Forklift lifting buffering hydraulic circuit

Abstract

The invention discloses a forklift lifting buffer hydraulic circuit which comprises a main control valve, a hydraulic circuit, a hydraulic circuit, a hydraulic circuit and a hydraulic control system, and the main control valve is connected with a lifting oil cylinder; the main control valve is connected with a pilot control valve; the main control valve is connected with an electric proportional overflow valve and a second overflow valve which are connected in sequence, the electric proportional overflow valve is connected with the lifting oil cylinder, and the second overflow valve is provided with a third port connected with the pilot control valve; the electric proportional overflow valve is provided with a first opening and a second opening, and the first opening is connected with a fifth opening formed in the second overflow valve; the second opening is connected with a fourth opening formed in the second overflow valve; the lifting oil cylinder is provided with a proximity switch for controlling conduction of the first opening and the second opening, and when the first opening and the second opening are conducted, the fifth opening releases pressure to conduct the third opening and the fourth opening; the valve element of the second overflow valve is moved through the electromagnetic overflow valve, pressure relief buffering can be conducted on different working states of the pilot control valve, and therefore the hydraulic process can be buffered at any time and at any degree besides threshold buffering.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulic press control circuits, and in particular to a forklift lifting buffer hydraulic circuit. Background Art

[0002] Generally, in the hydraulic system of a forklift, the actuator is a hydraulic cylinder, and the moving piston of the hydraulic cylinder will impact the cylinder barrel when it reaches the end position. However, since the inner mast is rigidly connected to the piston rod of the lifting cylinder, when the lifting cylinder drives the mast to rise to the top and is under heavy load, the impact will cause huge safety hazards.

[0003] For example, a "hydraulic control system integrating drive and buffering" disclosed in Chinese patent literature, with the announcement number: CN115306799A, includes a power circuit, a drive and buffering control circuit and an actuator; the power circuit includes a ball valve, an oil tank, a liquid level sensor and a temperature sensor, and the oil tank is sequentially provided with a liquid level sensor, a temperature sensor and a liquid level thermometer, the oil inlet end of the ball valve is connected to the oil outlet end of the oil tank, the output end of the motor is connected to the plunger pump, and the oil inlet end of the plunger pump is connected to the oil outlet end of the oil tank. However, this solution requires an additional pressure relief system and relies on the status detection of the hydraulic oil tank for buffering. Summary of the invention

[0004] In order to solve the problem that hydraulic oil is difficult to release pressure and buffer in the prior art, the present invention provides a forklift lifting buffer hydraulic circuit, which releases the pilot control oil through an electric proportional relief valve, thereby shifting the valve core of the main control valve to achieve lifting buffer of the mast.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: A forklift lifting buffer hydraulic circuit, comprising: a main control valve, the main control valve is connected to a lifting oil cylinder, the main control valve controls the pressure oil to the lifting oil cylinder; the main control valve is connected to a pilot control valve, the pilot control valve controls the pilot control oil; The main control valve is connected to an electric proportional relief valve and a second relief valve which are connected in sequence, the electric proportional relief valve is connected to the lifting cylinder, and the second relief valve is provided with a third port connected to the pilot control valve; The electric proportional relief valve is provided with a first port and a second port, wherein the first port is connected to the fifth port provided on the second relief valve; and the second port is connected to the fourth port provided on the second relief valve; The lifting oil cylinder is provided with a proximity switch for controlling the connection between the first port and the second port. When the first port and the second port are connected, the fifth port releases pressure to connect the third port and the fourth port. Under normal conditions, the pressure between the third port and the fourth port of the second relief valve is balanced. When the pressure is released, the valve core of the second relief valve is shifted by the electromagnetic relief valve, so that the third port and the fourth port of the second relief valve can respectively release pressure and buffer different working states of the pilot control valve, so that in addition to the threshold buffering, the hydraulic process can also be buffered to any degree at any time.

[0006] Preferably, the proximity switch comprises an upper proximity switch and a lower proximity switch arranged in sequence, the upper proximity switch sends a first proximity signal, and the lower proximity switch sends a second proximity signal. The upper proximity switch and the lower proximity switch send buffer control at different positions.

[0007] Preferably, the main control valve is connected to an overflow control unit, which controls the pilot control oil flowing to the valve core inside the main control valve; the overflow control unit controls the release of the pilot control oil according to the signal of the proximity switch. The overflow control unit is used to control the valve core position of the main control valve through the pilot control oil.

[0008] Preferably, the pilot control valve is located in the overflow control part, and the pilot control valve includes a first pilot control valve and a second pilot control valve respectively connected to the main control valve, and the first pilot control valve and the second pilot control valve respectively control the pilot control oil to enter the valve core of the main control valve from different directions. The first pilot control valve and the second pilot control valve are used to respectively realize the displacement of the valve core of the main control valve in different directions, thereby performing different working modes.

[0009] Preferably, the overflow control unit includes an overflow passage connected to the main control valve, the overflow passage is connected to the second overflow valve, and the overflow passage is connected to the first pilot control valve and the second pilot control valve respectively. The pilot control oil in the hydraulic circuit is discharged through the overflow passage, thereby adjusting the valve core position of the main control valve.

[0010] Preferably, the second overflow valve opens different overflow paths according to different signals of the proximity switch; when the overflow paths are opened, the pilot control oil in the pilot control valve is released, so as to realize different releases for different hydraulic processes.

[0011] As a preferred embodiment, a pilot oil source valve is included, the pilot oil source valve is connected to the pilot control valve and the second relief valve respectively, the pilot oil source valve outputs pilot control oil, and the pilot control oil is obtained through the pilot oil source valve.

[0012] Preferably, the main control valve is connected to a hydraulic oil unit, and the hydraulic oil unit inputs hydraulic oil to the valve core inside the main control valve; the main control valve is provided with a PD port connected to the hydraulic oil unit, and the hydraulic oil unit inputs pressure oil from the PD port to the main control valve. The hydraulic oil is delivered to the valve core of the main control valve through the hydraulic oil unit.

[0013] Preferably, the hydraulic oil unit includes an oil pump for inputting hydraulic oil to the main control valve, the oil pump is connected to a hydraulic oil tank, and the hydraulic oil tank stores pressurized oil. The hydraulic oil is obtained through the oil pump.

[0014] Preferably, the lifting oil cylinder is connected to a mast, and the mast is rigidly connected to the piston rod inside the lifting oil cylinder; the proximity switch detects the position of the mast and sends a signal when a threshold is reached. The mast is lifted to the top for buffering, which improves the safety and comfort during work, prolongs the working life of the oil cylinder, and realizes hydraulic buffering during the operation of the forklift.

[0015] The present invention has the following advantages: (1) Under normal conditions, the pressure between the third port and the fourth port of the second relief valve is balanced. When the pressure is released, the valve core of the second relief valve is shifted by the electromagnetic relief valve, so that the third port and the fourth port of the second relief valve can respectively perform pressure relief buffering for different working states of the pilot control valve, so that in addition to the threshold buffering, the hydraulic process can be buffered to any degree at any time; (2) Reduce the number of parts and improve the versatility; (3) By relying on the mast to lift to the top buffering, the safety and comfort during work are improved, the working life of the cylinder is extended, and the hydraulic buffering during the operation of the forklift is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings described below are merely exemplary. A person skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0017] Figure 1 Schematic diagram of the circuit structure in the embodiment.

[0018] Figure 2 Schematic diagram of the circuit operation logic in the embodiment.

[0019] In the figure: 1-Electric proportional relief valve; 2-Second relief valve; 3-Pilot control valve; 4-Main control valve; 5-Lifting cylinder; 6-Proximity switch; 7-Pilot oil source valve; 8-Oil pump; 9-Hydraulic oil tank. DETAILED DESCRIPTION

[0020] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without making any creative work shall fall within the scope of protection of the present invention.

[0021] like Figure 1-2 As shown, in a preferred embodiment, the present invention discloses a forklift lifting buffer hydraulic circuit, including: a main control valve 4, through which the hydraulic action of the system where the circuit is located is realized, and a valve core is provided in the main control valve. When the position of the valve core in the main control valve changes, the system where the circuit is located performs different hydraulic actions. When performing different hydraulic actions, the main control valve performs different hydraulic power outputs.

[0022] The main control valve 4 is connected to a lifting cylinder 5, through which the power output of the circuit is realized, and the lifting cylinder performs lifting and lowering action control in different hydraulic power outputs. The lifting cylinder includes a piston rod, and there is a lifting cylinder cavity in the lifting cylinder. The piston rod is provided with a piston, and the piston divides the lifting cylinder cavity into two parts: a rodless cavity and a rod cavity. The rodless cavity contains hydraulic oil, and the piston rod is located in the rod cavity. When the piston and the piston rod move in the lifting cylinder cavity, the volumes of the rodless cavity and the rod cavity change accordingly. When the volumes of the rodless cavity and the rod cavity change, the piston and the piston rod undergo corresponding displacements in the lifting cylinder cavity, thereby performing lifting and lowering power control through the piston rod.

[0023] The main control valve 4 controls the pressure oil to the lifting cylinder 5; the pressure oil is output and recovered through the main control valve. The rodless chamber in the lifting cylinder is connected to the main control valve, and the rodless chamber contains the pressure oil from the main control valve. When the pressure oil enters the rodless chamber of the lifting cylinder from the main control valve, the volume of the rodless chamber increases, and the piston in the lifting cylinder chamber is pushed toward the rod chamber, so that the piston rod is pushed out by the piston. When the pressure oil leaves the lifting cylinder and returns to the main control valve, the volume of the rodless chamber decreases, and the piston in the lifting cylinder chamber is pushed toward the rodless chamber, so that the piston rod is pulled back by the piston. Thereby, the piston rod is pushed.

[0024] The main control valve 4 is connected to the pilot control valve 3, and the pilot control oil is output to the main control valve through the pilot control valve. The pilot control oil is output through the pilot control valve, thereby controlling the valve core position of the main control valve, thereby realizing the change of the state of the main control valve. The pilot control valve has different input modes. When the pilot control valve is in different input modes, the working mode of the main control valve is changed.

[0025] The pilot control valve controls the pilot control oil; when the pilot control valve is turned on, the pilot control oil enters the main control valve through the pilot control valve, so that the position of the valve core in the main control valve moves in the corresponding direction. The pilot control oil controls the input and output of the oil by changing the position of the valve core.

[0026] The main control valve 4 is connected to an electric proportional relief valve 1 and a second relief valve 2 which are connected in sequence. The electric proportional relief valve obtains a signal indicating that the buffer needs to be opened. When the electric proportional relief valve receives the corresponding signal indicating that the buffer needs to be opened, the electric proportional relief valve is turned on. The electric proportional relief valve is cut off in a normal state, and the electric proportional relief valve does not affect the control of the pilot control valve over the pilot control oil in the cut-off state. When the electric proportional relief valve is in the on state, the electric proportional relief valve adjusts the state of the second relief valve. The electric proportional relief valve 1 is connected to the lifting cylinder 5, and a signal indicating the need for buffering is sent from the lifting cylinder, and the signal indicating the need for buffering is obtained from the lifting cylinder through the electric proportional relief valve. Thus, buffering of the lifting and lowering process is achieved. And the lifting cylinder can send its own working status as a signal to the electric proportional relief valve or send the moving distance corresponding to its own working status as a signal to the electric proportional relief valve. The electric proportional relief valve works according to the signal sent by the lifting cylinder as a starting signal. When the electric proportional relief valve receives the signal, it is internally conductive. When the electric proportional relief valve is internally conductive, the pressure relief of the second relief valve is opened.

[0027] The second relief valve 2 is provided with a third port connected to the pilot control valve 3; when the second relief valve is relieving pressure, the pilot control oil returned from the pilot control valve is input from the third port. Through the third port, the pilot control oil in the pilot control valve is released, thereby slowing down the hydraulic action process.

[0028] The electric proportional relief valve 1 is provided with a first port and a second port, and is also provided with an energized coil. When the energized coil is energized, the first port and the second port are connected; when the energized coil is de-energized, the first port and the second port are in a closed state.

[0029] The first port is connected to the fifth port provided in the second relief valve; the first port is communicated with the fifth port of the second relief valve. When the first port and the second port are connected, the pilot control oil is unloaded from the second port through the fifth port, so that the third port and the fourth port in the second relief valve are connected, thereby realizing the pilot control oil of the pilot control valve to be discharged from the third port or the fourth port. When the pilot control oil in the pilot control valve is discharged, the pilot control oil in the main control valve is reduced, thereby reducing the valve core movement speed of the main control valve, and finally reducing the pressure oil input rate obtained by the lifting cylinder, completing the buffering of the pressure action process.

[0030] The second port is connected to the fourth port provided in the second relief valve; when the first port and the second port are connected, after the second relief valve is opened, the pilot control oil flows from the third port to the fourth port, and the pilot control oil in the fourth port is gradually balanced with the pilot control oil in the second port, thereby stopping the buffer discharge.

[0031] The lifting cylinder is provided with a proximity switch 6 for controlling the conduction between the first port and the second port. The hydraulic action state of the lifting cylinder 5 is obtained through the proximity switch 6. The proximity switch detects the distance between the lifting cylinder and the fixed reference object. When the lifting cylinder moves to a position relative to the fixed reference object, the proximity switch sends a signal. The proximity switch sends the signal to the electric proportional relief valve. The coil in the electric proportional relief valve is energized after receiving the signal, so that the first port and the second port are connected.

[0032] When the first port and the second port are connected, the fifth port releases pressure to connect the third port and the fourth port. Under normal conditions, the pressure between the third port and the fourth port of the second relief valve is balanced. When the pressure is released, the valve core of the second relief valve is shifted by the electromagnetic relief valve, so that the third port and the fourth port of the second relief valve can respectively release pressure and buffer different working states of the pilot control valve, so that in addition to the threshold buffering, the hydraulic process can be buffered to any degree at any time.

[0033] In other embodiments, the proximity switch of the present invention comprises an upper proximity switch and a lower proximity switch arranged in sequence, and the upper proximity switch and the lower proximity switch respectively detect positions corresponding to different working states of the lifting cylinder. The upper proximity switch detects the position during lifting, and the lower proximity switch detects the position during lowering. When the upper proximity switch or the lower proximity switch detects the respective corresponding positions, they respectively send out respective signals.

[0034] The upper proximity switch sends a first proximity signal; the first proximity signal is sent to the electric proportional relief valve. After receiving the first proximity signal, the coil of the electric proportional relief valve is energized, so that the first port and the second port are connected. When the first proximity signal is received, it means that the hydraulic process corresponding to the lifting cylinder has reached the limit position.

[0035] The lower proximity switch sends a second proximity signal. The upper proximity switch and the lower proximity switch send buffering control at different positions.

[0036] In other embodiments, the main control valve of the present scheme is connected to an overflow control unit, through which the pilot control oil in the main control valve is overflow controlled, and the overflow control is used to achieve release buffering of the pilot control oil during the hydraulic control process.

[0037] The overflow control unit controls the pilot control oil flowing to the valve core inside the main control valve; when discharge buffering is required, the overflow control unit reduces the input of the pilot control oil, and when normal hydraulic action is performed, the input and regulation of the pilot control oil of the main control valve is achieved through the overflow control unit.

[0038] The overflow control unit controls the release of the pilot control oil according to the signal of the proximity switch. The overflow control unit is used to control the valve core position of the main control valve through the pilot control oil.

[0039] In other embodiments, the pilot control valve of the present solution is located in the overflow control part, and the overflow control part controls the pilot control oil in the main control valve through the pilot control valve to achieve normal hydraulic action. The pilot control valve includes a first pilot control valve and a second pilot control valve respectively connected to the main control valve, and the two pilot control valves respectively control the pilot control oil for different hydraulic action processes.

[0040] When in use, the first pilot control valve and the second pilot control valve respectively control the pilot control oil to enter the valve core of the main control valve from different directions, and the first pilot control valve and the second pilot control valve respectively realize the displacement of the valve core of the main control valve in different directions, thereby performing different working modes.

[0041] In other embodiments, the overflow control unit described in this solution includes an overflow passage connected to the main control valve, the overflow passage is connected to the second overflow valve, and the overflow passage is connected to the first pilot control valve and the second pilot control valve respectively. The pilot control oil in the hydraulic circuit is discharged through the overflow passage, thereby adjusting the valve core position of the main control valve.

[0042] In other embodiments, the second overflow valve of the present solution conducts different overflow paths according to different signals of the proximity switch; the proximity switch sends different signals for different positions. Wherein, when there are multiple proximity switches, the multiple proximity switches send different signals according to their respective position thresholds. And each proximity switch is directly connected to the electric proportional overflow valve. When the proximity switch sends a signal, the electric proportional overflow valve is turned on, thereby connecting different circuits of the second overflow valve, thereby realizing the discharge of different ports of the overflow path.

[0043] When the overflow passage is connected, the pilot control oil in the pilot control valve is released, so that different releases can be performed for different hydraulic processes. When the overflow passage is released through different ports, the pilot control oil corresponding to the different ports of the pilot control valve is reduced, so that buffering can be achieved under different hydraulic actions.

[0044] In other embodiments, the scheme includes a pilot oil source valve 7, which is connected to the pilot control valve 3 and the second relief valve 2 respectively, and provides pilot control oil through the pilot oil source valve. The pilot oil source valve simultaneously inputs the pilot control oil into the second relief valve and the pilot control valve, and is cut off at the second relief valve, but continues to input the pilot control valve, so as to complete all the pilot control oil required for the hydraulic action.

[0045] The pilot oil source valve outputs the pilot control oil, and the pilot control oil is obtained through the pilot oil source valve.

[0046] In other embodiments, the main control valve of this solution is connected to a hydraulic oil unit, and the hydraulic oil unit inputs hydraulic oil to the valve core inside the main control valve; the hydraulic oil unit inputs hydraulic oil to the main control valve and inputs pilot control oil to the overflow control unit, providing oil for the hydraulic action process.

[0047] The main control valve is provided with a PD port connected to a hydraulic oil unit, and the hydraulic oil unit inputs pressure oil into the main control valve from the PD port, and delivers hydraulic oil to the valve core of the main control valve through the hydraulic oil unit.

[0048] In other embodiments, the hydraulic oil unit of this solution includes an oil pump 8 for inputting hydraulic oil to the main control valve, and the oil pump 8 is connected to a hydraulic oil tank 9, and the hydraulic oil tank 9 stores pressurized oil. The hydraulic oil is obtained through the oil pump.

[0049] In other embodiments, the lifting cylinder of the present invention is connected to a mast, and the mast is rigidly connected to the piston rod inside the lifting cylinder; relying on the mast to lift to the top buffer, the safety and comfort during work are improved, the service life of the cylinder is extended, and the hydraulic buffering during the operation of the forklift is realized. The proximity switch detects the position of the mast and sends a signal when the threshold is reached.

[0050] In other embodiments, the present solution includes an electric proportional relief valve 1, the electric proportional relief valve 1 is connected to a second relief valve 2, the electric proportional relief valve 1 and the second relief valve 2 are connected to a pilot control valve 3, the pilot control valve 3 is connected to a main control valve 4, and the main control valve 4 is connected to a lifting cylinder 5. The lifting cylinder is provided with an upper proximity switch and a lower proximity switch. When in use, the oil pump draws oil from the hydraulic oil tank, so that the pressure oil is pumped into the system by the oil pump. Part of the pressure oil reaches the PD port of the main control valve, and the other part of the pressure oil enters from the P1 port of the pilot oil source valve, and enters the accumulator after being reduced in pressure. Then the pilot control oil flows out from the V2 port of the pilot oil source valve, and part of it reaches the third port of the second relief valve, and the other part reaches the PK port of the pilot control valve.

[0051] In other embodiments, the first port of the electric proportional relief valve is connected to the fifth port of the second relief valve. Since the coil of the electric proportional relief valve is not energized, the electric proportional relief valve remains in a closed state. The relief valve also remains in a closed state under the action of the pilot oil pressure on both sides and the spring, so that the pilot control oil is cut off at the third port of the second relief valve.

[0052] When the pilot control valve does not move, the pilot control oil is cut off at its PK port. At this time, the main control valve and the lifting cylinder do not move.

[0053] When the pilot control valve does not move, the pilot control oil is cut off at its PK port. At this time, the main control valve and the lifting cylinder do not move.

[0054] When the C1 port of the pilot control valve is activated, its internal oil circuit is connected. At this time, the pilot control oil flows in from the PK port, then flows out from the C1 port of the pilot control valve after passing through the pilot control valve, and reaches the A1 port of the main control valve. The valve core of the main control valve changes to the left position. The pressure oil at the PD port of the pilot control valve enters the main control valve, flows out from the A1 port of the main control valve after passing through the valve core of the main control valve, reaches the rodless chamber of the lifting cylinder, and extends the piston rod to lift the mast. When the mast is lifted close to the top, that is, when the mast is about to complete the lifting stroke, the upper proximity switch detects the signal of the mast approaching, so that the electric proportional relief valve gets a high level, the coil is energized, and the electric proportional relief valve opens at this time, so that the first port of the electric proportional relief valve is connected to the second port. The control pressure oil at the fifth port of the second relief valve is unloaded through the relief valve. The second relief valve is opened, and the pilot control oil in the pipeline is unloaded through the second relief valve. The valve core of the main control valve 4 gradually changes to the middle position, and the extension of the piston rod in the lifting cylinder 5 gradually stops, so that the lifting of the mast stops.

[0055] When the C2 port of the pilot control valve 3 is activated, its internal oil circuit is connected, the pilot control oil flows in from the PK port, flows out through the C2 port of the pilot control valve 3, and reaches the B1 port of the main control valve 4. Then the valve core of the main control valve 4 moves to the right position, the pressure oil at the PD port enters the main control valve 4, is cut off at the valve core, and the system pressure is controlled by the relief valve in the main control valve 4. The pressure oil in the rodless chamber of the lifting cylinder 5 returns to the main control valve 4 through the A1 port, and returns oil from the TD port through the valve core, so that the piston rod of the lifting cylinder 5 retracts and the mast descends. When the mast descends to near the bottom, the lower proximity switch detects a signal, so that the electric proportional relief valve 1 gets a high level, and the coil is energized. At this time, the electric proportional relief valve 1 opens, so that the first port and the second port in the electric proportional relief valve 1 are connected, and the control pressure oil at the fifth port of the second relief valve is unloaded through the second relief valve. The valve core of the main control valve 4 gradually changes to the middle position, and the retraction of the piston rod in the lifting cylinder 5 gradually stops, thereby stopping the descent of the mast.

[0056] These modifications or improvements made on the basis of the present invention without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A forklift lifting buffer hydraulic circuit, characterized in that: include: A main control valve, the main control valve is connected to a lifting cylinder, and the main control valve controls the pressure oil to the lifting cylinder; the main control valve is connected to a pilot control valve, and the pilot control valve controls the pilot control oil; The main control valve is connected to an electric proportional relief valve and a second relief valve which are connected in sequence, the electric proportional relief valve is connected to the lifting cylinder, and the second relief valve is provided with a third port connected to the pilot control valve; The electric proportional relief valve is provided with a first port and a second port, wherein the first port is connected to the fifth port provided on the second relief valve; and the second port is connected to the fourth port provided on the second relief valve; The lifting oil cylinder is provided with a proximity switch for controlling the connection between the first port and the second port. When the first port and the second port are connected, the fifth port releases pressure to connect the third port and the fourth port.

2. A forklift lifting buffer hydraulic circuit according to claim 1, characterized in that: The proximity switch comprises an upper proximity switch and a lower proximity switch which are arranged in sequence. The upper proximity switch sends a first proximity signal; and the lower proximity switch sends a second proximity signal.

3. A forklift lifting buffer hydraulic circuit according to claim 1 or 2, characterized in that: The main control valve is connected to an overflow control unit, and the overflow control unit controls the pilot control oil flowing to the valve core inside the main control valve; the overflow control unit controls the discharge of the pilot control oil according to the signal of the proximity switch.

4. A forklift lifting buffer hydraulic circuit according to claim 3, characterized in that: The pilot control valve is located in the overflow control part, and the pilot control valve includes a first pilot control valve and a second pilot control valve respectively connected to the main control valve. The first pilot control valve and the second pilot control valve respectively control the pilot control oil to enter the valve core of the main control valve from different directions.

5. The forklift lifting buffer hydraulic circuit according to claim 3, characterized in that: The overflow control unit includes an overflow passage connected to the main control valve, the overflow passage is connected to the second overflow valve, and the overflow passage is connected to the first pilot control valve and the second pilot control valve respectively.

6. A forklift lifting buffer hydraulic circuit according to claim 5, characterized in that: The second overflow valve conducts different overflow paths according to different signals of the proximity switch; when the overflow path is conducted, the pilot control oil in the pilot control valve is discharged.

7. A forklift lifting buffer hydraulic circuit according to claim 1 or 2, characterized in that: It comprises a pilot oil source valve, which is respectively connected to the pilot control valve and the second relief valve, and outputs pilot control oil.

8. The forklift lifting buffer hydraulic circuit according to claim 1, characterized in that: The main control valve is connected to a hydraulic oil unit, which inputs hydraulic oil to the valve core inside the main control valve; the main control valve is provided with a PD port connected to the hydraulic oil unit, and the hydraulic oil unit inputs pressure oil from the PD port to the main control valve.

9. A forklift lifting buffer hydraulic circuit according to claim 8, characterized in that: The hydraulic oil unit comprises an oil pump for inputting hydraulic oil to the main control valve. The oil pump is connected to a hydraulic oil tank, and the hydraulic oil tank stores pressurized oil.

10. A forklift lifting buffer hydraulic circuit according to claim 1 or 2, characterized in that: The lifting cylinder is connected with a gantry, and the gantry is rigidly connected to the piston rod inside the lifting cylinder; the proximity switch detects the position of the gantry and sends a signal when a threshold value is reached.

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