder is more than twice that of the small piston cylinder), the pressure of the large piston cylinder of the booster cylinder is a fraction of the pressure of the steering cylinder. Since the large piston cylinder of the booster cylinder is connected to the steering gear outlet, the pressure output by the steering gear is also a fraction of the pressure of the steering cylinder, thus achieving a power assist effect and reducing the force required to turn the steering wheel. In addition, the booster cylinder can improve the system's response speed and stability, ensuring steering accuracy and reliability under complex operating conditions.

[0050] like Figure 4 As shown, the steering hydraulic system of a forklift generally consists of a hydraulic pump 2, a priority valve 4, a steering gear 5, and a steering cylinder 7. The hydraulic pump 2 serves as the power source, supplying oil to the system; the priority valve 4 distributes the hydraulic oil; the steering gear 5, as the core control component, plays a role in control and metering; and the steering cylinder 7, as the actuator, is connected to the outlet of the steering gear 5. When internal leakage, excessive steering wheel turning speed, or other factors lead to insufficient hydraulic oil, heavy steering can easily occur, causing the driver to exert considerable effort and affecting driving experience and safety. By setting up a first booster cylinder 61 and a second booster cylinder 62, not only can the heavy steering problem be solved, but the system's response speed and stability can also be improved, ensuring steering accuracy and reliability under complex working conditions. Simultaneously, the energy utilization efficiency of the hydraulic system can be optimized, reducing unnecessary energy loss, extending system lifespan, and lowering maintenance costs, bringing multiple benefits to the steering system.

[0051] Secondly, in addition to adding a booster cylinder, this application also includes... Figure 2 The oil replenishing valve 9 shown is located in the oil replenishing and balancing oil circuit between the small piston cylinder of the first booster cylinder 61 and the small piston cylinder of the second booster cylinder 62. This oil replenishing and balancing oil circuit is used to hydraulically connect the first connecting oil circuit L1 and the second connecting oil circuit L2 on both sides. Figure 2 As shown. This is because in actual operation, there may be a difference in the hydraulic oil capacity of the first and second booster cylinders on both sides. By setting the oil replenishment valve 9, the on / off of the oil replenishment and balance circuit can be controlled to achieve oil balance between the two cylinders.

[0052] The oil replenishment and balancing circuit is used for hydraulic connection between the first and second booster cylinders, and the oil replenishment valve 9 serves as the oil circuit on / off control valve. (See also...) Figure 1 , Figure 2Its working principle is as follows: Hydraulic oil is supplied from the first outlet A of the steering gear 5 to the first booster cylinder 61. When the first booster cylinder 61 has not reached its limit position while the steering cylinder 7 has reached its limit position, the second booster cylinder 62 has also not reached its limit position, meaning that the hydraulic oil in the first booster cylinder 61 is more than that in the second booster cylinder 62. At this time, once it is detected that the pressure on the left side is greater than that on the right side, it can be controlled... Figure 2 When the solenoid 1YA of the replenishing valve 9 is energized, the replenishing and balancing oil circuit is opened through the replenishing valve 9, which connects the left and right booster cylinders. This causes excess hydraulic oil in the small piston cylinder of the first booster cylinder 61 to flow to the small piston cylinder of the second booster cylinder 62. Once the pressure on both sides is equal, the replenishing valve 9 is controlled to return to the neutral position, disconnecting the oil circuit. Conversely, when the right solenoid valve 2YA is energized, excess hydraulic oil in the second booster cylinder 62 flows to the first booster cylinder 61, thus equalizing the hydraulic oil levels in the left and right booster cylinders.

[0053] like Figure 2 As shown in the example, the replenishing valve 9 employs a three-position four-way directional valve with an O-type neutral position function. When the electromagnets at both ends are not energized, the three-position four-way replenishing valve 9 is in the neutral position, i.e., the shut-off position. The three ports of the replenishing valve 9 are mutually shut off when in the neutral position, thus cutting off the replenishing and balancing oil circuit. When any electromagnet is energized, the replenishing and balancing oil circuit will be opened, i.e., the first connecting oil circuit L1 and the second connecting oil circuit L2 on both sides are hydraulically connected.

[0054] Of course, those skilled in the art will understand that the replenishing valve 9 is not limited to the three-position four-way directional valve with O-type neutral position function described above, but may also be, for example, a two-position two-way switching valve, etc. The replenishing valve 9 is also not limited to a solenoid valve, but may also be a hydraulically controlled valve, etc., which will not be shown or described here.

[0055] In this embodiment, based on the use of a common solenoid directional valve for the replenishing valve 9, the steering hydraulic system may further include:

[0056] The pressure sensor includes a first pressure sensor (not shown) disposed in the small piston cylinder of the first booster cylinder 61 and a second pressure sensor (not shown) disposed in the small piston cylinder of the second booster cylinder 62.

[0057] The controller is configured as follows:

[0058] The detected pressure difference between the first pressure sensor and the second pressure sensor is determined to be greater than a preset pressure difference value;

[0059] Control the replenishing valve 9 to open the replenishing and balancing oil circuit.

[0060] As can be seen, the controller can determine whether there is a pressure imbalance between the two booster cylinders based on the oil pressure difference in the small piston cylinders, and then control the oil replenishment and balancing circuit to balance the pressure of the two booster cylinders. The preset pressure difference value can be specifically set according to different models and specifications of the booster cylinders. Alternatively, in other embodiments, a limit switch or similar device can be used instead of a pressure sensor to determine whether the two booster cylinders are out of sync or have a pressure imbalance.

[0061] It should be noted that in practical applications, hydraulic cylinders used for a long time will inevitably experience oil leakage, which will cause the strokes of the booster cylinder and the steering cylinder to be out of sync or mismatched. For example, during operation, the piston stroke of the booster cylinder may reach its extreme position, while the piston of the steering cylinder 7 may not have reached its extreme position, resulting in the steering action of the steering cylinder 7 being incomplete.

[0062] Therefore, in the steering hydraulic system of this embodiment, the piston assembly of the booster cylinder includes a small piston in a small piston cylinder, a large piston in a large piston cylinder, and a piston connecting oil passage for connecting the two cylinder chambers of the booster cylinder. An oil passage on / off valve is also provided in the piston connecting oil passage. Thus, even if the piston of the booster cylinder reaches its extreme position while the piston of the steering cylinder 7 does not, the hydraulic oil output from the first outlet A or the second 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 and full steering.

[0063] The piston connecting oil passage cannot be in a normally open state; otherwise, the hydraulic oil from the large piston cylinder will flow directly to the small piston cylinder through the piston connecting oil passage, preventing the booster cylinder from functioning as a booster. Therefore, an on / off valve is installed in the piston connecting oil passage to control its opening and closing as needed based on stroke requirements.

[0064] In this embodiment, see Figure 1 , Figure 3 As an example, the oil passage on / off valve is a one-way shut-off valve 8. The one-way shut-off 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 cut off the flow in the reverse direction. When the piston of the booster cylinder reaches its limit position while the steering cylinder has not reached its limit position, the one-way shut-off valve 8 will be opened in the forward direction by the hydraulic oil, thus playing a compensating role.

[0065] Because the one-way shut-off 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, this back pressure can normally resist the hydraulic oil of the large piston cylinder from opening the one-way shut-off valve 8 in the forward direction. When the piston stroke of the booster cylinder reaches the extreme position at the end, the hydraulic oil in the large piston cylinder continuously accumulates and the pressure increases, thereby resisting the compression spring and opening the one-way shut-off valve 8 in the forward direction. This opens the piston connecting oil passage, allowing the hydraulic oil to 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.

[0066] It is evident that when using the one-way shut-off valve 8, the setting of its back pressure, i.e., the selection of the compression spring specifications, is crucial and needs to be appropriately chosen based on the specifications of the booster cylinder and the steering cylinder 7. Therefore, the one-way shut-off valve 8 is also designed as an adjustable one-way valve, meaning the back pressure of the one-way valve is adjustable. Those skilled in the art will know that adjustable back pressure one-way valves are common in the market, and will not be elaborated upon further here.

[0067] Furthermore, oil passage on / off valves can have various structures and control methods. For example, an oil passage on / off valve can be a hydraulically controlled valve or a solenoidally controlled valve. Figure 5 , Figure 6 In this embodiment, the oil passage on / off valve is an electromagnetic switch valve 10. Based on this, the steering hydraulic system of this embodiment may further include:

[0068] The piston limit switch includes a first piston limit switch 11 disposed in the small piston cylinder and a second piston limit switch 12 disposed in the cylinder chamber of the steering cylinder 7.

[0069] The controller is configured as follows:

[0070] Confirm that the first piston limit switch 11 has been triggered;

[0071] It has been determined that the second piston limit switch 12 has not been triggered;

[0072] Control the opening of the oil passage on / off valve to allow the piston to connect to the oil passage.

[0073] In this design, limit switches can be installed at the end of the stroke of the small piston cylinder of the booster cylinder and at the end of the piston stroke of the steering cylinder 7. When the piston of the booster cylinder reaches the bottom, but the piston of the steering cylinder does not reach the bottom, the solenoid switch valve 10 can be opened to connect the piston to the oil passage, so that the hydraulic oil flows to the steering cylinder 7 through the piston to continue to drive the steering cylinder 7 to work.

[0074] In this embodiment, limit switches are used to help the controller determine the piston position. However, this application is obviously not limited to this. Various other methods can be used to determine the piston position, such as laser ranging, pull-string methods, etc., which will not be elaborated here. In addition, the number of limit switches and their arrangement are not limited to this. Figure 1 , Figure 3 , Figure 5 , Figure 6 As shown.

[0075] exist Figure 3 or Figure 6 The piston assembly of the aforementioned booster cylinder may include:

[0076] The small piston is located in the cylinder chamber of the small piston cylinder;

[0077] The large piston is located in the cylinder chamber of the large piston cylinder;

[0078] Piston linkage shaft 6, rigidly connecting the small piston and the large piston;

[0079] The piston connecting oil passage is formed axially through the piston linkage shaft 6.

[0080] Figure 3 , Figure 6 In a typical booster cylinder structure, the hydraulic oil from the outlet of the steering gear 5 first enters the cylinder chamber 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 via the piston linkage shaft 6. The piston linkage shaft 6 is a hollow shaft, with both ends of the hollow shaft cavity connecting the small piston cylinder and the large piston cylinder. Thus, the hollow shaft cavity forms a piston-connecting oil passage, connecting the large and small piston cylinders. Furthermore, the hollow shaft cavity of the piston linkage shaft 6 can be equipped with an oil passage on / off valve, such as a one-way shut-off valve 8 or a solenoid switch valve 10.

[0081] Because an oil passage on / off valve is added to the piston of the booster cylinder, when the piston of the booster cylinder reaches its limit position while the piston of the steering cylinder does not reach its limit position, the oil passage on / off valve will be opened, connecting the small piston cylinder and the large piston cylinder to achieve a compensation effect.

[0082] Figure 3 , Figure 6 Both examples show a booster cylinder with an on / off valve for the piston passage, where the piston-connecting oil passage is located in the piston linkage shaft 6. Alternatively, the piston-connecting oil passage is not limited to being located in the piston linkage shaft 6; for example, the piston-connecting oil passage could be a separate hydraulic pipe connecting the large and small pistons. In this alternative, a piston-connecting oil passage is also provided between the small and large piston cylinders, such as a hydraulic oil pipe, which may contain a one-way shut-off valve 8. The one-way shut-off valve 8 is configured to allow hydraulic oil to flow from the large piston cylinder to the small piston and to cut off the flow in the reverse direction.

[0083] Since the large and small pistons are rigidly connected by a linkage shaft, meaning the piston assembly is a single moving part, given a fixed steering oil pressure required for the cylinder chamber of steering cylinder 7, the hydraulic oil pressure required for the large piston cylinder is relatively small; that is, a relatively small outlet oil pressure from steering gear 5 is sufficient. As mentioned earlier, the ratio between the steering oil pressure required for steering cylinder 7 and the outlet oil pressure from 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 and small pistons, the more pronounced the booster effect. As an example, Figure 3 , Figure 6 In the booster cylinder shown, the piston area ratio between the large and small pistons should be no less than 2. However, this application is not limited to this; the piston area ratio can be determined and selected according to specific operating conditions.

[0084] The piston assembly of the booster cylinder in this application is not limited to... Figure 3 , Figure 6 The structure of the large and small pistons and piston linkage shaft 6 shown can be optionally integrated, with the piston assembly being a stepped shaft, the small end of the stepped shaft serving as the small piston, and the large end serving as the large piston, which facilitates integral machining.

[0085] See Figure 4 The steering hydraulic system of this embodiment includes not only the steering gear 5, the steering cylinder 7, and the booster cylinder, but may also include:

[0086] Hydraulic pump 2;

[0087] Priority valve 4 is used to distribute the pumped hydraulic oil from hydraulic pump 2 to steering gear 5, which has a manual pump function.

[0088] Hydraulic pump 2 supplies oil to the system, priority valve 4 distributes the pumped hydraulic oil, steering gear 5, as the core control component, plays a role in control and metering, and steering cylinder 7 is the steering actuator; the outlet of steering gear 5 is connected to steering cylinder 7. Figure 5 In this diagram, the priority valve 4 and the steering gear 5 both use commonly available valve components, so they will not be described in detail here. As can be seen from the diagram, the steering gear 5 has a manual pump function.

[0089] In conclusion, Figure 1 , Figure 5In this embodiment, an internally replenished power steering hydraulic system is disclosed, comprising a filter 1, a hydraulic pump 2, a pump oil check valve 3, a priority valve 4, a steering gear 5, a booster cylinder, and a steering cylinder 7. The hydraulic oil pumped by the hydraulic pump 2 first passes through the priority valve 4 for flow distribution, then enters the P port of the steering gear 5. After being metered by the steering gear 5, the oil exits from the steering gear 5 and connects to the large piston chamber of the booster cylinder. The large and small pistons of the booster cylinder are rigidly connected, with their areas proportional. The small piston cylinder is connected to the steering cylinder 7. Based on the addition of a booster pump, a replenishment valve 9 is installed, and its opening and closing can be controlled by detecting the pressure difference between the left and right booster cylinders. Furthermore, a piston-connecting oil passage with a control valve can be added between the large and small piston cylinders of the booster cylinder to compensate for oil leakage during operation.

[0090] In addition, this application also protects a forklift including a rear-mounted steering axle (not shown) and the aforementioned steering hydraulic system, wherein the steering cylinder 7 acts on the steering axle.

[0091] Since forklift steering axles are generally rear-mounted, the steering pressure requirement is high. When the system is without power, such as when pumping hydraulic oil to other work attachments via a priority valve, the fully hydraulic steering gear loses its function as a manual pump, making steering impossible in emergencies. In this situation, the steering hydraulic system of this application, even with low hydraulic oil pressure through the steering gear 5, can still achieve a large pressure output, proportionally reducing the output pressure of the steering gear. The areas of the large and small piston cylinders in the booster cylinder are proportional; according to F=PA, the pressure of the large piston cylinder is less than the pressure of the small piston cylinder. The small piston cylinder is connected to the steering cylinder 7, and the large piston cylinder is connected to the outlet of the steering gear 5. Therefore, it reduces the effort required to turn the steering wheel and extends the service life of the steering gear 5.

[0092] The steering hydraulic system described in this application also improves system accuracy. Because the diameters of the large and small piston cylinders in the booster cylinder are proportional, the flow input to the large piston cylinder is proportionally amplified, thus improving steering precision. Furthermore, it enables the steering gear to function as a manual pump, allowing for steering in emergencies and improving safety. The booster cylinder reduces the steering gear outlet pressure, resulting in a smaller force acting on the steering gear rotor, thereby enabling manual steering without power. Based on this, it solves the problem of large-tonnage forklifts being unable to directly use the steering gear due to excessively high pressure.

[0093] In actual operation, in the case of different hydraulic oil capacities between the first and second booster cylinders on both sides, the oil replenishment valve 9 can be set to control the opening and closing of the oil replenishment and balance circuit, so as to achieve oil balance between the two cylinders.

[0094] This application also adds a piston connecting oil passage and its oil passage on / off valve to the piston assembly of the booster cylinder. When the piston of the booster cylinder reaches the limit position while the piston of the steering cylinder does not reach the limit position, the oil passage on / off valve will be opened to connect the small piston cylinder and the large piston cylinder, thereby achieving a compensation effect.

[0095] 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 construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0096] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0097] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. A steering hydraulic system characterized by comprising: The steering hydraulic system includes: The steering gear (5) is provided with a first oil outlet (A) and a second oil outlet (B); A steering cylinder (7), wherein a first connecting oil passage (L1) is provided between the first end of the steering cylinder (7) and the first oil outlet (A), and a second connecting oil passage (L2) is provided between the second end and the second oil outlet (B); and The booster cylinder includes a first booster cylinder (61) disposed in the first connecting oil circuit (L1) and a second booster cylinder (62) disposed in the second connecting oil circuit (L2). The first booster cylinder (61) and the second booster cylinder (62) each include a small piston cylinder and a large piston cylinder located at both ends. The piston area ratio between the large piston cylinder and the small piston cylinder is not less than 2. 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 chamber of the steering cylinder (7). The oil replenishment valve (9) is set in the oil replenishment and balance oil circuit between the small piston cylinder of the first booster cylinder (61) and the small piston cylinder of the second booster cylinder (62).

2. The steering hydraulic system according to claim 1, characterized by The oil replenishment valve (9) is an electromagnetic directional valve.

3. The steering hydraulic system according to claim 2, characterized by The steering hydraulic system also includes: The pressure sensor includes a first pressure sensor disposed in the small piston cylinder of the first booster cylinder (61) and a second pressure sensor disposed in the small piston cylinder of the second booster cylinder (62); The controller is configured as follows: The detected pressure difference between the first pressure sensor and the second pressure sensor is determined to be greater than a preset pressure difference value; Control the replenishing valve (9) to open the replenishing balance oil circuit.

4. The steering hydraulic system according to claim 2, characterized by The replenishing valve (9) is a three-position four-way directional valve with O-type center position function.

5. The steering hydraulic system according to any one of claims 1 to 4, characterized by The piston assembly of the booster cylinder includes a small piston in the small piston cylinder, a large piston in the large piston cylinder, and a piston connecting oil passage for connecting the two cylinder chambers. The piston connecting oil passage is provided with an oil passage on / off valve.

6. The steering hydraulic system according to claim 5, characterized by The piston assembly includes a piston linkage shaft (6) that rigidly connects the small piston and the large piston. The piston linkage shaft (6) is a hollow shaft and a one-way shut-off valve (8) serving as the oil passage on / off valve is provided in the hollow shaft cavity. The one-way shut-off valve (8) is configured to allow hydraulic oil to flow from the large piston cylinder to the small piston cylinder and to shut off in the reverse direction.

7. The steering hydraulic system according to claim 5, wherein The oil passage on / off valve is an electromagnetic switch valve (10).

8. The steering hydraulic system according to claim 7, characterized by The steering hydraulic system also includes: The piston stroke switch includes a first piston stroke switch disposed in the small piston cylinder and a second piston stroke switch disposed in the cylinder chamber of the steering cylinder (7); The controller is configured as follows: It is confirmed that the first piston limit switch has been triggered; It was determined that the second piston limit switch was not triggered; The control opens the oil passage on / off valve to connect the piston to the oil passage.

9. The steering hydraulic system according to claim 5, wherein The piston assembly is a stepped shaft with an integral structure.

10. The steering hydraulic system of claim 1, wherein, The steering hydraulic system also includes: Hydraulic pump (2); Priority valve (4) is used to distribute the pumping hydraulic oil of the hydraulic pump (2) to the steering gear (5) which has a manual pump function.

11. A fork lift truck comprising a rear mounted steered axle characterised in that, The forklift also includes a steering hydraulic system according to any one of claims 1 to 10, wherein the steering cylinder (7) acts on the steering axle.

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