Forklift hydraulic valve group and forklift hydraulic system

Abstract

Provided are a forklift hydraulic valve group, comprising two main valves, each of which has a first control end on an axial first side and a second control end on an axial second side, wherein the first control end is subjected to a pilot pressure, and the second control end is subjected to at least a return spring; each of the main valves has a first oil port and a second oil port, and in a neutral valve position, the first oil port is not communicated with the second oil port, and in a working valve position, the first oil port is communicated with the second oil port at a controlled opening degree; and a pilot valve, which is an electric proportional valve, has an oil inlet connected to a pilot oil port and an oil outlet connected to at least the first control end of each of the main valves. The first oil ports of the two main valves are connected to a pressure oil port, and the second oil ports of the two main valves are respectively connected to corresponding oil cylinder interfaces and communicated with each other. A forklift hydraulic system comprising the forklift hydraulic valve group is also provided. The stability of the forklift fork when descending at a low speed and the energy recovery efficiency when descending at a high speed and under heavy load can be improved.

Description

Technical Field

[0001] This application relates to the field of forklift energy recovery technology, and more particularly to a forklift hydraulic valve assembly capable of performing forklift energy recovery and a forklift hydraulic system using such a valve assembly. Background Technology

[0002] During forklift operation, the forks frequently lift and lower heavy objects (such as palletized goods). For forklifts without an energy recovery system, the gravitational potential energy during fork lowering is usually wasted as heat energy through the throttling of the hydraulic system's main valve return oil, sometimes leading to increased hydraulic oil temperature and system aging. Therefore, some forklifts are equipped with energy recovery systems to recover the gravitational potential energy during fork lowering. However, existing forklift energy recovery technologies still have some problems. For example, when the forks are lowered at low speed, the speed of the fixed displacement gear motor is low, resulting in very low motor efficiency and low energy conversion efficiency. Even when the forks are lightly loaded, insufficient energy causes the conversion device to frequently start and stop, affecting the stability of the fork descent. Considering these reasons, some energy recovery systems do not recover energy during low-speed fork descent, acting purely as a throttling system. However, the valve core lacks hydraulic compensation, leading to unstable descent speed. Furthermore, under heavy-load, high-speed conditions, the solenoid valve is fully open. Due to the limited oil flow capacity of the solenoid valve, the pressure loss of the oil passing through it is significant, consuming a considerable amount of energy. Utility Model Content

[0003] The purpose of this application is to provide a forklift hydraulic valve group and a forklift hydraulic system that can improve the stability of the forks during low-speed descent and the energy recovery efficiency during high-speed heavy-load descent.

[0004] Therefore, this application provides a forklift hydraulic valve assembly in one aspect, comprising: two main valves, each main valve having a first control end on a first axial side and a second control end on a second axial side, wherein the first control end is subjected to pilot pressure and the second control end is subjected to at least a return spring; each main valve has a first port and a second port, wherein in a neutral valve position, the first port and the second port are not connected, and in a working valve position, the first port and the second port are connected with a controlled opening; and a pilot valve, which is an electro-proportional valve, wherein its inlet is connected to the pilot port and its outlet is connected to at least the first control end of each main valve; wherein the first ports of the two main valves are connected to pressure ports, and the second ports of the two main valves are respectively connected to corresponding cylinder interfaces and are connected to each other.

[0005] In one embodiment, the two main valves are integrated into a common valve body and each includes a valve core that moves axially within the valve body.

[0006] In one embodiment, each valve core includes an annular oil groove defined between a first shaft segment on a first axial side and a second shaft segment on a second axial side, the first shaft segment and the second shaft segment having equal cross-sectional areas.

[0007] In one embodiment, each valve core includes a plurality of channels extending from an annular oil groove toward the circumferential surface of the second shaft segment, the axial flow area of ​​each channel decreasing from the annular oil groove toward the circumferential surface of the second shaft segment.

[0008] In one embodiment, the first end of the first side of the axial direction of each valve core is arranged in a corresponding pilot cavity in the valve body, the two pilot cavities are connected to each other and are respectively connected to the oil outlet of the pilot valve via a first throttle.

[0009] In one embodiment, the second end of the second side of the axial direction of each valve core is arranged in a corresponding spring cavity in the valve body and is pushed by a corresponding return spring arranged in the spring cavity.

[0010] In one embodiment, the two spring chambers are connected to each other and are respectively connected to the oil outlet of the pilot valve via a second throttle, and each second throttle is pushed against the end face of the second end of the corresponding valve core by a corresponding return spring.

[0011] In one implementation, the spring force of each return spring is adjustable.

[0012] In another aspect, this application provides a forklift hydraulic system, comprising: a pair of drive cylinders for driving forks; a main pump capable of operating in motor mode during energy recovery; a pilot oil source; a generator; and the forklift hydraulic valve assembly of this application; wherein the output port of the main pump is connected to the pressure port; the oil chambers of the pair of drive cylinders are respectively connected to corresponding cylinder interfaces; the pilot oil source is connected to the pilot port; and the generator is connected to the main pump.

[0013] In one embodiment, the generator is composed of the drive motor of the main pump.

[0014] In one embodiment, the forklift hydraulic valve assembly has an energy recovery mode, in which the value of the pilot pressure output by the pilot valve is related to the fork lowering speed.

[0015] The forklift hydraulic valve group and forklift hydraulic system of this application can take into account both low-speed stable control and high-speed efficient recovery of potential energy during the forklift fork descent. It realizes the function of valve-controlled speed stabilization during low-speed descent and full valve opening to reduce pressure loss and recover energy during high-speed descent, avoiding the problems of low efficiency of forklift gravitational potential energy recovery and poor low-speed stability in the prior art. Attached Figure Description

[0016] The foregoing and other aspects of this application will be more fully understood through the following detailed description with reference to the accompanying drawings, in which: Figure 1 This is the hydraulic circuit diagram of the forklift hydraulic valve assembly of this application; Figure 2 This is the hydraulic circuit diagram of the forklift hydraulic valve group in energy recovery mode according to this application; Figure 3 This is a cross-sectional view of the main valve in the forklift hydraulic valve assembly of this application; Figure 4 , Figure 5 They are Figure 4 The front view and perspective view of the main valve in the diagram. Detailed Implementation

[0017] This application relates to a forklift fork gravity potential energy recovery technology based on hydraulic valve group control, applicable to energy recovery and reuse during the fork descent process in warehousing, logistics, and other scenarios. To this end, this application provides a forklift hydraulic system with energy recovery functionality.

[0018] The forklift's hydraulic system includes: The actuator is a pair of hydraulic cylinders used to drive the forks; The power source is the main pump, such as a piston pump, which can operate as a motor during energy recovery. The pilot oil source can be a separately installed pilot pump, or it can be provided by depressurization of the oil pressure output from the main pump branch; Power conversion devices, including generators and energy storage units; and Figure 1 The hydraulic valve assembly shown.

[0019] The generator can be a standalone generator driven by the main pump. Alternatively, the generator can be a drive motor of the main pump, which operates as a generator during energy recovery. For example, the drive motor of the main pump is an integrated electric motor-generator. The energy storage unit is a battery or supercapacitor that receives and stores the electrical energy generated by the generator.

[0020] It should be noted that in this application, the hydraulic cylinder, main pump, generator and energy storage unit can all be existing products, so they will not be shown or described here.

[0021] Go to Figure 1 The hydraulic valve assembly used in the forklift hydraulic system of this application includes: main valve 1, main valve 2, and pilot valve 3. The hydraulic valve assembly is equipped with: cylinder interfaces C1 and C2, pressure port P, return port L, measuring port MC, and pilot port PIL.

[0022] Cylinder ports C1 and C2 are used to connect to the oil chambers of a pair of drive cylinders of the forks, respectively. Pressure port P is used to connect to the output port of the main pump. Return port L leads to the oil tank. Measuring port MC is used to connect a pressure gauge to measure the load pressure. Pilot port PIL is used to connect to the pilot oil source. Cylinder ports C1 and C2 are connected, and measuring port MC is connected between cylinder ports C1 and C2.

[0023] Main valves 1 and 2 have the same structure. Each main valve 1 and 2 is a two-position two-way valve, with two valve positions and two oil ports. The two oil ports are the first oil port and the second oil port, respectively. The first oil port of both main valves 1 and 2 is connected to the pressure oil port P, and the second oil ports of both main valves 1 and 2 are connected to the cylinder interfaces C1 and C2, respectively.

[0024] The two valve positions of main valves 1 and 2 are respectively Figure 1 The neutral valve position shown and Figure 2 The diagram shows the operating valve positions. In the neutral position, the connection between the first and second ports is cut off. In the operating position, the first and second ports are connected with a variable opening. Each main valve 1, 2 has a first control terminal and a second control terminal. The first control terminal is subjected to pilot pressure from the pilot valve 3. The second control terminal is subjected to the combined action of the return spring and the pilot pressure from the pilot valve 3. The spring force of the return spring is adjustable.

[0025] Pilot valve 3 is an electro-proportional pressure reducing valve. Its inlet is connected to the pilot port PIL via an oil filter, its outlet connects to main valves 1 and 2, and its drain port connects to the return port L. The ratio of the pilot pressure output by pilot valve 3 to the pilot port PIL pressure depends on the magnitude of the control current applied to pilot valve 3. The hydraulic oil output from the outlet of pilot valve 3 is branched. The first branch is throttled by the first throttle 4 and connected to the first control terminals of main valves 1 and 2. The second branch is throttled by the second throttle 5 and connected to the second control terminals of main valves 1 and 2. When no pilot pressure is supplied to the main valves, the main valves are in the neutral position. When the pilot pressure at the first control terminal of the main valves overcomes the return spring and the pilot pressure at the second control terminal, the main valves are switched to the working position. In the working position, the opening degree of the main valves is positively correlated with the pilot pressure supplied to the main valves. Throttling devices 4 and 5 can be integrated with main valves 1 and 2.

[0026] It should be noted that supplying pilot pressure to both control terminals of main valves 1 and 2 ensures stable valve core movement and stable hydraulic oil flow through main valves 1 and 2. However, supplying pilot pressure to the second control terminal of main valves 1 and 2 is not necessary. According to other feasible embodiments, pilot pressure can be supplied only to the first control terminal of main valves 1 and 2.

[0027] When main valves 1 and 2 are in the neutral position, such as Figure 1As shown, their respective first and second oil ports are not connected. At this time, the hydraulic system can be in a non-operating state or in a pressure-holding state during operation.

[0028] When the main control valves 1 and 2 are switched to the working position, such as Figure 2 As shown, their respective first and second oil ports are connected. The hydraulic system is in operation at this time. When the forks need to be raised, the main pump is controlled to output hydraulic oil. The hydraulic oil enters the hydraulic valve group through the pressure port P, and flows sequentially through the first and second oil ports of main valves 1 and 2, and cylinder interfaces C1 and C2, supplying hydraulic oil to the drive cylinders and driving the forks to rise. When the forks need to be lowered, the main pump is controlled to operate in motor mode. The forks descend, causing one or both drive cylinders to retract. The hydraulic oil in the drive cylinders enters the hydraulic valve group through cylinder interfaces C1 and / or C2, and flows through the second and first oil ports of main valves 1 and / or 2, and pressure port P to the main pump in motor mode. If the fork lowering speed exceeds a set speed limit (as described later), the hydraulic module is controlled to enter energy recovery mode. The main pump in motor mode drives the generator to generate electricity, recovering the potential energy of the lowered forks.

[0029] A feasible structure for main valves 1 and 2 is in Figure 3 As shown in the diagram, the main valves 1 and 2 are integrated into one unit, comprising a common valve body 11 and valve cores 12 arranged parallel to each other within the valve body 11. Each valve core 12 can move axially and controllably within the valve body 11.

[0030] Figure 3 The image shows main valves 1 and 2 in the neutral valve position. The valve body 11 contains: a pressure oil chamber 13 connected to the pressure oil port P; two branch oil chambers 14 connected to each other and respectively connected to cylinder interfaces C1 and C2; two pilot chambers 15 connected to each other and respectively connected to the outlet of pilot valve 3 via throttle 4; and two spring chambers 16 connected to each other and respectively connected to the outlet of pilot valve 3 via throttle 5.

[0031] The specific structure of each valve core 12 is as follows: Figure 4 , Figure 5 As shown in the diagram, the valve core 12 has a first end 12a located on a first axial side (corresponding to the first control end of the main valve) and a second end 12b located on a second axial side (corresponding to the second control end of the main valve). A section of the valve core 12 forms an annular oil groove 12c in the form of a countersunk groove. The annular oil groove 12c is defined between a first shaft segment 12d on the first axial side and a second shaft segment 12e on the second axial side. The shaft segments 12d and 12e have equal cross-sectional areas in a plane perpendicular to the axial direction; specifically, they are cylindrical segments with equal diameters.

[0032] A plurality of axially extending channels 12f are formed from the annular oil groove 12c toward the circumferential surface of the shaft segment 12e. The axial flow area of ​​each channel 12f generally decreases from the annular oil groove 12c toward the circumferential surface of the shaft segment 12e, thereby forming the maximum total flow area at the port of each channel 12f that communicates with the annular oil groove 12c, and the minimum total flow area at the end that intersects with the circumferential surface of the shaft segment 12e.

[0033] Combination Figure 4 , Figure 5 See Figure 3 Each valve core 12 has a first end 12a located in a corresponding pilot chamber 15, in which a throttle 4 is arranged. The throttle 4 is used to throttle between the pilot chamber 15 and the oil outlet of the pilot valve 3. The second end 12b of each valve core 12 is located in a corresponding spring chamber 16 and is pushed by a corresponding return spring 17 arranged in the spring chamber 16 via a throttle 5. The throttle 5 is used to throttle between the second end 12b of the valve core 12 and the oil outlet of the pilot valve 3. Because the throttle 5 is pushed axially towards the first side by the return spring 17 against the second end 12b of the valve core 12, the second end 12b and the throttle 5 remain in close contact. Only the portion of the end face of the second end 12b facing the throttle orifice of the throttle 5 receives the pilot pressure. On the other hand, the first end 12a of the valve core 12 does not contact the throttle 4. In this way, the area of ​​the first end 12a of the valve core 12 subjected to pilot pressure is greater than the area of ​​the second end 12b subjected to pilot pressure, so that the force of the pilot pressure supplied by the pilot valve 3 to the first control end of each main valve on the valve core 12 (towards the second axial side) is greater than the force of the pilot pressure supplied to the second control end of each main valve on the valve core (towards the first axial side).

[0034] In the neutral valve position, the annular oil groove 12c of each valve core 12 is connected to the corresponding branch oil chamber 14, and the shaft segment 12e separates the branch oil chamber 14 from the pressure oil chamber 13.

[0035] When the pilot valve 3 applies pilot pressure to the main valves 1 and 2, the force generated by the pilot pressure on the first end 12a of the valve core 12 is greater than the sum of the force generated by the pilot pressure on the second end 12b and the force of the return spring 17. Therefore, the valve core 12 is pushed towards the second axial side, so that the channel 12f comes to the position of communicating with the pressure oil chamber 13. Thus, the channel 12f establishes a connection between the pressure oil chamber 13, the annular oil groove 12c, and the branch oil chamber 14, so that the hydraulic oil can flow from the branch oil chamber 14 to the pressure oil chamber 13 or from the pressure oil chamber 13 to the branch oil chamber 14.

[0036] During pressure holding, the hydraulic pressure from the drive cylinder is transmitted to the corresponding branch oil chamber 14 via cylinder interfaces C1 and C2, thereby establishing high pressure in the branch oil chamber 14. Since the cross-sectional areas of shaft segments 12d and 12e are equal, the axial forces exerted by the hydraulic pressure in the branch oil chamber 14 on shaft segments 12d and 12e are equal. The high pressure in the branch oil chamber 14 will not cause the valve core 12 to be axially pushed and accidentally open the main valve. This feature ensures that during pressure holding, sudden pressure changes in the drive cylinder will not cause the main valve to open due to pressure fluctuations in the drive cylinder.

[0037] When the forks are lowered, after the valve core 12 moves axially, causing the channel 12f to initially connect with the pressure oil chamber 13, the oil pressure on the shaft section 12e side becomes lower than the oil pressure on the shaft section 12d side. This pressure difference exerts a force on the valve core 12 in the direction tending to close the main valve. Through this feature, a dynamic balance of the main valve's "open-throttling-closing tendency" can be achieved, enabling the main valve to provide stable throttling control and preventing sudden changes in the main valve flow rate caused by sudden pressure changes in the drive cylinder that could lead to sudden changes in the axial position of the valve core 12.

[0038] With the above-mentioned main valve structure, stable control accuracy can be maintained under different loads and flow rates. Especially under low-speed and low-flow conditions, it effectively avoids the flow fluctuation problem caused by load changes in traditional valve groups.

[0039] The hydraulic valve assembly of this application enables the recovery of potential energy during fork descent. Generally, the drive current applied to the pilot valve 3 is controlled in a positive correlation with the fork descent speed; that is, the magnitude of the pilot pressure output by the pilot valve 3 is positively correlated with the fork descent speed. Specifically, firstly, the descent action is graded based on the fork descent speed. A fork descent speed limit is set (e.g., 10 mm / s). This speed limit can be specifically set according to the specific forklift model.

[0040] When the fork lowering speed is equal to or lower than this speed limit, the fork lowering is determined to be low-speed lowering; when the fork lowering speed is higher than this speed limit, the fork lowering is determined to be high-speed heavy-load lowering.

[0041] During the low-speed lowering process, the pilot valve 3 outputs a low pilot pressure, keeping the main valves 1 and 2 at a small opening. Due to the design of the main valves 1 and 2, as long as their opening is fixed, the flow rate through them remains stable, regardless of the weight carried by the forks. This achieves a stable flow output independent of the load. At this time, the main pump operates as a motor, and the generator does not generate electricity.

[0042] During high-speed, heavy-load lowering, the pilot valve 3 outputs maximum pilot pressure, ensuring that main valves 1 and 2 are fully open. This parallel operation of the two valves reduces overall pressure loss. High-pressure hydraulic oil directly drives the main pump (in motor mode) to rotate at high speed, which in turn drives the generator to produce electricity, thus improving the effective energy recovery.

[0043] By employing the hydraulic valve assembly of this application in the hydraulic system of a forklift, the technical effects described below can be obtained.

[0044] 1. To achieve different functions under different working conditions, balancing efficiency and stability.

[0045] 1) At low speeds, the main valve is in a slightly open state. The opening of the main valve is adjusted by the proportional control function of the pilot valve, and the pressure compensation component achieves "stable flow output regardless of load". Even if the weight of the goods changes, the flow rate remains stable as long as the valve opening is fixed. At high speeds, both valves are fully open to reduce pressure loss. The motor efficiently switches between these two modes, achieving intelligent switching between "stable control at low speeds and high efficiency at high speeds".

[0046] 2) The main valve is fully open at high speeds via a pilot valve, and the total pressure loss is reduced by using a "dual-valve parallel" design. High-pressure oil directly drives the hydraulic motor to rotate at high speed, which in turn drives the generator to generate electricity efficiently, and the electrical energy is stored in the energy storage unit.

[0047] 2. The main valve's unique properties make it suitable for forklift applications.

[0048] 1) With hydraulic compensation function when the opening is small: ensures the linear relationship between the main valve opening and the flow rate under different loads (cargo weights) and improves control accuracy; the steady-state hydraulic force will increase with the increase of load pressure, and the direction is always "the valve opening tends to close smaller", and the flow rate through the valve opening is independent of the load size; 2) When in the neutral position, the main valve is not connected between the first and second oil ports (low-pressure isolation): This prevents oil leakage in non-recovery conditions and reduces standby power consumption; 3) Integrated proportional control: Enables continuous adjustment of the main valve flow rate.

[0049] 3. Strong system compatibility.

[0050] 1) It can be directly integrated into the existing forklift hydraulic system without major modifications; 2) The hydraulic compensation design of the main valve can be extended to scenarios such as explosion-proof valve cores, improving the versatility of the technology.

[0051] 4. Stable pilot pressure control.

[0052] The electro-proportional pressure reducing valve can proportionally adjust the control pressure according to the current of the solenoid coil, and is less affected by the inlet pressure, ensuring the stability of the pilot pressure, thereby improving the control accuracy of the main valve and the energy recovery efficiency. This proportional pressure reducing valve sets a minimum pressure when power is off or the set value is 0, enhancing the safety and reliability of the system, and maintaining a basic pressure state even under special circumstances.

[0053] While some embodiments have been described above, these embodiments are given by way of example only and are not intended to limit the scope of this application. The appended claims and their equivalents are intended to cover all modifications, substitutions, and alterations made within the scope and spirit of this application.

Claims

1. A forklift hydraulic valve assembly, characterized in that, include: Two main valves (1, 2), each having a first control end on a first axial side and a second control end on a second axial side, wherein the first control end is subjected to pilot pressure, and the second control end is subjected to at least the action of a return spring; each main valve has a first oil port and a second oil port, wherein in the neutral valve position, the first oil port and the second oil port are not connected, and in the working valve position, the first oil port and the second oil port are connected with a controlled opening; and Pilot valve (3), which is an electro-proportional valve, has its inlet connected to the pilot port (PIL) and its outlet connected to at least the first control terminal of each main valve; The first oil port of the two main valves (1, 2) is connected to the pressure oil port (P), and the second oil ports of the two main valves (1, 2) are respectively connected to the corresponding cylinder interfaces (C1, C2) and are interconnected with each other.

2. The forklift hydraulic valve assembly as described in claim 1, characterized in that, The two main valves (1, 2) are integrated into a common valve body (11) and each includes a valve core (12) that moves axially within the valve body (11).

3. The forklift hydraulic valve assembly as described in claim 2, characterized in that, Each valve core (12) includes an annular oil groove (12c) defined between a first shaft segment (12d) on a first axial side and a second shaft segment (12e) on a second axial side, wherein the first shaft segment (12d) and the second shaft segment (12e) have equal cross-sectional areas.

4. The forklift hydraulic valve assembly as described in claim 3, characterized in that, Each valve core (12) includes a plurality of channels (12f) extending from an annular oil groove (12c) toward the circumferential surface of the second shaft segment (12e), the axial flow area of ​​each channel (12f) decreasing from the annular oil groove (12c) toward the circumferential surface of the second shaft segment (12e).

5. The forklift hydraulic valve assembly as described in any one of claims 2-4, characterized in that, The first end (12a) of the first side of the axial direction of each valve core (12) is arranged in the corresponding pilot chamber (15) in the valve body (11). The two pilot chambers (15) are connected to each other and are respectively connected to the oil outlet of the pilot valve (3) via the first throttle (4).

6. The forklift hydraulic valve assembly as described in claim 5, characterized in that, The second end (12b) on the second axial side of each valve core (12) is arranged in a corresponding spring cavity (16) in the valve body (11) and is pushed by a corresponding return spring (17) arranged in the spring cavity (16).

7. The forklift hydraulic valve assembly as described in claim 6, characterized in that, The two spring chambers (16) are connected to each other and are respectively connected to the oil outlet of the pilot valve (3) via the second throttle (5). Each second throttle (5) is pushed against the end face of the second end (12b) of the corresponding valve core (12) by the corresponding return spring (17).

8. The forklift hydraulic valve assembly as described in claim 7, characterized in that, The spring force of each return spring (17) is adjustable.

9. A forklift hydraulic system, comprising: A pair of hydraulic cylinders for driving the forks; The main pump can operate in motor mode during energy recovery; Pilot oil source; dynamo; The forklift hydraulic system is characterized in that it further includes: Forklift hydraulic valve assembly as described in any one of claims 1-8; The output port of the main pump is connected to the pressure oil port (P). The oil chambers of the pair of drive cylinders are respectively connected to the corresponding cylinder interfaces (C1, C2). The pilot oil source is connected to the pilot oil port (PIL); The generator is connected to the main pump.

10. The forklift hydraulic system as described in claim 9, characterized in that, The generator is composed of the drive motor of the main pump.

11. The forklift hydraulic system as described in claim 9 or 10, characterized in that, The forklift hydraulic valve group has an energy recovery mode, in which the value of the pilot pressure output by the pilot valve (3) is related to the fork lowering speed.

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