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 gear provided with a first oil outlet and a second oil outlet; a first connecting oil way is arranged between the first end of the steering oil cylinder and the first oil outlet, and a second connecting oil way is arranged between the second end of the steering oil cylinder and the second oil outlet; the pressurizing cylinders comprise the first pressurizing cylinder arranged in the first connecting oil way and the second pressurizing cylinder arranged in the second connecting oil way, the first pressurizing cylinder and the second pressurizing cylinder each comprise a small piston cylinder and a large piston cylinder which are located at the two ends, the large piston cylinders are hydraulically connected with an oil outlet of the steering gear, and the small piston cylinders are hydraulically connected with an oil cylinder cavity of the steering oil cylinder; the oil supplementing valve is arranged on an oil supplementing balance oil way between the small piston cylinder of the first pressure cylinder and the small piston cylinder of the second pressure cylinder. By additionally arranging the pressurizing cylinder, the pressurizing driving effect can be achieved, steering is more convenient and flexible, and by arranging the oil supplementing valve, oil balance of the oil cylinders on the two sides can be achieved in time.

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] In industrial sites such as warehouses, ports, and factories, forklifts are often needed as industrial handling vehicles for loading and unloading, stacking, and short-distance transportation of goods. When the forklift is operating, the front end is loaded, and timely and flexible steering operations are required. However, under certain working conditions, such as idling, internal leakage, and fast steering speeds, heavy steering is often prone to problems, making the driver's operation difficult, 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, but because 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, making it impossible to steer in an emergency. Summary of the Invention

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

[0004] To achieve the above objectives, the present application provides a steering hydraulic system, which includes: A steering gear having a first oil outlet and a second oil outlet; a steering cylinder, wherein a first connecting oil passage is provided between a first end of the steering cylinder and the first oil outlet, and a second connecting oil passage is provided between a second end of the steering cylinder and the second oil outlet; and a booster cylinder, comprising a first booster cylinder disposed in the first connecting oil circuit and a second booster cylinder disposed in the second connecting oil circuit, wherein the first booster cylinder and the second booster cylinder each comprise a small piston cylinder and a large piston cylinder located at both ends, the large piston cylinder being hydraulically connected to an oil outlet of the steering gear, and the small piston cylinder being hydraulically connected to an oil cylinder chamber of the steering oil cylinder; The oil replenishing valve is arranged in the oil replenishing balancing oil circuit between the small piston cylinder of the first boosting cylinder and the small piston cylinder of the second boosting cylinder.

[0005] In some embodiments, the oil replenishment valve is a solenoid reversing valve.

[0006] In some embodiments, the steering hydraulic system further comprises: The pressure sensors include a first pressure sensor disposed in the small piston cylinder of the first boosting cylinder and a second pressure sensor disposed in the small piston cylinder of the second boosting cylinder; The controller is configured as: Determining that a detected pressure difference value between the first pressure sensor and the second pressure sensor is greater than a preset pressure difference value; The oil replenishment valve is controlled to open the oil replenishment balancing oil circuit.

[0007] In some embodiments, the oil replenishment valve is a three-position four-way reversing valve with an O-type center position function.

[0008] In some embodiments, the piston assembly of the booster cylinder includes a small piston located in the small piston cylinder, a large piston located in the large piston cylinder, and a piston connecting oil channel for connecting the cylinder cavities at both ends, and an oil channel on-off valve is provided in the piston connecting oil channel.

[0009] In some embodiments, the piston assembly includes a piston linkage shaft rigidly connecting the small piston and the large piston. The piston linkage shaft is a hollow shaft. A one-way stop valve serving as the oil channel on-off valve is provided in the hollow shaft cavity. The one-way stop valve is configured to allow hydraulic oil to flow from the large piston cylinder to the small piston cylinder and to cut off the flow in the opposite direction.

[0010] In some embodiments, the oil channel on-off valve is an electromagnetic switch valve.

[0011] 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.

[0012] In some embodiments, the piston assembly is a stepped shaft of an integral structure.

[0013] 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.

[0014] 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.

[0015] In the technical solution of the present application, booster cylinders are added to the two connecting oil circuits between the steering gear and the steering cylinder, that is, a first and a second booster cylinder are added, so that the hydraulic oil with low pressure can drive the steering cylinder by driving the booster cylinder, thereby achieving a booster drive effect and improving the pressure output of the hydraulic system, thereby significantly reducing the force of the steering operation and making the steering more convenient and flexible. Moreover, by providing an oil replenishment valve in the oil replenishment balance oil circuit between the small piston cylinder of the first booster cylinder and the small piston cylinder of the second booster cylinder, it can be used to achieve oil balance in the cylinders on both sides in a timely manner. Therefore, 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.

[0016] 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

[0017] 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 Hydraulic principle diagram of the oil replenishment valve used in; Figure 3 for Figure 1 A schematic diagram of the structure of the booster cylinder used in the embodiment of the present invention; Figure 4 is a complete hydraulic principle diagram of a steering hydraulic system according to a first embodiment of the present application; Figure 5 A partial hydraulic principle diagram of a steering hydraulic system according to a second embodiment of the present application; Figure 6 for Figure 5 Schematic diagram of the structure of the booster cylinder used in.

[0018] Description of Reference Numerals DETAILED DESCRIPTION

[0019] 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.

[0020] A forklift and a steering hydraulic system thereof according to the present application will be described below with reference to the accompanying drawings.

[0021] This application discloses a new type of steering hydraulic system. Figure 1 As shown, in this embodiment, the steering hydraulic system includes: 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 path L1 is provided between a first end of the steering cylinder 7 and the first oil outlet A, and a second connecting oil path L2 is provided between a second end of the steering cylinder 7 and the second oil outlet B; and The boosting cylinder includes a first boosting cylinder 61 provided in the first connecting oil circuit L1 and a second boosting cylinder 62 provided in the second connecting oil circuit L2. The first boosting cylinder 61 and the second boosting cylinder 62 each 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 5, and the small piston cylinder is hydraulically connected to the cylinder chamber of the steering cylinder 7. The oil replenishment valve 9 is provided in the oil replenishment balancing oil circuit between the small piston cylinder of the first boosting cylinder 61 and the small piston cylinder of the second boosting cylinder 62 .

[0022] This application first increases the pressure output of the hydraulic system by adding a booster cylinder, thereby significantly reducing the force of the steering operation and making the steering more light and flexible. Figure 1 As shown, the key to the innovative introduction of booster cylinders lies in placing two booster cylinders in series between the outlet of the steering gear 5 and the steering cylinder 7, forming a nearly closed circuit. Hydraulic oil at the outlet of the steering gear 5 first drives the booster cylinders, which then drive the steering cylinder 7, achieving twice the result with half the effort. Even with low output pressure, the steering cylinder 7 can be smoothly driven, solving the problem of heavy steering.

[0023] like Figure 3 As shown, the booster cylinder generally includes small piston cylinders located at both ends (i.e. Figure 3 The upper end of the booster cylinder) and the large piston cylinder (i.e. Figure 3The 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.

[0024] like Figure 4 As shown, the steering hydraulic system of a forklift is generally composed of a hydraulic pump 2, a priority valve 4, a steering gear 5, a steering cylinder 7, etc., wherein the hydraulic pump 2 serves as a power source to supply oil to the system, the priority valve 4 distributes the hydraulic oil, the steering gear 5 serves as a core control component to play a control and metering role, and the steering cylinder 7 serves as an actuator. The outlet of the steering gear 5 is connected to the steering cylinder 7. When there is an internal leakage, the steering wheel is turned too fast, and the hydraulic oil is insufficient, it is easy to cause the steering to be heavy, causing the driver to operate with difficulty, affecting the driving experience and safety. By providing a first boost cylinder 61 and a second boost cylinder 62, not only can the problem of heavy steering be solved, but the response speed and stability of the system can also be improved, ensuring the accuracy and reliability of steering under complex working conditions. At the same time, it can also optimize the energy utilization efficiency of the hydraulic system, reduce unnecessary energy loss, extend the service life of the system, and reduce maintenance costs, bringing multiple benefits to the steering system.

[0025] Secondly, in addition to the additional booster cylinder, this application also provides Figure 2 The oil replenishing valve 9 shown in the figure is arranged in the oil replenishing balance oil circuit between the small piston cylinder of the first boosting cylinder 61 and the small piston cylinder of the second boosting cylinder 62. The oil replenishing balance 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 This is because in actual operation, the hydraulic oil capacities of the first and second booster cylinders on both sides may be different. By setting the oil replenishment valve 9, it can be used to control the on-off of the oil replenishment balance oil circuit to achieve oil balance in the cylinders on both sides.

[0026] The oil replenishment balance oil circuit is used to hydraulically connect the first and second boost cylinders, and the oil replenishment valve 9 serves as an oil circuit on-off control valve. Figure 1 、 Figure 2Its working principle is as follows: Hydraulic oil is supplied from the first oil outlet A of the steering gear 5 to the first booster cylinder 61. When the first booster cylinder 61 has not reached the limit position and the steering cylinder 7 has reached the limit position, the second booster cylinder 62 has not reached the limit position either, that is, 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, the control Figure 2 When solenoid 1YA of oil-supply valve 9 is energized, the oil-supply balancing circuit is opened through oil-supply valve 9, connecting the left and right booster cylinders. This allows excess hydraulic oil in the small piston of first booster cylinder 61 to flow to the small piston of second booster cylinder 62. Once the pressure on both sides is equalized, oil-supply valve 9 is controlled to return to its neutral position, disconnecting the oil circuit. Conversely, when the right solenoid valve 2YA is energized, excess hydraulic oil in second booster cylinder 62 flows to first booster cylinder 61, thus equalizing the hydraulic pressure in both booster cylinders.

[0027] like Figure 2 As shown, the oil supply valve 9, as an example, utilizes a three-position, four-way directional control valve with an O-type neutral position function. When the electromagnets at both ends are de-energized, the three-position, four-way oil supply valve 9 is in the neutral position, or shutoff position. The three oil ports of the oil supply valve 9 are cut off from each other in the neutral position, shutting off the oil supply balancing circuit. When any one of the electromagnets is energized, the oil supply balancing circuit is opened, hydraulically connecting the first connecting oil circuit L1 and the second connecting oil circuit L2 on both sides.

[0028] Of course, those skilled in the art will appreciate that the oil supply valve 9 is not limited to the aforementioned three-position, four-way directional control valve with an O-type neutral position function. A two-position, two-way on-off valve, for example, may also be employed. The oil supply valve 9 is also not limited to a solenoid valve. A hydraulically controlled valve, etc., may also be employed. These are not further illustrated here.

[0029] In this embodiment, on the basis of the oil supply valve 9 adopting a common electromagnetic reversing valve, the steering hydraulic system may further include: Pressure sensors, including a first pressure sensor (not shown) disposed in the small piston cylinder of the first boosting cylinder 61 and a second pressure sensor (not shown) disposed in the small piston cylinder of the second boosting cylinder 62; The controller is configured as: Determining that a detected pressure difference value between the first pressure sensor and the second pressure sensor is greater than a preset pressure difference value; The oil replenishment valve 9 is controlled to open the oil replenishment balance oil circuit.

[0030] 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 pistons of the two booster cylinders, and then control the oil replenishment and balancing circuit to balance the pressures of the two booster cylinders. The preset pressure difference value can be set specifically based on the different models and specifications of the booster cylinders. In other embodiments, a travel switch can be used instead of a pressure sensor to determine whether there is a synchronization imbalance or pressure imbalance between the two booster cylinders.

[0031] It's important to note that, in practice, long-term use of oil cylinders inevitably leads to oil leakage, which can cause the strokes of the booster and steering cylinders to become out of sync and mismatched. For example, during operation, the booster cylinder's piston may have reached its end position, while the steering cylinder's piston may not have reached its end position. This can cause the steering cylinder's 7 to not fully rotate.

[0032] Therefore, in the steering hydraulic system of this embodiment, the piston assembly of the booster cylinder includes a small piston located in a small piston cylinder, a large piston located in a large piston cylinder, and a piston oil passage connecting the two cylinder chambers of the booster cylinder. The piston oil passage is also equipped with an oil passage on-off valve. This allows hydraulic oil output from the first oil outlet A or second oil outlet B of the steering gear 5 to flow sequentially through the large piston cylinder, the piston 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 lag.

[0033] 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.

[0034] In this embodiment, see Figure 1 、 Figure 3 The oil passage shutoff valve, as an example, is a one-way shutoff valve 8, which is configured to allow hydraulic oil to flow from the large piston of the booster cylinder to the small piston cylinder, but to block it in the opposite direction. When the booster cylinder's piston reaches its limit but the steering cylinder has not, the one-way shutoff valve 8 is opened forward by the hydraulic oil, providing compensation.

[0035] Because the one-way stop valve 8 has a certain amount of back pressure, for example, the elastic pressure of the compression spring that elastically presses the valve core against the one-way valve port, this back pressure can, under normal circumstances, resist the hydraulic oil in the large piston cylinder and open the one-way stop valve 8 in a positive direction. When the piston stroke of the booster cylinder reaches the extreme end position, the hydraulic oil in the large piston cylinder continues to accumulate, and the pressure gradually increases, which can resist the compression spring and open the one-way stop valve 8 in a positive direction, thereby opening the piston communication oil passage. The hydraulic oil can then flow through the large piston cylinder, the piston communication 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.

[0036] 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.

[0037] 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 5 、 Figure 6 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.

[0038] 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.

[0039] 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 1 、 Figure 3 、 Figure 5 、 Figure 6 shown.

[0040] exist Figure 3 or Figure 6 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 .

[0041] Figure 3 、 Figure 6 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.

[0042] 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.

[0043] Figure 3 、 Figure 6 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.

[0044] 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 3 、 Figure 6In 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.

[0045] The piston assembly of the booster cylinder of this application is not limited to Figure 3 、 Figure 6 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.

[0046] See also 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 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.

[0047] 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.

[0048] In summary, Figure 1 、 Figure 5 In the embodiment, a system internal oil replenishment type power steering hydraulic system is disclosed, which consists of a filter 1, a hydraulic pump 2, an oil pumping check valve 3, a priority valve 4, a steering gear 5, a booster cylinder, a steering oil cylinder 7, etc. 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, the areas of the large piston cylinder and the small piston cylinder are proportional, and the small piston cylinder is connected to the steering oil cylinder 7. On the basis of adding a booster pump, by setting an oil replenishment valve 9, the on and off of the oil replenishment valve can be controlled by detecting the pressure difference between the left and right booster cylinders. Furthermore, a piston connecting oil channel with a control valve can be added between the large piston cylinder and the small piston cylinder of the booster cylinder to supplement the oil leakage during the working process.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] In actual operation, in the case where the hydraulic oil capacities of the first and second booster cylinders on both sides may be different, the oil replenishment valve 9 can be set to control the on-off of the oil replenishment balance oil circuit to achieve oil balance in the cylinders on both sides.

[0053] The present application also adds a piston connecting oil channel and its oil channel on-off valve in the piston assembly of the booster cylinder. When the piston of the booster cylinder reaches the limit position and the piston of the steering oil cylinder has not reached the limit position, the oil channel on-off valve will be controlled to open, connecting the small piston cylinder and the large piston cylinder to achieve compensation.

[0054] 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.

[0055] 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.

[0056] 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: A steering gear (5) is provided with a first oil outlet (A) and a second oil outlet (B); A steering oil cylinder (7), wherein a first connecting oil circuit (L1) is provided between a first end of the steering oil cylinder (7) and the first oil outlet (A), and a second connecting oil circuit (L2) is provided between a second end of the steering oil cylinder (7) and the second oil outlet (B); and A boosting cylinder, comprising a first boosting cylinder (61) arranged in the first connecting oil circuit (L1) and a second boosting cylinder (62) arranged in the second connecting oil circuit (L2), wherein the first boosting cylinder (61) and the second boosting cylinder (62) each comprise 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 (5), and the small piston cylinder being hydraulically connected to the oil cylinder chamber of the steering oil cylinder (7); An oil replenishment valve (9) is provided in an oil replenishment balancing oil circuit between the small piston cylinder of the first boosting cylinder (61) and the small piston cylinder of the second boosting cylinder (62).

2. The steering hydraulic system according to claim 1, characterized in that: The oil replenishing valve (9) is an electromagnetic reversing valve.

3. The steering hydraulic system according to claim 2, characterized in that: The steering hydraulic system also includes: The pressure sensor comprises a first pressure sensor provided in the small piston cylinder of the first boosting cylinder (61) and a second pressure sensor provided in the small piston cylinder of the second boosting cylinder (62); The controller is configured as: Determining that a detected pressure difference value between the first pressure sensor and the second pressure sensor is greater than a preset pressure difference value; The oil replenishment valve (9) is controlled to conduct the oil replenishment balance oil circuit.

4. The steering hydraulic system according to claim 2, characterized in that: The oil replenishing valve (9) is a three-position four-way reversing valve with an O-type neutral position function.

5. The steering hydraulic system according to any one of claims 1 to 4, characterized in that: The piston assembly of the booster cylinder includes a small piston located in the small piston cylinder, a large piston located in the large piston cylinder, and a piston communicating oil passage for communicating the cylinder chambers at both ends. An oil passage on-off valve is provided in the piston communicating oil passage.

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

7. The steering hydraulic system according to claim 5, characterized in that: The oil channel on-off valve is an electromagnetic switch valve (10).

8. The steering hydraulic system according to claim 7, characterized in that: The steering hydraulic system also includes: A piston travel switch, comprising a first piston travel switch arranged in the small piston cylinder and a second piston travel switch arranged in the cylinder cavity of the steering cylinder (7); 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.

9. The steering hydraulic system according to claim 5, characterized in that: The piston assembly is a stepped shaft with an integrated structure.

10. 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.

11. A forklift truck comprising a rear-mounted steering axle, characterized in that: The forklift further comprises 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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