Forklift loader and brake hydraulic control system thereof

Abstract

The utility model discloses a forklift loader and a brake hydraulic control system thereof. The system comprises a hydraulic oil tank, a load sensitive mechanism, a power source, an LS type prefill valve, a first energy accumulator, a second energy accumulator and a switch control valve. An oil inlet of the load-sensitive mechanism is communicated with the hydraulic oil tank, and a pressure oil port of the load-sensitive mechanism is communicated with an oil inlet of the LS type prefill valve 5; a first working oil port of the LS type prefill valve is communicated with the first energy accumulator and a first oil inlet of the brake valve, and a second working oil port of the LS type prefill valve is communicated with the second energy accumulator and a second oil inlet of the brake valve; a feedback oil port of the LS type prefill valve is communicated with a feedback oil port of the load sensitive mechanism through the switch control valve; and an oil return port of the LS type prefill valve and an oil return port of the switch control valve are communicated with the hydraulic oil tank. According to the utility model, the problem that the engine is difficult to start and even cannot be started due to large starting torque in the restarting process after the engine flames out is solved.

Description

Technical Field

[0001] The utility model belongs to the technical field of hydraulic control, and particularly relates to a forklift truck and its braking hydraulic control system. Background Art

[0002] In the existing hydraulic system of a forklift truck, the braking system is provided with a braking pressure oil source by hydraulic pressure, and the braking system should meet the following two requirements stipulated by the standard:

[0003] (1) When the vehicle needs to brake during driving, the braking system should be able to provide the braking pressure required for braking;

[0004] (2) When the engine of the vehicle stalls abnormally during driving, the braking system can still provide sufficient braking pressure to stop the vehicle.

[0005] The hydraulic system of the braking part consists of an oil supply pump, a filling valve, a brake accumulator, a brake valve, a hydraulic oil tank, hydraulic oil, oil pipes and a filter. When the oil supply pump is a load-sensitive pump, the filling valve should adopt an LS (Load Senser) type filling valve. The P port (i.e., the pressure oil port or the oil inlet port) of the load-sensitive pump is communicated with the P port of the LS type filling valve. The A1 port and A2 port of the LS type filling valve are communicated with the brake accumulator and the P port of the brake valve at the same time. The LS port (i.e., the load feedback oil port) of the LS type filling valve is communicated with the LS port of the load-sensitive pump. The V1 port (i.e., the oil inlet port) of the brake valve is communicated with the oil inlet port of the brake on the axle. When stepping on the brake pedal of the brake valve, the high-pressure oil stored in the brake accumulator enters the brake on the axle through the brake valve, so that the vehicle decelerates and stops. At this time, the pressure in the brake accumulator decreases due to release. When it decreases to the lower limit of the set pressure, the filling switch in the LS type filling valve changes direction and opens. The filling port of the LS type filling valve is communicated with the LS port of the load-sensitive pump, so that the displacement of the load-sensitive pump is increased, and the output pressure oil fills the brake accumulator; when the oil pressure in the brake accumulator reaches the upper limit of the set value, the filling switch in the LS type filling valve changes direction and closes, and the filling port of the LS type filling valve is disconnected from the LS port of the load-sensitive pump, so that the displacement of the load-sensitive pump is decreased.

[0006] When the engine stalls, if the brake pedal is depressed or after a long time of placement (the pressure of the brake accumulator decreases due to internal leakage in the system), the braking pressure is released either quickly or slowly, resulting in a decrease in the pressure in the brake accumulator. As a result, the filling switch in the LS type filling valve changes direction and opens, causing the filling port of the LS type filling valve to communicate with the LS port of the load sensing pump, and the pressurized oil is transmitted to the LS port of the load sensing pump. At this time, since the vehicle is in a stalled state and the load sensing pump cannot supply pressurized oil to the system, the pressure in the brake accumulator cannot reach the upper limit value again. Therefore, the filling switch in the LS type filling valve cannot change direction and close, and thus the pressure at the LS port of the load sensing pump cannot be released, and this part of the pressure will always exist in the hydraulic pipeline. When the engine is restarted in this state, due to the pressure existing at the LS port of the load sensing pump and the one-way connection between the P port and the LS port of the load sensing pump, the load sensing pump cannot quickly switch the pump displacement to the minimum displacement state to start the engine at a lower torque. Instead, it is necessary to first fill the brake accumulator with pressurized oil until the filling closing pressure is reached, and then close the filling switch in the LS type filling valve (operating in the left position). At this time, the LS port of the load sensing pump communicates with the hydraulic oil tank, and the LS pressure rapidly drops to almost zero. The LS differential pressure control valve in the load sensing pump switches to the left position for operation, the displacement of the load sensing pump is adjusted to the minimum state, and the pressure at the P port of the load sensing pump decreases, and the system only maintains the internal leakage state. During this starting process, the engine is in a state of relatively large torque both at the moment of starting and for a short period of time after starting, and the required starting torque is relatively large, which may cause difficulties in starting the engine or even prevent it from starting. Summary of the Utility Model

[0007] The purpose of the present utility model is to provide a forklift truck and its braking hydraulic control system to solve the problem that during the restart process after the engine stalls, the required starting torque is relatively large, resulting in difficulties in starting the engine or even preventing it from starting.

[0008] The present utility model solves the above technical problems through the following technical solutions: A braking hydraulic control system includes a hydraulic oil tank, a load sensing mechanism, a power source, an LS type filling valve, a first accumulator, and a second accumulator; the load sensing mechanism is driven by the power source, and the oil inlet of the load sensing mechanism communicates with the hydraulic oil tank, and the pressurized oil port of the load sensing mechanism communicates with the oil inlet of the LS type filling valve; the first working oil port of the LS type filling valve communicates with the first accumulator and the first oil inlet of the brake valve, and the second working oil port of the LS type filling valve communicates with the second accumulator and the second oil inlet of the brake valve;

[0009] The system further includes a switch control valve; the feedback oil port of the LS type filling valve communicates with the feedback oil port of the load sensing mechanism through the switch control valve, and the switch control valve communicates with the hydraulic oil tank.

[0010] Further, the load sensing mechanism includes a variable pump, a first differential pressure control valve, a second differential pressure control valve, and a variable oil cylinder. The variable pump is driven by a power source. The inlet port of the variable pump serves as the inlet port of the load sensing mechanism and is connected to the hydraulic oil tank. The outlet port of the variable pump serves as the pressure oil port of the load sensing mechanism, and the outlet port of the variable pump is connected to the first port of the first differential pressure control valve and the second differential pressure control valve. The fourth port of the first differential pressure control valve is connected to the second port of the second differential pressure control valve. The third port of the first differential pressure control valve serves as the feedback oil port of the load sensing mechanism and is connected to the switch control valve. The second port and the fourth port of the first differential pressure control valve, and the third port and the fourth port of the second differential pressure control valve are connected to the hydraulic oil tank. The fourth port of the second differential pressure control valve is further connected to the variable oil cylinder, and the variable oil cylinder is connected to the variable pump.

[0011] Further, the LS type filling valve includes a first hydraulic control directional valve, a second hydraulic control directional valve, and a third hydraulic control directional valve. The pressure oil port of the load sensing mechanism is connected to the control port of the first hydraulic control directional valve, and the inlet ports of the second hydraulic control directional valve and the third hydraulic control directional valve. The outlet port of the first hydraulic control directional valve serves as the feedback oil port of the LS type filling valve and is connected to the switch control valve. The outlet port of the second hydraulic control directional valve serves as the first working oil port, and the outlet port of the third hydraulic control directional valve serves as the second working oil port.

[0012] Further, the LS type filling valve further includes a check valve. The pressure oil port of the load sensing mechanism is connected to the control port of the first hydraulic control directional valve, and the inlet ports of the second hydraulic control directional valve and the third hydraulic control directional valve through the check valve.

[0013] Further, the first hydraulic control directional valve is a two-position three-way hydraulic control directional valve, and the second hydraulic control directional valve and the third hydraulic control directional valve are two-position two-way hydraulic control directional valves.

[0014] Further, the switch control valve is an electromagnetic valve. When the power source is not started or abnormally shuts down, the electromagnetic valve is in a de-energized state, and the feedback oil port of the LS type filling valve is disconnected from the feedback oil port of the load sensing mechanism. When the power source is fully started, the electromagnetic valve is in an energized state, and the feedback oil port of the LS type filling valve is connected to the feedback oil port of the load sensing mechanism.

[0015] Further, the power source is an engine or a drive motor.

[0016] Based on the same concept, the present invention further provides a forklift truck, which includes the braking hydraulic control system as described above.

[0017] Beneficial effects

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] A switching control valve is additionally provided on the pipeline between the feedback oil port of the LS type liquid filling valve and the feedback oil port of the load sensing mechanism. When the engine shuts down, the switching control valve is closed, so that the communication pressure between the feedback oil port of the load sensing mechanism and the hydraulic oil tank is almost zero, and the feedback oil port of the LS type liquid filling valve is disconnected. After stepping on the brake pedal or after a long time of placement, due to the commutation of the liquid filling switch in the LS type liquid filling valve, it is opened, and the pressure oil coming out of the first accumulator and the second accumulator cannot be transmitted to the feedback oil port of the load sensing mechanism; after the engine is fully started, the switching control valve is opened, and the feedback oil port of the LS type liquid filling valve is communicated with the feedback oil port of the load sensing mechanism. At this time, the pressure oil can be transmitted to the feedback oil port of the load sensing mechanism, and the load sensing mechanism adjusts the large displacement to fill the first accumulator and the second accumulator with liquid; after the liquid filling is completed, the liquid filling switch in the LS type liquid filling valve commutes and closes, the feedback oil port of the load sensing mechanism is communicated with the hydraulic oil tank, and the load feedback pressure rapidly drops to almost zero. The differential pressure control valve in the load sensing mechanism switches to the left position to work, and the displacement of the load sensing mechanism is adjusted to the minimum state.

[0020] The braking hydraulic system provided by the present utility model adopts a switching control valve, which while meeting the two requirements specified by the standard for the braking system, avoids the problem that the engine is difficult to start or even cannot start due to the large starting torque required during the process of restarting after the engine shuts down. Brief Description of the Drawings

[0021] In order to more clearly illustrate the technical solution of the present utility model, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only one embodiment of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is the schematic diagram of the braking hydraulic control system in the embodiment of the present utility model.

[0023] Description of the reference numerals: 1 - hydraulic oil tank, 2 - load sensing mechanism, 21 - first differential pressure control valve, 22 - second differential pressure control valve, 23 - variable pump, 24 - variable oil cylinder, 3 - power source, 4 - solenoid valve, 5 - LS type liquid filling valve, 51 - third hydraulic control reversing valve, 52 - second hydraulic control reversing valve, 53 - first hydraulic control reversing valve, 6 - second accumulator, 7 - first accumulator, 8 - brake valve, 81 - brake pedal, 9 - front axle brake, 10 - rear axle brake. Detailed Embodiment

[0024] The following clearly and completely describes the technical solutions in the embodiments of the present utility model with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part rather than all of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts fall within the scope of protection of the present utility model.

[0025] As Figure 1 shown, a brake hydraulic control system provided by an embodiment of the present utility model includes a hydraulic oil tank 1, a load sensing mechanism 2, a power source 3, an LS type filling valve 5, a first accumulator 7, a second accumulator 6, and a switching control valve; the load sensing mechanism 2 is driven by the power source 3, and the oil inlet (i.e., the S port) of the load sensing mechanism 2 is communicated with the hydraulic oil tank 1, and the pressure oil port (i.e., the P port) of the load sensing mechanism 2 is communicated with the oil inlet (i.e., the P port) of the LS type filling valve 5; the first working oil port (i.e., the A1 port) of the LS type filling valve 5 is communicated with the first accumulator 7 and the first oil inlet (i.e., the P1 port) of the brake valve 8, and the second working oil port (i.e., the A2 port) of the LS type filling valve 5 is communicated with the second accumulator 6 and the second oil inlet (i.e., the P2 port) of the brake valve 8; the feedback oil port (i.e., the LS port) of the LS type filling valve 5 is communicated with the feedback oil port (i.e., the PL port) of the load sensing mechanism 2 through the switching control valve. The oil return port (i.e., the T port) of the LS type filling valve 5 and the oil return port of the switching control valve are communicated with the hydraulic oil tank 1.

[0026] The system of the present utility model supplies oil to the LS type filling valve 5 by a load sensing mechanism 2. The feedback oil port of the LS type filling valve 5 is communicated with the first oil port of the switching control valve. The first working oil port of the LS type filling valve 5 is communicated with the first accumulator 7 and the first oil inlet of the brake valve 8 at the same time. The second working oil port of the LS type filling valve 5 is communicated with the second accumulator 6 and the second oil inlet of the brake valve 8 at the same time. The first working oil port (i.e., the A1 port) of the brake valve 8 is communicated with the oil port of the rear axle brake 10, and the second working oil port (i.e., the A2 port) of the brake valve 8 is communicated with the oil port of the front axle brake 9.

[0027] In the specific embodiments of the present utility model, the load sensing mechanism 2 includes a variable pump 23, a first differential pressure control valve 21, a second differential pressure control valve 22, and a variable oil cylinder 24. The variable pump 23 is driven by a power source 3. The inlet port (i.e., the S port) of the variable pump 23 serves as the inlet port of the load sensing mechanism 2 and is connected to the hydraulic oil tank 1. The outlet port (i.e., the P port) of the variable pump 23 serves as the pressure oil port of the load sensing mechanism 2, and the outlet port of the variable pump 23 is connected to the first port of the first differential pressure control valve 21 and the second differential pressure control valve 22. The fourth port of the first differential pressure control valve 21 is connected to the second port of the second differential pressure control valve 22. The third port of the first differential pressure control valve 21 serves as the feedback oil port (i.e., the PL port) of the load sensing mechanism 2 and is connected to the switching control valve. The second and fourth ports of the first differential pressure control valve 21 and the third and fourth ports of the second differential pressure control valve 22 are connected to the hydraulic oil tank 1. The fourth port of the second differential pressure control valve 22 is further connected to the variable oil cylinder 24, and the variable oil cylinder 24 is connected to the variable pump 23.

[0028] The load feedback pressure is fed back to the control port (i.e., the third port of the first differential pressure control valve 21) of the first differential pressure control valve 21 through the feedback oil path. Through the first differential pressure control valve 21 and the second differential pressure control valve 22, the difference between the outlet pressure of the variable pump 23 and the load feedback pressure is variable. In this embodiment, the first differential pressure control valve 21 and the second differential pressure control valve 22 can adopt proportional valves. When the spool is in the left position, the high-pressure oil at the outlet of the variable pump 23 enters the variable oil cylinder 24, and the displacement of the variable pump 23 becomes smaller. When the spool is in the right position, the pressure oil of the variable oil cylinder 24 returns, and the displacement of the variable pump 23 becomes larger. When the spool is stable in the middle position, the variable pump 23 will be stable at a certain displacement.

[0029] In the specific embodiments of the present utility model, the LS type filling valve 5 includes a first hydraulic control reversing valve 53, a second hydraulic control reversing valve 52, and a third hydraulic control reversing valve 51. The pressure oil port of the load sensing mechanism 2 (i.e., the outlet port of the variable pump 23) is connected to the control port of the first hydraulic control reversing valve 53, the inlet ports of the second hydraulic control reversing valve 52 and the third hydraulic control reversing valve 51. The outlet port of the first hydraulic control reversing valve 53 serves as the feedback oil port of the LS type filling valve 5 and is connected to the switching control valve. The outlet port of the second hydraulic control reversing valve 52 serves as the first working oil port (i.e., the A1 port) of the LS type filling valve 5, and the outlet port of the third hydraulic control reversing valve 51 serves as the second working oil port (i.e., the A2 port) of the LS type filling valve 5.

[0030] In the specific embodiments of the present utility model, the LS type filling valve 5 further includes a check valve. The pressure oil port of the load sensing mechanism 2 is connected to the control port of the first hydraulic control reversing valve 53, the inlet ports of the second hydraulic control reversing valve 52 and the third hydraulic control reversing valve 51 through the check valve.

[0031] In this embodiment, the first hydraulic control reversing valve 53 is a two-position three-way hydraulic control reversing valve, and the second hydraulic control reversing valve 52 and the third hydraulic control reversing valve 51 are two-position two-way hydraulic control reversing valves. Let the pressure when the first hydraulic control reversing valve 53 is fully in the right position be the filling opening pressure, and the pressure when the first hydraulic control reversing valve 53 is fully in the left position be the filling closing pressure.

[0032] The set pressure of the right spring of the first hydraulic control reversing valve 53 in the LS type filling valve 5 is the filling opening pressure, and the pressure when the left oil pressure fully pushes the first hydraulic control reversing valve 53 to the left position is the filling closing pressure. Generally, the opening pressure is about 3 MPa lower than the closing pressure. When the sum of the acting force generated by the right spring force of the second hydraulic control reversing valve 52 or the third hydraulic control reversing valve 51 in the LS type filling valve 5 and the pressure of the corresponding accumulator (i.e., the first accumulator 7 or the second accumulator 6) is lower than the filling opening pressure, the second hydraulic control reversing valve 52 or the third hydraulic control reversing valve 51 changes its position, connecting the corresponding accumulator to the oil inlet of the LS type filling valve 5; when the sum of the acting force generated by the right spring force of the second hydraulic control reversing valve 52 or the third hydraulic control reversing valve 51 in the LS type filling valve 5 and the pressure of the corresponding accumulator is higher than the filling closing pressure, the second hydraulic control reversing valve 52 or the third hydraulic control reversing valve 51 is in the right position.

[0033] In the starting state, when the pressure in the first accumulator 7 or the second accumulator 6 drops to the filling opening pressure, the second hydraulic control reversing valve 52 or the third hydraulic control reversing valve 51 changes its position and is in the left position, connecting the first accumulator 7 and the second accumulator 6 to the oil inlet of the LS type filling valve 5 and also to the left end of the first hydraulic control reversing valve 53. Due to the existence of the right spring force, the first hydraulic control reversing valve 53 of the LS type filling valve 5 is pushed to the right position. The feedback oil port of the LS type filling valve 5 transmits the pressure in the first accumulator 7 and the second accumulator 6 to the right side of the first differential pressure control valve 21 of the load sensing mechanism 2, increasing the displacement of the variable pump 23 and the outlet flow rate to fill the first accumulator 7 and the second accumulator 6.

[0034] In the starting state, when the pressure in the first accumulator 7 and the second accumulator 6 reaches the filling closing pressure, the first hydraulic control reversing valve 53 is pushed to the left position, and the load feedback oil circuit of the load sensing mechanism 2 is connected to the T port and rapidly drops to almost zero. The displacement of the variable pump 23 decreases, and the system maintains the internal leakage flow rate.

[0035] In the specific embodiments of the present utility model, the switching control valve is a two-position three-way solenoid valve 4 or a hydraulic control reversing valve with the same function. When the power source 3 is not started or abnormally shuts down, the two-position three-way solenoid valve 4 is de-energized and in the left position. The feedback oil port of the LS type filling valve 5 is disconnected from the feedback oil port of the load sensing mechanism 2, and the feedback oil port of the load sensing mechanism 2 is connected to the hydraulic oil tank 1 through the two-position three-way solenoid valve 4. When the power source 3 is fully started, the two-position three-way solenoid valve 4 is energized and in the right position, and the feedback oil port of the LS type filling valve 5 is connected to the feedback oil port of the load sensing mechanism 2.

[0036] When the power source 3 is not started or abnormally shuts down, when the brake pedal 81 is stepped on or left for a long time, the pressure stored in the first accumulator 7 and the second accumulator 6 decreases. When the pressure decreases to the filling opening pressure, the second hydraulic control reversing valve 52 and the third hydraulic control reversing valve 51 change their positions and are in the left position, and the first hydraulic control reversing valve 53 changes its position and is in the left position. The first accumulator 7 and the second accumulator 6 are connected to the feedback oil port of the LS type filling valve 5, but the pressure oil cannot be transmitted to the feedback oil port of the load sensing mechanism 2.

[0037] When starting the power source 3, since the two-position three-way solenoid valve 4 is energized after the power source 3 is fully started, during the starting process, the feedback oil port of the load sensing mechanism 2 is still connected to the hydraulic oil tank 1 through the two-position three-way solenoid valve 4. When the power source 3 is started, the load sensing mechanism 2 only needs to raise the outlet pressure to overcome the spring force on the right side of the first differential pressure control valve 21, and then the first differential pressure control valve 21 can be pushed to the left position to work, thereby adjusting the displacement of the variable pump 23 to the minimum state. The spring setting pressure on the right side of the first differential pressure control valve 21 is much lower than the filling closing pressure of the LS type filling valve 5. Generally, the filling closing pressure of the LS type filling valve 5 is 7 times the spring setting pressure on the right side of the first differential pressure control valve 21. Therefore, the starting torque of the power source 3 is reduced by 7 times. This avoids the problem that the engine is difficult to start or even cannot start due to the large required starting torque during the process of restarting after the engine shuts down.

[0038] In the specific embodiments of the present utility model, the power source 3 is an engine or a drive motor.

[0039] The utility model can greatly reduce the starting torque of the power source 3 (such as an engine), and will not have problems of inability to start or difficult starting due to excessive starting torque. When the vehicle is turned off, the pressure oil in the first accumulator 7 and the second accumulator 6 will not be led to the feedback oil port of the load sensing mechanism 2 due to the driver stepping on the brake pedal 81 or long-term placement. When the power source 3 (such as an engine) stalls abnormally, the pressure in the first accumulator 7 and the second accumulator 6 can be fully used for the braking system, and other systems will not consume the pressure in the first accumulator 7 and the second accumulator 6. When the power source 3 (such as an engine) stalls abnormally, when stepping on the brake pedal 81, there will be no pressure buildup in the pipeline connecting the load sensing mechanism 2, so when the load sensing mechanism 2 needs to be repaired, the braking system will not fail. When the power source 3 (such as an engine) is in the off state, the leakage of other LS circuits in the system will not affect the braking system.

[0040] The utility model avoids the increase in the starting torque of the engine due to long-term placement or abnormal operation, can also provide the required pressure for the braking system after the engine is fully started, and can ensure that the required pressure is provided for the braking system to stop the vehicle when the engine stalls abnormally. After the engine is normally started, the feedback oil port of the load sensing mechanism 2 is communicated with the feedback oil port of the LS type filling valve 5. When the engine is in the off state, the feedback oil port of the load sensing mechanism 2 is communicated with the hydraulic oil tank 1. The two-position three-way solenoid valve 4 is energized when the engine speed reaches the idle speed and de-energized when the engine speed is zero.

[0041] The above-disclosed are only the specific embodiments of the utility model, but the protection scope of the utility model is not limited thereto. Any person skilled in the art within the technical scope disclosed by the utility model can easily think of changes or modifications, which should all be covered within the protection scope of the utility model.

Claims

1. A brake hydraulic control system, comprising a hydraulic oil tank, a load sensing mechanism, a power source, an LS type filling valve, a first accumulator and a second accumulator; the load sensing mechanism is driven by the power source, and the oil inlet of the load sensing mechanism is connected to the hydraulic oil tank, and the pressure oil port of the load sensing mechanism is connected to the oil inlet of the LS type filling valve; the first working oil port of the LS type filling valve is connected to the first accumulator and the first oil inlet of the brake valve, and the second working oil port of the LS type filling valve is connected to the second accumulator and the second oil inlet of the brake valve; characterized in that: The system further comprises a switch control valve; the feedback oil port of the LS type filling valve is connected to the feedback oil port of the load sensing mechanism through the switch control valve, and the switch control valve is connected to the hydraulic oil tank.

2. The brake hydraulic pressure control system according to claim 1, characterized in that: The load-sensitive mechanism includes a variable pump, a first differential pressure control valve, a second differential pressure control valve and a variable oil cylinder. The variable pump is driven by a power source. The oil inlet of the variable pump is connected to the hydraulic oil tank as the oil inlet of the load-sensitive mechanism. The oil outlet of the variable pump is used as the pressure oil port of the load-sensitive mechanism, and the oil outlet of the variable pump is connected to the first ports of the first differential pressure control valve and the second differential pressure control valve; the fourth port of the first differential pressure control valve is connected to the second port of the second differential pressure control valve, the third port of the first differential pressure control valve is connected to the switch control valve as the feedback oil port of the load-sensitive mechanism, the second port and the fourth port of the first differential pressure control valve, the third port and the fourth port of the second differential pressure control valve are connected to the hydraulic oil tank; the fourth port of the second differential pressure control valve is also connected to the variable oil cylinder, and the variable oil cylinder is connected to the variable pump.

3. The brake hydraulic pressure control system according to claim 1, characterized in that: The LS type filling valve includes a first hydraulically controlled reversing valve, a second hydraulically controlled reversing valve and a third hydraulically controlled reversing valve; the pressure oil port of the load sensitive mechanism is connected with the control port of the first hydraulically controlled reversing valve, the oil inlet of the second hydraulically controlled reversing valve and the third hydraulically controlled reversing valve, the oil outlet of the first hydraulically controlled reversing valve is connected with the switch control valve as the feedback oil port of the LS type filling valve, the oil outlet of the second hydraulically controlled reversing valve is used as the first working oil port, and the oil outlet of the third hydraulically controlled reversing valve is used as the second working oil port.

4. The brake hydraulic pressure control system according to claim 3, characterized in that: The LS type filling valve also includes a one-way valve, and the pressure oil port of the load sensitive mechanism is connected to the control port of the first hydraulically controlled reversing valve, the second hydraulically controlled reversing valve and the oil inlet of the third hydraulically controlled reversing valve through the one-way valve.

5. The brake hydraulic pressure control system according to claim 3, characterized in that: The first hydraulically controlled reversing valve is a two-position three-way hydraulically controlled reversing valve, and the second hydraulically controlled reversing valve and the third hydraulically controlled reversing valve are two-position two-way hydraulically controlled reversing valves.

6. The brake hydraulic pressure control system according to claim 1, characterized in that: The switch control valve is a solenoid valve; when the power source is not started or is abnormally shut down, the solenoid valve is in a power-off state, and the feedback oil port of the LS type filling valve is disconnected from the feedback oil port of the load sensing mechanism; when the power source is fully started, the solenoid valve is in a power-on state, and the feedback oil port of the LS type filling valve is connected to the feedback oil port of the load sensing mechanism.

7. The brake hydraulic pressure control system according to claim 1, characterized in that: The power source is an engine or a drive motor.

8. A forklift, characterized in that: The forklift truck includes the brake hydraulic control system according to any one of claims 1 to 7.

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