Small loader hydraulic system with integrated pressure maintaining and safety overflow function and working method

Abstract

The present application belongs to the technical field of loader hydraulic system, and particularly relates to a small loader hydraulic system integrated with pressure maintaining and safety overflow functions and a working method thereof. The hydraulic system comprises a boom lifting hydraulic system, a steering hydraulic system, a traveling hydraulic system, a boom stretching and bucket hydraulic system. The working method comprises a working method of the boom lifting hydraulic system, a working method of the steering hydraulic system, a working method of the traveling hydraulic system, and a working method of the boom stretching and bucket hydraulic system. The present application combines emergency unloading function, anti-cavitation function, pressure maintaining function and safety overflow function, determines the actions to be completed by each element of the loader hydraulic system under various working conditions, and establishes each mechanism hydraulic system by applying the characteristics of basic hydraulic elements. Through the design of double overflow safety valve groups and directional valve pressure maintaining in the hydraulic system, the steering valve group and other designs, the loader hydraulic system integrated with multiple functions is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of loader hydraulic system, and particularly relates to a small loader hydraulic system integrating pressure maintaining and safety overflow functions and a working method. BACKGROUND

[0002] As the main driving mode of current loaders, hydraulic driving is of great importance to the optimization and innovation of hydraulic system design. Since various working conditions are very complex in engineering practice, various situations should be fully considered when designing the loader hydraulic system, and extreme and emergency situations should be considered, so that the designed hydraulic system can be better applied in practice.

[0003] Many existing technologies are innovations in mechanical structure or detection of the loader lifting system. For example, Sanqi Group uses a flywheel to drive hydraulic oil to save energy and reduce hydraulic impact; Beiqi Foton Co., Ltd. installs a detection device in front of the hydraulic element to achieve real-time detection and rapid troubleshooting of the hydraulic element; Guangxi Liugong Group designs an auxiliary lifting hydraulic system with an accumulator, which recovers kinetic energy when the boom is lowered to save energy. Most existing patents and researches are mostly innovations in structure or hardware, and even the hydraulic system design rarely considers some extreme situations. SUMMARY

[0004] The application provides a small loader hydraulic system integrating pressure maintaining and safety overflow functions and a working method, which combines emergency unloading function, anti-cavitation function, pressure maintaining function and safety overflow function, determines the actions to be completed by each element of the loader hydraulic system under various working conditions, and establishes each mechanism hydraulic system by using the characteristics of basic hydraulic elements.

[0005] The technical scheme adopted by the application to solve the technical problem is as follows: a small loader hydraulic system integrating pressure maintaining and safety overflow functions, comprising an oil tank, a main oil circuit and a return oil circuit, wherein the main oil circuit is connected with the outlet end of the oil tank, and the return oil circuit is connected with the inlet end of the oil tank; the loader hydraulic system comprises a boom lifting hydraulic system, a steering hydraulic system, a traveling hydraulic system, a boom extension and bucket hydraulic system, wherein:

[0006] The boom lifting hydraulic system, the steering hydraulic system, the traveling hydraulic system and the boom extension and bucket hydraulic system are connected with the main oil circuit at the oil inlet end and connected with the return oil circuit at the oil outlet end.

[0007] A first two-position two-way electromagnetic reversing valve is arranged on the main oil path between the boom lifting hydraulic system and the oil tank, and the communication state of the main oil path between the boom lifting hydraulic system and the oil tank is controlled through the first two-position two-way electromagnetic reversing valve;

[0008] The boom stretching and bucket hydraulic system comprises a boom stretching hydraulic system and a boom bucket hydraulic system, and the boom stretching hydraulic system and the boom bucket hydraulic system are connected with the oil tank through the main oil path;

[0009] A second two-position two-way electromagnetic reversing valve is arranged on the main oil path between the boom stretching hydraulic system and the oil tank and the main oil path between the boom bucket hydraulic system and the oil tank, respectively, the communication state of the main oil path between the boom stretching hydraulic system and the oil tank is controlled through the second two-position two-way electromagnetic reversing valve on the main oil path between the boom stretching hydraulic system and the oil tank, and the communication state of the main oil path between the boom bucket hydraulic system and the oil tank is controlled through the second two-position two-way electromagnetic reversing valve on the main oil path between the boom bucket hydraulic system and the oil tank;

[0010] The boom lifting hydraulic system comprises a boom lifting hydraulic system body and a double safety overflow valve group, the boom lifting hydraulic system body controls the lifting of the boom, the double safety overflow valve group is used for preventing the cylinder from being blocked and stopping the oil path pressure from continuously rising when the boom lifting hydraulic system body operates to the maximum stroke and is still in the working state of continuing lifting, and the double safety overflow valve group is used for protecting the hydraulic elements;

[0011] The steering hydraulic system comprises a full hydraulic steering gear, a steering valve group and a synchronization valve group, and the pressure maintaining function is realized through the cooperation of the full hydraulic steering gear, the steering valve group and the synchronization valve group.

[0012] As a further preferred embodiment of the present application, the boom lifting hydraulic system body comprises a first three-position four-way manual reversing valve, a first single-piston rod hydraulic cylinder, a second single-piston rod hydraulic cylinder, a lifting circuit adjustable throttle valve, a second two-position two-way reversing valve, a lifting circuit check valve, a descending circuit adjustable throttle valve, a first two-position two-way reversing valve and a descending circuit check valve, wherein:

[0013] The P port of the first three-position four-way manual reversing valve is connected with the main oil path, the T port of the first three-position four-way manual reversing valve is connected with the oil return path, the A port of the first three-position four-way manual reversing valve is connected with the left oil cavity of the first single-piston rod hydraulic cylinder and the left oil cavity of the second single-piston rod hydraulic cylinder, and the B port of the first three-position four-way manual reversing valve is connected with the right oil cavity of the first single-piston rod hydraulic cylinder and the right oil cavity of the second single-piston rod hydraulic cylinder;

[0014] A port of the first three-position four-way manual reversing valve is connected with the first single piston rod hydraulic cylinder and the second single piston rod hydraulic cylinder, and a lifting circuit adjustable throttle valve and a second two-position two-way reversing valve are sequentially arranged on a pipeline along an oil path direction;

[0015] The lifting circuit check valve is connected with the lifting circuit adjustable throttle valve in parallel.

[0016] A port of the first three-position four-way manual reversing valve is connected with the first single piston rod hydraulic cylinder and the second single piston rod hydraulic cylinder, and a lifting circuit adjustable throttle valve and a second two-position two-way reversing valve are sequentially arranged on a pipeline along an oil path direction;

[0017] The lifting circuit check valve is connected with the lifting circuit adjustable throttle valve in parallel.

[0018] As a further preferred embodiment of the present application, the double safety overflow valve group comprises a first pipeline, a second overflow valve, a first overflow valve, a second check valve, a first check valve, a descending circuit safety overflow valve, a first two-position two-way electromagnetic reversing valve with lever control, a lifting circuit safety overflow valve, and a second two-position two-way electromagnetic reversing valve with lever control, wherein:

[0019] A pipeline connected with a P port of the second two-position two-way reversing valve is connected with a pipeline connected with a P port of the first two-position two-way reversing valve through the first pipeline;

[0020] The first pipeline is sequentially provided with the second overflow valve and the first overflow valve along the second two-position two-way reversing valve to the first two-position two-way reversing valve, the second overflow valve is connected with the second check valve in parallel, and the first overflow valve is connected with the first check valve in parallel;

[0021] Right side oil chambers of the first single piston rod hydraulic cylinder and the second single piston rod hydraulic cylinder are connected with a P port of the descending circuit safety overflow valve, a T port of the descending circuit safety overflow valve is connected with a return oil path, a Y port of the descending circuit safety overflow valve is connected with a P port of the first two-position two-way electromagnetic reversing valve with lever control, and an A port of the first two-position two-way electromagnetic reversing valve with lever control is connected with the return oil path;

[0022] Left side oil chambers of the first single piston rod hydraulic cylinder and the second single piston rod hydraulic cylinder are connected with a P port of the lifting circuit safety overflow valve, a T port of the lifting circuit safety overflow valve is connected with the return oil path, a Y port of the lifting circuit safety overflow valve is connected with a P port of the second two-position two-way electromagnetic reversing valve with lever control, and an A port of the second two-position two-way electromagnetic reversing valve with lever control is connected with the return oil path.

[0023] As a further preferred embodiment of the present application, the full hydraulic diverter comprises a first three-position four-way electromagnetic valve, a right turning path one-way hydraulic control valve, and a left turning path one-way hydraulic control valve, wherein:

[0024] The A port of the first three-position four-way electromagnetic valve is connected with the A port of the right-turn one-way hydraulic control valve, the B port of the first three-position four-way electromagnetic valve is connected with the A port of the left-turn one-way hydraulic control valve, the P port of the first three-position four-way electromagnetic valve is connected with the steering valve group, and the T port of the first three-position four-way electromagnetic valve is connected with the oil return path;

[0025] The B port of the right-turn one-way hydraulic control valve is connected with the steering valve group, and is connected with the A ports of the first throttle valve and the second throttle valve, and the X port of the right-turn one-way hydraulic control valve is connected with the B port of the first three-position four-way electromagnetic valve;

[0026] The B port of the left-turn one-way hydraulic control valve is connected with the steering valve group, and is connected with the A ports of the third throttle valve and the fourth throttle valve, and the X port of the left-turn one-way hydraulic control valve is connected with the A port of the first three-position four-way electromagnetic valve.

[0027] As a further preferred embodiment of the present application, the steering valve group comprises a two-position four-way manual reversing valve and a second three-position four-way electromagnetic valve, wherein:

[0028] The P port of the two-position four-way manual reversing valve is connected with the main oil path, the T port of the two-position four-way manual reversing valve is connected with the oil return path, the A port of the two-position four-way manual reversing valve is connected with the P port of the first three-position four-way electromagnetic valve, and the A port of the two-position four-way manual reversing valve is connected with the remote control port of the second three-position four-way electromagnetic valve, and the B port of the two-position four-way manual reversing valve is connected with the P port of the second three-position four-way electromagnetic valve;

[0029] The T port of the second three-position four-way electromagnetic valve is connected with the oil return path, the A port of the second three-position four-way electromagnetic valve is connected with the synchronization valve group, and the B port of the second three-position four-way electromagnetic valve is connected with the synchronization valve group.

[0030] As a further preferred embodiment of the present application, the synchronization valve group comprises a right-turn synchronization valve group, a left-turn synchronization valve group, a left-side reciprocating double-piston rod hydraulic cylinder, and a right-side reciprocating double-piston rod hydraulic cylinder, wherein:

[0031] The right-turn synchronization valve group has a first throttle valve and a second throttle valve that operate synchronously, the A ports of the first throttle valve and the second throttle valve are both connected with the A port of the second three-position four-way electromagnetic valve, and the A ports of the first throttle valve and the second throttle valve are both connected with the B port of the right-turn one-way hydraulic control valve, the B port of the first throttle valve is connected with the lower oil chamber of the left-side reciprocating double-piston rod hydraulic cylinder, and the B port of the second throttle valve is connected with the upper oil chamber of the right-side reciprocating double-piston rod hydraulic cylinder;

[0032] The left-turn road synchronous valve group has a third throttle valve and a fourth throttle valve synchronously operating, the A port of the third throttle valve and the A port of the fourth throttle valve are connected with the B port of the second three-position four-way electromagnetic valve, and the A port of the third throttle valve and the A port of the fourth throttle valve are connected with the B port of the left-turn road one-way hydraulic control valve, the B port of the third throttle valve is connected with the lower oil chamber of the right reciprocating double-piston rod hydraulic cylinder, and the B port of the fourth throttle valve is connected with the upper oil chamber of the left reciprocating double-piston rod hydraulic cylinder.

[0033] As a further preferred embodiment of the application, a pump port relief valve, a right-turn road relief valve and a left-turn road relief valve are further included, wherein:

[0034] The P port of the pump port relief valve is connected with the main oil circuit, and the T port of the pump port relief valve is connected with the oil return circuit;

[0035] The P port of the right-turn road relief valve is connected on the pipeline between the right-turn road one-way hydraulic control valve and the synchronous valve group, and the T port of the right-turn road relief valve is connected with the oil return circuit;

[0036] The P port of the left-turn road relief valve is connected on the pipeline between the left-turn road one-way hydraulic control valve and the synchronous valve group, and the T port of the left-turn road relief valve is connected with the oil return circuit.

[0037] As a further preferred embodiment of the application, the walking hydraulic system includes a first four-position four-way electromagnetic valve, a second four-position four-way electromagnetic valve, a fifth throttle valve, a sixth throttle valve, a seventh throttle valve, an eighth throttle valve, a first hydraulic motor, a second hydraulic motor, a third hydraulic motor, a fourth hydraulic motor, a three-position three-way electromagnetic valve, a third relief valve, a fourth relief valve, a fifth relief valve, a third one-way valve and a fourth one-way valve, wherein:

[0038] The P port of the first four-position four-way electromagnetic valve is connected with the main oil circuit, and the T port of the first four-position four-way electromagnetic valve is connected with the oil return circuit;

[0039] The P port of the second four-position four-way electromagnetic valve is connected with the main oil circuit, and the T port of the second four-position four-way electromagnetic valve is connected with the oil return circuit;

[0040] The A ports of the fifth throttle valve and the sixth throttle valve are connected with the A port of the first four-position four-way electromagnetic valve, the B port of the fifth throttle valve is connected with one end of the first hydraulic motor, the B port of the sixth throttle valve is connected with one end of the second hydraulic motor, and the other end of the first hydraulic motor and the other end of the second hydraulic motor are both connected with the B port of the first four-position four-way electromagnetic valve;

[0041] The A ports of the seventh throttle valve and the eighth throttle valve are connected with the A port of the second four-position four-way electromagnetic valve, the B port of the seventh throttle valve is connected with one end of the third hydraulic motor, the B port of the eighth throttle valve is connected with one end of the fourth hydraulic motor, and the other end of the third hydraulic motor and the other end of the fourth hydraulic motor are both connected with the B port of the second four-position four-way electromagnetic valve;

[0042] The P port of the three-position three-way electromagnetic valve is connected with the main oil circuit, and the T port of the three-position three-way electromagnetic valve is connected with the oil return circuit.

[0043] The P port of the third overflow valve is connected with the A port of the three-position three-way electromagnetic valve, and the T port of the third overflow valve is connected with the oil return circuit.

[0044] The P port of the fourth overflow valve is connected with the A port of the first four-position four-way electromagnetic valve, and the T port of the fourth overflow valve is connected with the oil return circuit.

[0045] The P port of the fifth overflow valve is connected with the A port of the second four-position four-way electromagnetic valve, and the T port of the fifth overflow valve is connected with the oil return circuit.

[0046] The third one-way valve is arranged on a pipeline connected with the T port of the fourth overflow valve, and the fourth one-way valve is arranged on a pipeline connected with the T port of the fifth overflow valve.

[0047] The working method of the small loader hydraulic system with the integrated pressure maintaining and safety overflow function also comprises two filters, a hydraulic pump and a heat dissipation fan, one filter and the hydraulic pump are arranged on the main oil circuit, and the other filter and the heat dissipation fan are arranged on the oil return circuit.

[0048] The working method of the small loader hydraulic system comprises a working method of a boom lifting hydraulic system and a working method of a steering hydraulic system.

[0049] The working method of the boom lifting hydraulic system has four working conditions, which are as follows.

[0050] Working condition one, when the loader boom is normally lifted

[0051] The first three-position four-way manual reversing valve is connected with the left position, the A port of the first three-position four-way manual reversing valve is communicated with the P port, and the B port is communicated with the T port, at this time, due to the operation of the hydraulic pump, the hydraulic oil is pumped out, so that the second two-position two-way reversing valve and the first two-position two-way reversing valve sense the pressure of the hydraulic control port, and the valve core of the second two-position two-way reversing valve is pushed to the left and the valve core of the first two-position two-way reversing valve is pushed to the right, so that the second two-position two-way reversing valve and the first two-position two-way reversing valve are connected with the oil circuit.

[0052] The pressure oil flows from the P port of the first three-position four-way manual reversing valve to the lifting circuit adjustable throttle valve and the lifting circuit one-way valve through the working oil port A port, and then flows into the left oil chamber of the second single piston rod hydraulic cylinder and the first single piston rod hydraulic cylinder through the second two-position two-way reversing valve.

[0053] The oil in the right oil chamber of the second single piston rod hydraulic cylinder and the first single piston rod hydraulic cylinder flows through the first two-position two-way reversing valve to the descending circuit adjustable throttle valve, and finally flows into the oil tank through the B port of the first three-position four-way manual reversing valve.

[0054] Before the pistons of the second single-piston-rod hydraulic cylinder and the first single-piston-rod hydraulic cylinder move to the rightmost end, i.e. before the boom reaches the maximum lifting height, neither the second check valve nor the first check valve works;

[0055] Case two, when the boom is lifted to the maximum stroke, the hydraulic pump is still supplying oil

[0056] When the pistons of the second single-piston-rod hydraulic cylinder and the first single-piston-rod hydraulic cylinder move to the rightmost end and the operator still controls the boom to continue lifting, the hydraulic oil flows to the second overflow valve through the second two-position two-way directional valve, at this time, the pressure in the pipeline is higher than the set pressure of the second overflow valve, therefore, the oil pushes the main valve core of the second overflow valve through the first check valve to the adjustable throttle valve of the lowering circuit, and finally flows into the oil tank through the B port of the first three-position four-way manual directional valve;

[0057] At the same time, the solenoid of the second two-position two-way electromagnetic directional valve with a lever control is electrified to the left position, and the remote pressure regulating port of the lifting circuit safety overflow valve is directly connected to the oil tank, at this time, the lifting circuit safety overflow valve is discharged due to the pipeline pressure being greater than the remote pressure regulating port setting pressure;

[0058] Case two, the second overflow valve and the lifting circuit safety overflow valve jointly discharge, forming double safety overflow;

[0059] Case three, when the loader needs to maintain the current work

[0060] The first three-position four-way manual directional valve is connected to the middle position, and the pressure oil flows into the first three-position four-way manual directional valve from the P port, and is directly returned to the oil tank through the T port, at this time, the hydraulic oil pressure is reduced;

[0061] The second two-position two-way directional valve senses that the pressure is insufficient to keep the valve core in the left position, and returns to the right position under the action of the spring, at this time, the pressure in the original pipeline is mainly borne by the second two-position two-way directional valve, and the first three-position four-way manual directional valve does not directly bear the pressure of the second single-piston-rod hydraulic cylinder and the first single-piston-rod hydraulic cylinder, but only bears the oil pressure in the original pipeline;

[0062] If the second two-position two-way directional valve is discharged due to failure, at this time, the first three-position four-way manual directional valve can still ensure that the pipeline has pressure maintaining function, and the second two-position two-way directional valve and the first three-position four-way manual directional valve form double pressure maintaining;

[0063] And the first overflow valve, the first check valve, the second overflow valve and the second check valve can also ensure that the second two-position two-way directional valve and the first three-position four-way manual directional valve simultaneously fail to discharge and increase the pressure to suddenly reduce the cavitation phenomenon;

[0064] Case four, when the loader cannot start due to failure

[0065] The valve core of the second lever-controlled two-position two-way electromagnetic reversing valve is in the right position by manual adjustment, so that the lifting circuit safety overflow valve is communicated with the tank. At this time, because the pressure of the oil line connected to the P port of the lifting circuit safety overflow valve is higher than the set pressure at the Y remote pressure regulating port, the main valve core of the lifting circuit safety overflow valve is lifted, oil is discharged, and the boom falls for maintenance;

[0066] The working method of the steering hydraulic system has five working conditions, which are as follows:

[0067] Working condition one: when the loader is straight driving

[0068] The steering valve group is in the original position, the two-position four-way manual reversing valve is connected to the right position, the second three-position four-way electromagnetic valve is connected to the middle position, and the pressure oil flows from the A port of the two-position four-way manual reversing valve, enters the P port of the second three-position four-way electromagnetic valve through the B port, and finally flows back to the tank through the T port of the second three-position four-way electromagnetic valve;

[0069] Working condition one: the full hydraulic steering gear does not work;

[0070] Working condition two: when the loader turns left in normal state

[0071] The two-position four-way manual reversing valve is connected to the left position, and the pressure oil flows from the P port of the two-position four-way manual reversing valve to the A port and then enters the full hydraulic steering gear. At this time, the remote pressure regulating port of the second three-position four-way electromagnetic valve controlled by the hydraulic pressure senses the pressure and pushes the valve core to move right, and the second three-position four-way electromagnetic valve is connected to the right position. The pressure oil flows from the A port of the second three-position four-way electromagnetic valve to the P port, flows into the B port of the two-position four-way manual reversing valve, and flows out from the T port. Another part flows from the B port of the second three-position four-way electromagnetic valve to the T port and flows back to the tank. At this time, the first three-position four-way electromagnetic valve is electrified on the left side, pushes the valve core to move right, and the first three-position four-way electromagnetic valve is connected to the left position. The pressure oil enters the P port of the first three-position four-way electromagnetic valve, flows to the B port, enters the left turn path synchronization valve group through the left turn path one-way hydraulic control valve, and simultaneously enters the upper cavity part of the left reciprocating double piston rod hydraulic cylinder and the lower cavity part of the right reciprocating double piston rod hydraulic cylinder. Under the push of the pressure oil, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward, and the loader turns left;

[0072] Working condition three: when the loader turns left in an emergency

[0073] The two-position four-way manual reversing valve remains in the original position, and the pressure oil flows from the P port of the two-position four-way manual reversing valve to the B port. There is no pressure oil flowing through the oil line connected to the A port of the two-position four-way manual reversing valve. At this time, the remote pressure regulating port of the second three-position four-way electromagnetic valve controlled by the hydraulic pressure does not work, and the valve core position of the second three-position four-way electromagnetic valve is controlled by the manual lever;

[0074] When the loader is turning right in normal state, the second three-position four-way electromagnetic valve is connected with the right position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve to the P port of the second three-position four-way electromagnetic valve, and then flows to the right turning road synchronous valve group through the second three-position four-way electromagnetic valve. Since the pressure loss is small without passing through the full hydraulic steering gear, the pressure oil enters the lower cavity part of the left reciprocating double piston rod hydraulic cylinder and the upper cavity part of the right reciprocating double piston rod hydraulic cylinder at the same time, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward rapidly, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward rapidly, and the loader turns right rapidly.

[0075] When the loader is turning right in normal state, the second three-position four-way electromagnetic valve is connected with the right position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve to the P port of the second three-position four-way electromagnetic valve, and then flows to the right turning road synchronous valve group through the second three-position four-way electromagnetic valve. Since the pressure loss is small without passing through the full hydraulic steering gear, the pressure oil enters the lower cavity part of the left reciprocating double piston rod hydraulic cylinder and the upper cavity part of the right reciprocating double piston rod hydraulic cylinder at the same time, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward rapidly, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward rapidly, and the loader turns right rapidly.

[0076] When the loader is turning right in normal state, the second three-position four-way electromagnetic valve is connected with the right position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve to the P port of the second three-position four-way electromagnetic valve, and then flows to the right turning road synchronous valve group through the second three-position four-way electromagnetic valve. Since the pressure loss is small without passing through the full hydraulic steering gear, the pressure oil enters the lower cavity part of the left reciprocating double piston rod hydraulic cylinder and the upper cavity part of the right reciprocating double piston rod hydraulic cylinder at the same time, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward rapidly, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward rapidly, and the loader turns right rapidly.

[0077] When the loader is turning right in normal state, the second three-position four-way electromagnetic valve is connected with the right position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve to the P port of the second three-position four-way electromagnetic valve, and then flows to the right turning road synchronous valve group through the second three-position four-way electromagnetic valve. Since the pressure loss is small without passing through the full hydraulic steering gear, the pressure oil enters the lower cavity part of the left reciprocating double piston rod hydraulic cylinder and the upper cavity part of the right reciprocating double piston rod hydraulic cylinder at the same time, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward rapidly, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward rapidly, and the loader turns right rapidly.

[0078] When the loader is turning right in normal state, the second three-position four-way electromagnetic valve is connected with the right position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve to the P port of the second three-position four-way electromagnetic valve, and then flows to the right turning road synchronous valve group through the second three-position four-way electromagnetic valve. Since the pressure loss is small without passing through the full hydraulic steering gear, the pressure oil enters the lower cavity part of the left reciprocating double piston rod hydraulic cylinder and the upper cavity part of the right reciprocating double piston rod hydraulic cylinder at the same time, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward rapidly, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward rapidly, and the loader turns right rapidly.

[0079] When the loader is turning right in normal state, the second three-position four-way electromagnetic valve is connected with the right position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve to the P port of the second three-position four-way electromagnetic valve, and then flows to the right turning road synchronous valve group through the second three-position four-way electromagnetic valve. Since the pressure loss is small without passing through the full hydraulic steering gear, the pressure oil enters the lower cavity part of the left reciprocating double piston rod hydraulic cylinder and the upper cavity part of the right reciprocating double piston rod hydraulic cylinder at the same time, the piston of the left reciprocating double piston rod hydraulic cylinder moves downward rapidly, the piston of the right reciprocating double piston rod hydraulic cylinder moves upward rapidly, and the loader turns right rapidly.

[0080] By the above technical scheme, relative to the prior art, the present application has the following beneficial effects:

[0081] 1. The present application designs a double safety overflow valve group for the large arm lifting system, which can not only avoid the damage of the hydraulic cylinder caused by the sudden disappearance of pressure oil liquid due to the failure of the reversing valve when the large arm is kept in action, but also can perform overflow protection in the case of pressure rise caused by the continuous input of pressure oil liquid by the hydraulic pump when the working oil cylinder piston reaches the maximum stroke, and can also safely release pressure when the loader fails or is not started, so as to make the large arm descend for troubleshooting or maintenance. The overflow valve can be used in multiple ways, and plays different roles in different situations.

[0082] 2. The present application adds a hydraulic control with a spring return reversing valve (i.e. a second two-position two-way electromagnetic reversing valve with lever control) on the large arm lifting inlet line, which not only protects the large arm lifting hydraulic controller and concentrates the pressure mainly on this reversing valve, but also cooperates with the large arm lifting hydraulic controller (a first three-position four-way manual reversing valve) to form a double pressure protection design.

[0083] 3. The present application optimizes the design of the steering hydraulic system, designs a steering valve group, and increases the emergency steering function. Through simulation, the steering action can be completed at 3 times the original steering speed, greatly improving the emergency obstacle avoidance performance of the loader.

[0084] 4. The present application designs a cleaning device in the traveling hydraulic system, which uses pressure oil to flush the pipeline and keep the pipeline clean.

[0085] 5. The present application adopts different oil supply strategies for different hydraulic systems, uses a plunger pump to supply oil to the hydraulic system working at high pressure, and uses a double gear pump to supply oil to the traveling and steering hydraulic systems with low working pressure. According to the working characteristics, the hydraulic pump is selected, which improves the working efficiency and reliability. BRIEF DESCRIPTION OF DRAWINGS

[0086] The present application will be further described below in combination with the drawings and examples.

[0087] Figure 1 is a schematic diagram of the overall structure of the loader hydraulic system of the present application;

[0088] Figure 2 is a schematic diagram of the overall structure of the large arm lifting hydraulic system of the present application;

[0089] Figure 3 is a schematic diagram of the overall structure of the steering hydraulic system of the present application;

[0090] Figure 4 is a schematic diagram of the overall structure of the traveling hydraulic system of the present application;

[0091] Figure 5Is the overall structure schematic diagram of the big arm extension hydraulic system or the big arm bucket hydraulic system of the present application;

[0092] Figure 6 Is the oil flow direction diagram when the big arm lifting hydraulic system of the present application is lifted;

[0093] Figure 7 Is the oil flow direction diagram when the big arm lifting hydraulic system of the present application is lowered;

[0094] Figure 8 Is the oil flow direction diagram when the piston of the big arm lifting hydraulic system of the present application moves to the rightmost end;

[0095] Figure 9 Is the oil flow direction diagram when the piston of the big arm lifting hydraulic system of the present application moves to the leftmost end;

[0096] Figure 10 Is the oil flow direction diagram when the steering hydraulic system of the present application turns left under normal circumstances;

[0097] Figure 11 Is the oil flow direction diagram when the steering hydraulic system of the present application turns right under normal circumstances;

[0098] Figure 12 Is the oil flow direction diagram when the steering hydraulic system of the present application turns left under emergency circumstances;

[0099] Figure 13 Is the oil flow direction diagram when the steering hydraulic system of the present application turns right under emergency circumstances;

[0100] Figure 14 Is the oil flow direction diagram when the walking hydraulic system of the present application turns right;

[0101] Figure 15 Is the oil flow direction diagram when the walking hydraulic system of the present application turns left.

[0102] In the figure:

[0103] 100, oil tank; 101, first two-position two-way electromagnetic reversing valve; 102, first direct-acting overflow valve; 103, second two-position two-way electromagnetic reversing valve; 104, second direct-acting overflow valve; 105, third direct-acting overflow valve; 106, filter; 107, hydraulic pump; 108, heat dissipation fan;

[0104] 200. boom raising hydraulic system; 201. first three-position four-way hand-operated directional valve; 202. first single-piston-rod hydraulic cylinder; 203. second single-piston-rod hydraulic cylinder; 204. raising circuit adjustable throttle valve; 205. second two-position two-way directional valve; 206. raising circuit check valve; 207. lowering circuit adjustable throttle valve; 208. first two-position two-way directional valve; 209. lowering circuit check valve; 210. first pipeline; 211. second relief valve; 212. first relief valve; 213. second check valve; 214. first check valve; 215. lowering circuit safety relief valve; 216. first two-position two-way electromagnetic directional valve with lever control; 217. raising circuit safety relief valve; 218. second two-position two-way electromagnetic directional valve with lever control;

[0105] 300. steering hydraulic system; 301. full hydraulic steering gear; 302. steering valve group; 303. synchronization valve group; 304. first three-position four-way electromagnetic valve; 305. right turning circuit check valve with hydraulic control; 306. left turning circuit check valve with hydraulic control; 307. two-position four-way hand-operated directional valve; 308. second three-position four-way electromagnetic valve; 309. right turning circuit synchronization valve group; 310. left turning circuit synchronization valve group; 311. left reciprocating double-piston-rod hydraulic cylinder; 312. right reciprocating double-piston-rod hydraulic cylinder; 313. first throttle valve; 314. second throttle valve; 315. third throttle valve; 316. fourth throttle valve; 317. pump port relief valve; 318. right turning circuit relief valve; 319. left turning circuit relief valve;

[0106] 400. traveling hydraulic system; 401. first four-position four-way electromagnetic valve; 402. second four-position four-way electromagnetic valve; 403. fifth throttle valve; 404. sixth throttle valve; 405. seventh throttle valve; 406. eighth throttle valve; 407. first hydraulic motor; 408. second hydraulic motor; 409. third hydraulic motor; 410. fifth hydraulic motor; 411. three-position three-way electromagnetic valve; 412. third relief valve; 413. fourth relief valve; 414. fifth relief valve; 415. third check valve; 416. fourth check valve;

[0107] 500, boom extension and bucket hydraulic system; 501, boom extension hydraulic system; 502, boom bucket hydraulic system; 503, second three-position four-way hand-operated directional valve; 504, first adjustable throttle valve; 505, fifth check valve; 506, fourth direct-acting overflow valve; 507, third two-position two-way directional valve; 508, first safety overflow valve; 509, third single-rod hydraulic cylinder; 510, fourth single-rod hydraulic cylinder; 511, fourth two-position two-way directional valve; 512, fifth direct-acting overflow valve; 513, second adjustable throttle valve; 514, second safety overflow valve; 515, sixth check valve; 516, seventh check valve; 517, eighth check valve; 518, second pipeline. DETAILED DESCRIPTION

[0108] The application will be further described below in conjunction with the drawings. These drawings are simplified schematic diagrams and only schematically show the basic structure of the application, and thus only show the components related to the application.

[0109] In the description of the application, it should be understood that the terms "left side", "right side", "upper portion", "lower portion" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and "first", "second" and the like do not represent the importance of the parts, and thus cannot be understood as a limitation on the application. The specific dimensions used in this embodiment are only for the purpose of illustrating the technical scheme and do not limit the protection scope of the application. Example 1

[0110] This embodiment provides a preferred embodiment of a small-sized loader hydraulic system integrated with pressure maintaining and safety overflow functions, as shown in Figures 1 to 15 The loader hydraulic system includes an oil tank 100, a main oil circuit and a return oil circuit, the main oil circuit is connected to the outlet end of the oil tank 100, and the return oil circuit is connected to the inlet end of the oil tank 100.

[0111] The loader hydraulic system includes a boom lifting hydraulic system 200, a steering hydraulic system 300, a traveling hydraulic system 400, and a boom extension and bucket hydraulic system 500. The boom lifting hydraulic system 200, the steering hydraulic system 300, the traveling hydraulic system 400, and the boom extension and bucket hydraulic system 500 are connected to the main oil circuit at the oil inlet end and connected to the oil return circuit at the oil outlet end. A first two-position two-way electromagnetic directional valve 101 is arranged on the main oil circuit between the boom lifting hydraulic system 200 and the oil tank 100. The first two-position two-way electromagnetic directional valve 101 controls the communication state of the main oil circuit between the boom lifting hydraulic system 200 and the oil tank 100. The first direct-acting overflow valve 102 is also arranged. The P port of the first direct-acting overflow valve 102 is connected to the P port of the first two-position two-way electromagnetic directional valve 101, and the T port of the first direct-acting overflow valve 102 is connected to the oil return circuit. The first direct-acting overflow valve 102 protects the oil pump and prevents the oil circuit from being blocked or damaged due to high pressure.

[0112] The boom extension and bucket hydraulic system 500 includes a boom extension hydraulic system 501 and a boom bucket hydraulic system 502. The boom extension hydraulic system 501 and the boom bucket hydraulic system 502 are connected to the oil tank 100 through the main oil circuit. A second two-position two-way electromagnetic directional valve 103 is arranged on the main oil circuit between the boom extension hydraulic system 501 and the oil tank 100 and on the main oil circuit between the boom bucket hydraulic system 502 and the oil tank 100. The second two-position two-way electromagnetic directional valve 103 controls the communication state of the main oil circuit between the boom extension hydraulic system 501 and the oil tank 100 and the communication state of the main oil circuit between the boom bucket hydraulic system 502 and the oil tank 100. The second direct-acting overflow valve 104 and the third direct-acting overflow valve 105 are also arranged. The P port of the second two-position two-way electromagnetic directional valve 103 on the main oil circuit between the boom bucket hydraulic system 502 and the oil tank 100 is connected to the P port of the second direct-acting overflow valve 104, and the T port of the second direct-acting overflow valve 104 is connected to the oil return circuit. The second direct-acting overflow valve 104 protects the oil pump and prevents the oil circuit from being blocked or damaged due to high pressure. The P port of the second two-position two-way electromagnetic directional valve 103 on the main oil circuit between the boom extension hydraulic system 501 and the oil tank 100 is connected to the P port of the third direct-acting overflow valve 105, and the T port of the third direct-acting overflow valve 105 is connected to the oil return circuit. The third direct-acting overflow valve 105 protects the oil pump and prevents the oil circuit from being blocked or damaged due to high pressure.

[0113] The boom lifting hydraulic system 200 includes a boom lifting hydraulic system body and a double safety overflow valve group. The boom lifting hydraulic system body controls the lifting of the boom. The double safety overflow valve group prevents the "cylinder blocking" phenomenon and prevents the continuous rise of the oil circuit pressure when the boom lifting hydraulic system body is operating at the maximum stroke and continues to lift, thereby protecting the hydraulic components. The specific structure of the boom lifting hydraulic system 200 is as follows:

[0114] The boom lifting hydraulic system body includes a first three-position four-way manual reversing valve 201, a first single piston rod hydraulic cylinder 202, a second single piston rod hydraulic cylinder 203, a lifting circuit adjustable throttle valve 204, a second two-position two-way reversing valve 205, a lifting circuit check valve 206, a lowering circuit adjustable throttle valve 207, a first two-position two-way reversing valve 208, and a lowering circuit check valve 209.

[0115] The P port of the first three-position four-way manual reversing valve 201 is connected to the main oil circuit, and the T port of the first three-position four-way manual reversing valve 201 is connected to the return oil circuit. The A port of the first three-position four-way manual reversing valve 201 is connected to the left oil chamber of the first single piston rod hydraulic cylinder 202, and simultaneously connected to the left oil chamber of the second single piston rod hydraulic cylinder 203. The B port of the first three-position four-way manual reversing valve 201 is connected to the right oil chamber of the first single piston rod hydraulic cylinder 202, and simultaneously connected to the right oil chamber of the second single piston rod hydraulic cylinder 203.

[0116] The lifting circuit adjustable throttle valve 204 and the second two-position two-way reversing valve 205 are sequentially arranged along the oil circuit direction (i.e., the direction from the first three-position four-way manual reversing valve 201 to the first single piston rod hydraulic cylinder 202) on the pipeline connecting the A port of the first three-position four-way manual reversing valve 201 to the first single piston rod hydraulic cylinder 202 and the second single piston rod hydraulic cylinder 203. Specifically, the A port of the lifting circuit adjustable throttle valve 204 is connected to the A port of the first three-position four-way manual reversing valve 201, the B port of the lifting circuit adjustable throttle valve 204 is connected to the P port of the second two-position two-way reversing valve 205, and the A port of the second two-position two-way reversing valve 205 is connected to the left oil chamber of the first single piston rod hydraulic cylinder 202 and simultaneously connected to the left oil chamber of the second single piston rod hydraulic cylinder 203. The lifting circuit check valve 206 is connected in parallel to the lifting circuit adjustable throttle valve 204, and the lifting circuit check valve 206 is the main hydraulic component through which the pressure oil passes when it is the inlet oil circuit.

[0117] The lowering circuit adjustable throttle valve 207 is connected with the B port of the first three-position four-way manual reversing valve 201 and the first single piston rod hydraulic cylinder 202 and the second single piston rod hydraulic cylinder 203. The lowering circuit adjustable throttle valve 207 is connected with the B port of the first three-position four-way manual reversing valve 201, the B port of the lowering circuit adjustable throttle valve 207 is connected with the P port of the first two-position two-way reversing valve 208, the A port of the first two-position two-way reversing valve 208 is connected with the right oil cavity of the first single piston rod hydraulic cylinder 202, and is also connected with the right oil cavity of the second single piston rod hydraulic cylinder 203. The lowering circuit check valve 209 is connected with the lowering circuit adjustable throttle valve 207 in parallel, and the lowering circuit check valve 209 is the main hydraulic element through which the pressure oil passes when the lowering circuit check valve 209 is used as an oil inlet.

[0118] The double safety overflow valve group includes a first pipeline 210, a second overflow valve 211 with a remote pressure regulating port, a first overflow valve 212 with a remote pressure regulating port, a second check valve 213, a first check valve 214, a lowering circuit safety overflow valve 215, a first two-position two-way electromagnetic reversing valve 216 with a lever control, a lifting circuit safety overflow valve 217, and a second two-position two-way electromagnetic reversing valve 218 with a lever control.

[0119] The pipeline connected with the P port of the second two-position two-way reversing valve 205 is connected with the pipeline connected with the P port of the first two-position two-way reversing valve 208 through the first pipeline 210. The second overflow valve 211 and the first overflow valve 212 are arranged in sequence on the first pipeline 210 in the direction from the second two-position two-way reversing valve 205 to the first two-position two-way reversing valve 208, the second overflow valve 211 is connected with the second check valve 213 in parallel, and the first overflow valve 212 is connected with the first check valve 214 in parallel.

[0120] The right oil cavities of the first single piston rod hydraulic cylinder 202 and the second single piston rod hydraulic cylinder 203 are connected with the P port of the lowering circuit safety overflow valve 215, the T port of the lowering circuit safety overflow valve 215 is connected with an oil return pipeline, the Y port of the lowering circuit safety overflow valve 215 is connected with the P port of the first two-position two-way electromagnetic reversing valve 216 with a lever control, and the A port of the first two-position two-way electromagnetic reversing valve 216 with a lever control is connected with the oil return pipeline. The lowering circuit safety overflow valve 215 and the first two-position two-way electromagnetic reversing valve 216 with a lever control work together to avoid high pressure safety overflow during normal work and release pressure for maintenance during failure according to the different positions of the valve core of the two-position two-way electromagnetic reversing valve 216.

[0121] The left oil cavity of the first single-piston-rod hydraulic cylinder 202 and the second single-piston-rod hydraulic cylinder 203 is connected with the P port of the lifting circuit safety overflow valve 217, the T port of the lifting circuit safety overflow valve 217 is connected with the oil return circuit, the Y port of the lifting circuit safety overflow valve 217 is connected with the P port of the second two-position two-way electromagnetic reversing valve with a lever control 218, and the A port of the second two-position two-way electromagnetic reversing valve with a lever control 218 is connected with the oil return circuit. The lifting circuit safety overflow valve 217 and the second two-position two-way electromagnetic reversing valve with a lever control 218 work together to avoid high pressure overflow during normal operation and release pressure for maintenance during failure according to the different positions of the valve core of the two-position two-way electromagnetic reversing valve 218.

[0122] The above-mentioned steering hydraulic system 300 includes a full hydraulic steering gear 301, a steering valve group 302, and a synchronization valve group 303. The full hydraulic steering gear 301, the steering valve group 302, and the synchronization valve group 303 work together to realize the pressure maintaining function. The specific structure of the steering hydraulic system 300 is as follows:

[0123] The above-mentioned full hydraulic steering gear 301 includes a first three-position four-way electromagnetic valve 304, a right-turn one-way hydraulic control valve 305, and a left-turn one-way hydraulic control valve 306. The A port of the first three-position four-way electromagnetic valve 304 is connected with the A port of the right-turn one-way hydraulic control valve 305, the B port of the first three-position four-way electromagnetic valve 304 is connected with the A port of the left-turn one-way hydraulic control valve 306, the P port of the first three-position four-way electromagnetic valve 304 is connected with the steering valve group 302, and the T port of the first three-position four-way electromagnetic valve 304 is connected with the oil return circuit. The B port of the right-turn one-way hydraulic control valve 305 is connected with the steering valve group 302 and the right-turn synchronization valve group 309, and the X port of the right-turn one-way hydraulic control valve 305 is connected with the B port of the first three-position four-way electromagnetic valve 304. The B port of the left-turn one-way hydraulic control valve 306 is connected with the steering valve group 302 and the left-turn synchronization valve group 310, and the X port of the left-turn one-way hydraulic control valve 306 is connected with the A port of the first three-position four-way electromagnetic valve 304.

[0124] The steering valve group 302 includes a two-position four-way manual reversing valve 307 and a second three-position four-way electromagnetic valve 308. The P port of the two-position four-way manual reversing valve 307 is connected with the main oil circuit, the T port of the two-position four-way manual reversing valve 307 is connected with the oil return circuit, the A port of the two-position four-way manual reversing valve 307 is connected with the P port of the first three-position four-way electromagnetic valve 304 and the remote control port of the second three-position four-way electromagnetic valve 308, and the B port of the two-position four-way manual reversing valve 307 is connected with the P port of the second three-position four-way electromagnetic valve 308. The T port of the second three-position four-way electromagnetic valve 308 is connected with the oil return circuit, the A port of the second three-position four-way electromagnetic valve 308 is connected with the synchronization valve group 303, and the B port of the second three-position four-way electromagnetic valve 308 is connected with the synchronization valve group 303.

[0125] The synchronization valve group 303 includes a right-turn path synchronization valve group 309, a left-turn path synchronization valve group 310, a left-side reciprocating double-piston rod hydraulic cylinder 311, and a right-side reciprocating double-piston rod hydraulic cylinder 312. The right-turn path synchronization valve group 309 has a first throttle valve 313 and a second throttle valve 314 that operate synchronously, the A port of the first throttle valve 313 and the A port of the second throttle valve 314 are both connected to the A port of the second three-position four-way electromagnetic valve 308, and the A port of the first throttle valve 313 and the A port of the second throttle valve 314 are both connected to the B port of the right-turn path one-way hydraulic control valve 305, the B port of the first throttle valve 313 is connected to the lower oil chamber of the left-side reciprocating double-piston rod hydraulic cylinder 311, and the B port of the second throttle valve 314 is connected to the upper oil chamber of the right-side reciprocating double-piston rod hydraulic cylinder 312. The left-turn path synchronization valve group 310 has a third throttle valve 315 and a fourth throttle valve 316 that operate synchronously, the A port of the third throttle valve 315 and the A port of the fourth throttle valve 316 are both connected to the B port of the second three-position four-way electromagnetic valve 308, and the A port of the third throttle valve 315 and the A port of the fourth throttle valve 316 are both connected to the B port of the left-turn path one-way hydraulic control valve 306, the B port of the third throttle valve 315 is connected to the lower oil chamber of the right-side reciprocating double-piston rod hydraulic cylinder 312, and the B port of the fourth throttle valve 316 is connected to the upper oil chamber of the left-side reciprocating double-piston rod hydraulic cylinder 311.

[0126] The hydraulic system 300 of the present embodiment further includes a pump port overflow valve 317, a right-turn path overflow valve 318, and a left-turn path overflow valve 319. The pump port overflow valve 317 can prevent the oil path from being damaged by excessive pressure due to blockage or other conditions, the right-turn path overflow valve 318 can prevent the right-turn oil path from being damaged by excessive pressure due to blockage or other conditions, and the left-turn path overflow valve 319 can prevent the left-turn oil path from being damaged by excessive pressure due to blockage or other conditions. The P port of the pump port overflow valve 317 is connected to the main oil path, and the T port of the pump port overflow valve 317 is connected to the oil return path. The P port of the right-turn path overflow valve 318 is connected to the pipeline between the right-turn path one-way hydraulic control valve 305 and the synchronization valve group 303, and the T port of the right-turn path overflow valve 318 is connected to the oil return path. The P port of the left-turn path overflow valve 319 is connected to the pipeline between the left-turn path one-way hydraulic control valve 306 and the synchronization valve group 303, and the T port of the left-turn path overflow valve 319 is connected to the oil return path.

[0127] The above-described traveling hydraulic system 400 includes a first four-position four-way electromagnetic valve 401, a second four-position four-way electromagnetic valve 402, a fifth throttle valve 403, a sixth throttle valve 404, a seventh throttle valve 405, an eighth throttle valve 406, a first hydraulic motor 407, a second hydraulic motor 408, a third hydraulic motor 409, a fourth hydraulic motor 410, a three-position three-way electromagnetic valve 411, a third overflow valve 412, a fourth overflow valve 413, a fifth overflow valve 414, a third one-way valve 415, and a fourth one-way valve 416.

[0128] The P port of the first four-position four-way electromagnetic valve 401 is connected with the main oil circuit, and the T port of the first four-position four-way electromagnetic valve 401 is connected with the return oil circuit. The P port of the second four-position four-way electromagnetic valve 402 is connected with the main oil circuit, and the T port of the second four-position four-way electromagnetic valve 402 is connected with the return oil circuit. The A ports of the fifth throttle valve 403 and the sixth throttle valve 404 are connected with the A port of the first four-position four-way electromagnetic valve 401, the B port of the fifth throttle valve 403 is connected with one end of the first hydraulic motor 407, the B port of the sixth throttle valve 404 is connected with one end of the second hydraulic motor 408, and the other end of the first hydraulic motor 407 and the other end of the second hydraulic motor 408 are connected with the B port of the first four-position four-way electromagnetic valve 401. The A ports of the seventh throttle valve 405 and the eighth throttle valve 406 are connected with the A port of the second four-position four-way electromagnetic valve 402, the B port of the seventh throttle valve 405 is connected with one end of the third hydraulic motor 409, the B port of the eighth throttle valve 406 is connected with one end of the fourth hydraulic motor 410, and the other end of the third hydraulic motor 409 and the other end of the fourth hydraulic motor 410 are connected with the B port of the second four-position four-way electromagnetic valve 402. The P port of the three-position three-way electromagnetic valve 411 is connected with the main oil circuit, and the T port of the three-position three-way electromagnetic valve 411 is connected with the return oil circuit.

[0129] The P port of the third overflow valve 412 is connected with the A port of the three-position three-way electromagnetic valve 411, and the T port of the third overflow valve 412 is connected with the return oil circuit. The P port of the fourth overflow valve 413 is connected with the A port of the first four-position four-way electromagnetic valve 401, and the T port of the fourth overflow valve 413 is connected with the return oil circuit. The P port of the fifth overflow valve 414 is connected with the A port of the second four-position four-way electromagnetic valve 402, and the T port of the fifth overflow valve 414 is connected with the return oil circuit. The third check valve 415 is arranged on the pipeline connected with the T port of the fourth overflow valve 413, and the fourth check valve 416 is arranged on the pipeline connected with the T port of the fifth overflow valve 414. The third overflow valve 412 can prevent the oil circuit pressure from being too high due to the return oil circuit blockage, thereby damaging the hydraulic elements. The fourth overflow valve 413 and the fifth overflow valve 414 are respectively arranged on the front hydraulic motor and the rear hydraulic motor oil inlet circuits, and can prevent the oil circuit pressure from being too high due to the oil inlet circuit blockage or failure, thereby damaging the hydraulic elements. The third check valve 415 and the fourth check valve 416 can prevent the overflow valve from being damaged by the failure of the cleaning oil circuit.

[0130] The boom extension hydraulic system 501 and the boom bucket hydraulic system 502 in the above boom extension and bucket hydraulic system 500 have the same structure, and only the functions realized by the two are different, one realizes boom extension and the other realizes boom bucket. The structure of the boom extension hydraulic system 501 and the boom bucket hydraulic system 502 will be specifically described below by taking the boom extension hydraulic system 501 as an example. The boom extension hydraulic system 501 comprises a second three-position four-way hand-operated directional valve 503, a first adjustable throttle valve 504, a fifth check valve 505, a fourth direct-acting overflow valve 506, a third two-position two-way directional valve 507, a first safety overflow valve 508, a third single-piston rod hydraulic cylinder 509, a fourth single-piston rod hydraulic cylinder 510, a fourth two-position two-way directional valve 511, a fifth direct-acting overflow valve 512, a second adjustable throttle valve 513, a second safety overflow valve 514, a sixth check valve 515, a seventh check valve 516, an eighth check valve 517, and a second pipeline 518.

[0131] The P port of the second three-position four-way hand-operated directional valve 503 is connected with the main oil circuit, and the T port of the second three-position four-way hand-operated directional valve 503 is connected with the return oil circuit. The A port of the second three-position four-way hand-operated directional valve 503 is connected with the left oil chamber of the third single-piston rod hydraulic cylinder 509, and simultaneously connected with the left oil chamber of the fourth single-piston rod hydraulic cylinder 510. The B port of the second three-position four-way hand-operated directional valve 503 is connected with the right oil chamber of the third single-piston rod hydraulic cylinder 509, and simultaneously connected with the right oil chamber of the fourth single-piston rod hydraulic cylinder 510.

[0132] The second adjustable throttle valve 513 and the fourth two-position two-way directional valve 511 are arranged in sequence along the oil circuit direction (i.e. the direction from the second three-position four-way hand-operated directional valve 503 to the third single-piston rod hydraulic cylinder 509) on the pipeline connecting the A port of the second three-position four-way hand-operated directional valve 503 with the third single-piston rod hydraulic cylinder 509 and the fourth single-piston rod hydraulic cylinder 510. Specifically, the A port of the second adjustable throttle valve 513 is connected with the A port of the second three-position four-way hand-operated directional valve 503, the B port of the second adjustable throttle valve 513 is connected with the P port of the fourth two-position two-way directional valve 511, and the A port of the fourth two-position two-way directional valve 511 is connected with the left oil chamber of the third single-piston rod hydraulic cylinder 509 and simultaneously connected with the left oil chamber of the fourth single-piston rod hydraulic cylinder 510. The sixth check valve 515 is connected in parallel with the second adjustable throttle valve 513, and the sixth check valve 515 is the main hydraulic element through which the pressure oil passes when the sixth check valve 515 is the inlet oil circuit.

[0133] The first adjustable throttle valve 504, the third two-position two-way directional valve 507 are arranged in sequence on the pipeline connecting the B port of the second three-position four-way manual directional valve 503 and the third single piston rod hydraulic cylinder 509 and the fourth single piston rod hydraulic cylinder 510 along the oil path direction (i.e. the direction of the second three-position four-way manual directional valve 503 to the third single piston rod hydraulic cylinder 509). Specifically, the A port of the first adjustable throttle valve 504 is connected with the B port of the second three-position four-way manual directional valve 503, the B port of the first adjustable throttle valve 504 is connected with the P port of the third two-position two-way directional valve 507, the A port of the third two-position two-way directional valve 507 is connected with the right oil cavity of the third single piston rod hydraulic cylinder 509, and is also connected with the right oil cavity of the fourth single piston rod hydraulic cylinder 510. The fifth check valve 505 is connected in parallel with the first adjustable throttle valve 504, and the fifth check valve 505 is the main hydraulic element through which the pressure oil passes when the oil inlet pipeline.

[0134] The pipeline connected with the P port of the fourth two-position two-way directional valve 511 is connected with the pipeline connected with the P port of the third two-position two-way directional valve 507 through the second pipeline 518. The fifth direct-acting overflow valve 512 and the fourth direct-acting overflow valve 506 are arranged in sequence on the second pipeline 518 in the direction from the fourth two-position two-way directional valve 511 to the third two-position two-way directional valve 507, the fifth direct-acting overflow valve 512 is connected in parallel with the seventh check valve 516, and the fourth direct-acting overflow valve 506 is connected in parallel with the eighth check valve 517.

[0135] The P port of the above-mentioned first safety overflow valve 508 is connected with the right oil cavity of the fourth single piston rod hydraulic cylinder 510, and the T port of the first safety overflow valve 508 is connected with the oil return pipeline. The P port of the second safety overflow valve 514 is connected with the left oil cavity of the third single piston rod hydraulic cylinder 509, and the T port of the second safety overflow valve 514 is connected with the oil return pipeline.

[0136] In the present embodiment, the adjustable throttle valve 204 of the lifting circuit, the adjustable throttle valve 207 of the descending circuit, the second adjustable throttle valve 513 and the first adjustable throttle valve 504 can adjust the corresponding action speed of the large arm lifting, descending, stretching and bucket.

[0137] The present embodiment further comprises two filters 106, a hydraulic pump 107 and a heat dissipation fan 108, one filter 106 and the hydraulic pump 107 are arranged on the main oil pipeline, and the other filter 106 and the heat dissipation fan 108 are arranged on the oil return pipeline. The present embodiment further provides a working method of the hydraulic system of the small loader, which comprises the working method of the large arm lifting hydraulic system 200, the working method of the steering hydraulic system 300, the working method of the walking hydraulic system 400 and the working method of the large arm stretching and bucket hydraulic system 500, wherein:

[0138] The working method of the boom lifting hydraulic system 200 has four working conditions, as follows:

[0139] Working condition one, when the loader boom is normally lifted

[0140] When the first three-position four-way manual reversing valve 201 is connected to the left position, the A port and the P port of the first three-position four-way manual reversing valve 201 are communicated, and the B port and the T port are communicated. At this time, due to the operation of the hydraulic pump 107, the hydraulic oil is pumped out, causing the hydraulic control ports of the second two-position two-way reversing valve 205 and the first two-position two-way reversing valve 208 to sense pressure, pushing the spool of the second two-position two-way reversing valve 205 to the left and the spool of the first two-position two-way reversing valve 208 to the right, so that the second two-position two-way reversing valve 205 and the first two-position two-way reversing valve 208 are connected to the oil circuit.

[0141] The pressure oil flows from the P port of the first three-position four-way manual reversing valve 201 to the adjustable throttle valve 204 and the lifting circuit one-way valve 206 of the lifting circuit through the working oil port A, and then flows into the left oil chamber of the second single piston rod hydraulic cylinder 203 and the first single piston rod hydraulic cylinder 202 through the second two-position two-way reversing valve 205.

[0142] The oil in the right oil chamber of the second single piston rod hydraulic cylinder 203 and the first single piston rod hydraulic cylinder 202 flows through the first two-position two-way reversing valve 208 to the descending circuit adjustable throttle valve 207, and finally flows into the oil tank 100 through the B port of the first three-position four-way manual reversing valve 201.

[0143] Before the pistons of the second single piston rod hydraulic cylinder 203 and the first single piston rod hydraulic cylinder 202 move to the far right, i.e., before the boom reaches the maximum lifting height, the second one-way valve 213 and the first one-way valve 214 are not working.

[0144] Working condition two, when the boom is lifted to the maximum stroke, the hydraulic pump 107 is still supplying oil

[0145] When the second single piston rod hydraulic cylinder 203 and the first single piston rod hydraulic cylinder 202 move to the right end, and the operator still controls the boom to continue lifting, the hydraulic oil flows to the second overflow valve 211 through the second two-position two-way directional valve 205, and the pressure in the pipeline is higher than the set pressure of the second overflow valve 211, so the oil pushes the main valve core of the second overflow valve 211 to flow to the adjustable throttle valve 207 in the lowering circuit through the first check valve 214, and finally flows into the oil tank 100 through the B port of the first three-position four-way manual directional valve 201. At the same time, the solenoid of the second lever-controlled two-position two-way electromagnetic directional valve 218 is electrified to the left position, and the remote pressure regulating port of the lifting circuit safety overflow valve 217 is directly connected to the oil tank 100. At this time, because the pipeline pressure is greater than the set pressure of the remote pressure regulating port, the lifting circuit safety overflow valve 217 is discharged. In the second working condition, the second overflow valve 211 and the lifting circuit safety overflow valve 217 jointly discharge, forming a double safety overflow.

[0146] When the loader needs to maintain the current work

[0147] The first three-position four-way manual directional valve 201 is in the middle position, and the pressure oil flows in from the P port of the first three-position four-way manual directional valve 201 and directly returns to the oil tank 100 through the T port, at this time the hydraulic oil pressure is reduced. The second two-position two-way directional valve 205 senses that the pressure is insufficient to keep the valve core in the left position, and returns to the right position under the action of the spring. At this time, the pressure in the original pipeline is mainly borne by the second two-position two-way directional valve 205, and the first three-position four-way manual directional valve 201 does not directly bear the pressure of the second single piston rod hydraulic cylinder 203 and the first single piston rod hydraulic cylinder 202, but only bears the oil pressure in the original pipeline. If the second two-position two-way directional valve 205 fails to discharge, the first three-position four-way manual directional valve 201 can still ensure that the pipeline has a pressure maintaining function, and the second two-position two-way directional valve 205 and the first three-position four-way manual directional valve 201 form a double pressure maintaining function. And the first overflow valve 212, the first check valve 214, the second overflow valve 211 and the second check valve 213 can also ensure that the second two-position two-way directional valve 205 and the first three-position four-way manual directional valve 201 simultaneously fail to discharge to increase the pressure and cause cavitation.

[0148] When the loader fails to start due to failure

[0149] By manually adjusting the valve core of the second lever-controlled two-position two-way electromagnetic directional valve 218 to the right position, the lifting circuit safety overflow valve 217 is connected to the oil tank 100. At this time, because the pressure of the oil circuit connected to the P port of the lifting circuit safety overflow valve is higher than the set pressure of the remote pressure regulating port Y, the main valve core of the lifting circuit safety overflow valve 217 is lifted and discharged, and the boom falls for maintenance.

[0150] The specific operation of the boom lowering can be directly obtained by referring to the specific operation of the boom raising, and thus the specific operation steps of the boom lowering are omitted in the present application.

[0151] The working method of the steering hydraulic system 300 has five working conditions, which are as follows:

[0152] Working condition one, when the loader is straight driving

[0153] The steering valve group 302 is in the original position, the two-position four-way manual reversing valve 307 is connected to the right position, the second three-position four-way electromagnetic valve 308 is connected to the middle position, the pressure oil flows from the A port of the two-position four-way manual reversing valve 307, enters the B port, and then enters the P port of the second three-position four-way electromagnetic valve 308, and finally flows back to the tank 100 from the T port of the second three-position four-way electromagnetic valve 308.

[0154] The full hydraulic steering gear 301 does not work in the working condition one;

[0155] Working condition two, when the loader is left turning in the normal state

[0156] The two-position four-way manual reversing valve 307 is connected to the left position, the pressure oil flows from the P port of the two-position four-way manual reversing valve 307 to the A port and then enters the full hydraulic steering gear 301, at this time, the remote pressure sensing port of the second three-position four-way electromagnetic valve 308 controlled by the hydraulic pressure pushes the valve core to move right, the second three-position four-way electromagnetic valve 308 is connected to the right position, part of the pressure oil flows from the A port of the second three-position four-way electromagnetic valve 308 to the P port, flows into the B port of the two-position four-way manual reversing valve 307, flows out through the T port, and flows back to the tank 100, and the other part of the pressure oil flows from the B port of the second three-position four-way electromagnetic valve 308 to the T port and flows back to the tank 100; at this time, the first three-position four-way electromagnetic valve 304 is powered on the left side, pushes the valve core to move right, the first three-position four-way electromagnetic valve 304 is connected to the left position, the pressure oil enters from the P port of the first three-position four-way electromagnetic valve 304, flows to the B port, enters the left turning path synchronization valve group 310 through the left turning path one-way hydraulic control valve 306, and the pressure oil enters the upper cavity part of the left reciprocating double-piston rod hydraulic cylinder 311 and the lower cavity part of the right reciprocating double-piston rod hydraulic cylinder 312 at the same time, under the pushing of the pressure oil, the piston of the left reciprocating double-piston rod hydraulic cylinder 311 moves downward, the piston of the right reciprocating double-piston rod hydraulic cylinder 312 moves upward, and the loader turns left.

[0157] Working condition three, when the loader is left turning in an emergency

[0158] The two-position four-way manual reversing valve 307 remains in the original position, the pressure oil flows from the P port of the two-position four-way manual reversing valve 307 to the B port, and there is no pressure oil flowing through the oil path connected to the A port of the two-position four-way manual reversing valve 307, at this time, the remote pressure sensing port of the second three-position four-way electromagnetic valve 308 controlled by the hydraulic pressure does not work, and the valve core position of the second three-position four-way electromagnetic valve 308 is controlled by the manual lever;

[0159] When the loader is in the normal state and turns right, the second three-position four-way electromagnetic valve 308 is connected to the left position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve 307 to the P port of the second three-position four-way electromagnetic valve 308, then flows to the B port of the second three-position four-way electromagnetic valve 308, and then flows to the left turning road synchronous valve group 310; since it does not pass through the full hydraulic steering gear 301, the pressure loss is small, and the pressure oil simultaneously enters the upper cavity part of the left reciprocating double piston rod hydraulic cylinder 311 and the lower cavity part of the right reciprocating double piston rod hydraulic cylinder 312, the piston of the left reciprocating double piston rod hydraulic cylinder 311 moves rapidly downward, and the piston of the right reciprocating double piston rod hydraulic cylinder 312 moves rapidly upward, and the loader rapidly turns left.

[0160] When the loader is in the normal state and turns right, the second three-position four-way electromagnetic valve 308 is connected to the left position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve 307 to the P port of the second three-position four-way electromagnetic valve 308, then flows to the B port of the second three-position four-way electromagnetic valve 308, and then flows to the left turning road synchronous valve group 310; since it does not pass through the full hydraulic steering gear 301, the pressure loss is small, and the pressure oil simultaneously enters the upper cavity part of the left reciprocating double piston rod hydraulic cylinder 311 and the lower cavity part of the right reciprocating double piston rod hydraulic cylinder 312, the piston of the left reciprocating double piston rod hydraulic cylinder 311 moves rapidly downward, and the piston of the right reciprocating double piston rod hydraulic cylinder 312 moves rapidly upward, and the loader rapidly turns left.

[0161] When the loader is in the normal state and turns right, the second three-position four-way electromagnetic valve 308 is connected to the left position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve 307 to the P port of the second three-position four-way electromagnetic valve 308, then flows to the B port of the second three-position four-way electromagnetic valve 308, and then flows to the left turning road synchronous valve group 310; since it does not pass through the full hydraulic steering gear 301, the pressure loss is small, and the pressure oil simultaneously enters the upper cavity part of the left reciprocating double piston rod hydraulic cylinder 311 and the lower cavity part of the right reciprocating double piston rod hydraulic cylinder 312, the piston of the left reciprocating double piston rod hydraulic cylinder 311 moves rapidly downward, and the piston of the right reciprocating double piston rod hydraulic cylinder 312 moves rapidly upward, and the loader rapidly turns left.

[0162] When the loader is in the normal state and turns right, the second three-position four-way electromagnetic valve 308 is connected to the left position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve 307 to the P port of the second three-position four-way electromagnetic valve 308, then flows to the B port of the second three-position four-way electromagnetic valve 308, and then flows to the left turning road synchronous valve group 310; since it does not pass through the full hydraulic steering gear 301, the pressure loss is small, and the pressure oil simultaneously enters the upper cavity part of the left reciprocating double piston rod hydraulic cylinder 311 and the lower cavity part of the right reciprocating double piston rod hydraulic cylinder 312, the piston of the left reciprocating double piston rod hydraulic cylinder 311 moves rapidly downward, and the piston of the right reciprocating double piston rod hydraulic cylinder 312 moves rapidly upward, and the loader rapidly turns left.

[0163] When the loader is in the normal state and turns right, the second three-position four-way electromagnetic valve 308 is connected to the left position, and the pressure oil flows from the B port of the two-position four-way manual reversing valve 307 to the P port of the second three-position four-way electromagnetic valve 308, then flows to the B port of the second three-position four-way electromagnetic valve 308, and then flows to the left turning road synchronous valve group 310; since it does not pass through the full hydraulic steering gear 301, the pressure loss is small, and the pressure oil simultaneously enters the upper cavity part of the left reciprocating double piston rod hydraulic cylinder 311 and the lower cavity part of the right reciprocating double piston rod hydraulic cylinder 312, the piston of the left reciprocating double piston rod hydraulic cylinder 311 moves rapidly downward, and the piston of the right reciprocating double piston rod hydraulic cylinder 312 moves rapidly upward, and the loader rapidly turns left.

[0164] When the emergency right turn is made, the second three-position four-way electromagnetic valve (308) is connected to the right position, the pressure oil flows from the B port of the two-position four-way manual reversing valve (307) into the P port of the second three-position four-way electromagnetic valve (308), flows into the A port through the second three-position four-way electromagnetic valve (308), and then flows to the right turn road synchronous valve group (309); since it does not pass through the full hydraulic steering gear (301), the pressure loss is small, and the pressure oil simultaneously enters the lower cavity part of the left reciprocating double-piston rod hydraulic cylinder (311) and the upper cavity part of the right reciprocating double-piston rod hydraulic cylinder (312), the piston of the left reciprocating double-piston rod hydraulic cylinder (311) moves upward rapidly, the piston of the right reciprocating double-piston rod hydraulic cylinder (312) moves downward rapidly, and the loader rapidly turns right.

[0165] The working method of the above-mentioned walking hydraulic system 400 increases the flushing and cleaning mechanism compared with the existing walking hydraulic system, the flushing and cleaning mechanism is composed of a three-position three-way electromagnetic valve 411, a third overflow valve 412, a third one-way valve 415, and a fourth one-way valve 416, and does not work in the case of no electrical signal being connected. When the electrical signal is connected, the first four-position four-way electromagnetic valve 401 and the second four-position four-way electromagnetic valve 402 are both in the rightmost position, the three-position three-way electromagnetic valve 411 is connected to the left position or the right position, at this time, the hydraulic oil flushing pipeline corresponds to the cleaning upper section oil way and the cleaning lower section oil way respectively (the cleaning lower section oil way when connected to the left position, and the cleaning upper section oil way when connected to the right position). (In this application, the similar parts of the walking hydraulic system 400 and the existing walking hydraulic system are not described in detail.)

[0166] The hydraulic principle of the above-mentioned boom extension and bucket hydraulic system 500 is consistent with that of the boom lifting hydraulic system 200, and the boom extension and bucket hydraulic system 500 does not need the function of emergency pressure relief. Therefore, the working method of the boom extension and bucket hydraulic system 500 refers to the working method of the boom lifting hydraulic system 200.

[0167] In this embodiment, the whole machine hydraulic system is:

[0168] (1) Considering that the working pressure of the boom lifting hydraulic system 200 and the boom extension and bucket hydraulic system 500 is relatively high, which is significantly higher than that of the steering hydraulic system 300 and the walking hydraulic system 400, therefore, according to this working characteristic, a double-pump oil supply mode is adopted. The oil way of the system with high working pressure (i.e. the boom lifting hydraulic system 200 and the boom extension and bucket hydraulic system 500) is connected in parallel, and a high-pressure-resistant plunger pump is used for oil supply; the steering hydraulic system 300 and the walking hydraulic system 400 adopt a double-gear pump with strong stability, which can simultaneously supply oil to the walking and steering hydraulic systems.

[0169] (2) For the parallel part of the oil circuit (the main oil circuit connected by the hydraulic pump 107, the large arm lifting circuit 200, the large arm stretching and bucket hydraulic circuit 500), a multi-way valve (composed of a first two-position two-way electromagnetic reversing valve 101, two second two-position two-way electromagnetic reversing valves 103, and a first direct-acting overflow valve 102, a second direct-acting overflow valve 104, and a third direct-acting overflow valve 105) is specially designed to control the loader to perform large arm lifting, stretching, and bucket actions.

[0170] (3) The working principle of the multi-way valve is as follows: taking the large arm lifting action of the loader as an example, at this time, the first two-position two-way electromagnetic reversing valve 101 is connected to the initial position, and the two second two-position two-way electromagnetic reversing valves 103 are connected to the right position.

[0171] The present application comprehensively considers various possible situations in engineering practice, and optimizes the design of most systems. 1. In the large arm lifting hydraulic system 200, a double overflow safety valve group is designed, which can complete the work action when the large arm lifting or lowering reaches the limit, the reversing valve 205 and the first two-position two-way reversing valve 208 fail, and the hydraulic pump 107 fails to start. At the same time, it can also prevent the generation of cavitation phenomenon; in addition, by combining a reversing valve in the oil inlet, double pressure retention is realized when the loader large arm maintains action. 2. In the design of the steering hydraulic system, through the design of the steering valve group 302, the loader is successfully realized in the emergency situation. The rapid steering greatly improves the emergency obstacle avoidance ability of the loader. 3. In the design of the walking hydraulic mechanism, a cleaning device is added, which uses pressure oil to flush the pipeline to ensure the cleanliness of the pipeline. 4. In the design of the whole machine hydraulic system, a multi-way valve is designed to control the action. 5. On the oil supply strategy, according to different working characteristics, the hydraulic pump selection is optimized, and the plunger pump and the double gear pump are selected for different hydraulic systems to supply oil, which improves the efficiency and reliability.

[0172] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood as having meanings consistent with those in the prior art, and should not be interpreted with idealized or overly formal meanings unless otherwise defined.

[0173] The meaning of "and / or" described in the present application means that each single existence or both existences are included.

[0174] The meaning of "connection" described in the present application can be direct connection between components or indirect connection between components through other components.

[0175] With the above ideal embodiments according to the present application as the inspiration, through the above description, relevant staff can definitely make various changes and modifications without deviating from the scope of the technical idea of the present application. The technical scope of the present application is not limited to the content in the specification, and must be determined according to the scope of claims.

Claims

1. A hydraulic system for a small loader integrating pressure holding and safety overflow functions, comprising an oil tank (100), a main oil circuit, and a return oil circuit, wherein the main oil circuit is connected to the outlet end of the oil tank (100), and the return oil circuit is connected to the inlet end of the oil tank (100), characterized in that: The loader's hydraulic system includes a boom lifting hydraulic system (200), a steering hydraulic system (300), a travel hydraulic system (400), and a boom extension and bucket hydraulic system (500), wherein: The boom lifting hydraulic system (200), steering hydraulic system (300), travel hydraulic system (400), boom extension and bucket hydraulic system (500) all have their inlet end connected to the main oil circuit and their outlet end connected to the return oil circuit. A first two-position two-way solenoid directional valve (101) is installed on the main oil line between the boom lifting hydraulic system (200) and the oil tank (100). The connection status of the main oil line between the boom lifting hydraulic system (200) and the oil tank (100) is controlled by the first two-position two-way solenoid directional valve (101). The boom extension and bucket hydraulic system (500) includes a boom extension hydraulic system (501) and a boom bucket hydraulic system (502), both of which are connected to the oil tank (100) via the main oil circuit. A second two-position two-way solenoid directional valve (103) is installed on the main oil line between the boom extension hydraulic system (501) and the oil tank (100) and on the main oil line between the boom bucket hydraulic system (502) and the oil tank (100). The second two-position two-way solenoid directional valve (103) on the main oil line between the boom extension hydraulic system (501) and the oil tank (100) controls the connection state of the main oil line between the boom extension hydraulic system (501) and the oil tank (100). The second two-position two-way solenoid directional valve (103) on the main oil line between the boom bucket hydraulic system (502) and the oil tank (100) controls the connection state of the main oil line between the boom bucket hydraulic system (502) and the oil tank (100). The boom lifting hydraulic system (200) includes the boom lifting hydraulic system body and a dual safety relief valve assembly. The boom lifting hydraulic system body controls the lifting of the boom. The dual safety relief valve assembly is used to prevent cylinder blockage when the boom lifting hydraulic system body is in the working state of continuing to lift at the maximum stroke, and to prevent the oil circuit pressure from rising continuously, thus protecting the hydraulic components. The steering hydraulic system (300) includes a fully hydraulic steering gear (301), a steering valve assembly (302), and a synchronizing valve assembly (303). The pressure-holding function is achieved through the coordinated action of the fully hydraulic steering gear (301), the steering valve assembly (302), and the synchronizing valve assembly (303), wherein: The fully hydraulic steering gear (301) includes a first three-position four-way solenoid valve (304), a right-turn one-way hydraulic control valve (305), and a left-turn one-way hydraulic control valve (306), wherein: The A port of the first three-position four-way solenoid valve (304) is connected to the A port of the right turn one-way hydraulic control valve (305), the B port of the first three-position four-way solenoid valve (304) is connected to the A port of the left turn one-way hydraulic control valve (306), the P port of the first three-position four-way solenoid valve (304) is connected to the steering valve group (302), and the T port of the first three-position four-way solenoid valve (304) is connected to the return oil circuit. The B port of the right turn one-way hydraulic control valve (305) is connected to the steering valve group (302) and to the A port of the first throttle valve (313) and the second throttle valve (314). The X port of the right turn one-way hydraulic control valve (305) is connected to the B port of the first three-position four-way solenoid valve (304). The B port of the left-turn one-way hydraulic control valve (306) is connected to the steering valve assembly (302) and to the A ports of the third throttle valve (315) and the fourth throttle valve (316). The X port of the left-turn one-way hydraulic control valve (306) is connected to the A port of the first three-position four-way solenoid valve (304). The steering valve assembly (302) includes a two-position four-way manual directional valve (307) and a second three-position four-way solenoid valve (308), wherein: The P port of the two-position four-way manual directional valve (307) is connected to the main oil circuit, the T port of the two-position four-way manual directional valve (307) is connected to the return oil circuit, the A port of the two-position four-way manual directional valve (307) is connected to the P port of the first three-position four-way solenoid valve (304), and the A port of the two-position four-way manual directional valve (307) is connected to the remote control port of the second three-position four-way solenoid valve (308), and the B port of the two-position four-way manual directional valve (307) is connected to the P port of the second three-position four-way solenoid valve (308). The T port of the second three-position four-way solenoid valve (308) is connected to the return oil circuit, the A port of the second three-position four-way solenoid valve (308) is connected to the synchronization valve group (303), and the B port of the second three-position four-way solenoid valve (308) is connected to the synchronization valve group (303). Synchronization valve assembly (303) includes right-turn synchronization valve assembly (309), left-turn synchronization valve assembly (310), left-side reciprocating double piston rod hydraulic cylinder (311), and right-side reciprocating double piston rod hydraulic cylinder (312), wherein: The right-turn synchronous valve group (309) has a first throttle valve (313) and a second throttle valve (314) that operate synchronously. The A port of the first throttle valve (313) and the A port of the second throttle valve (314) are both connected to the A port of the second three-position four-way solenoid valve (308). The A port of the first throttle valve (313) and the A port of the second throttle valve (314) are both connected to the B port of the right-turn one-way hydraulic control valve (305). The B port of the first throttle valve (313) is connected to the lower oil chamber of the left reciprocating double piston rod hydraulic cylinder (311), and the B port of the second throttle valve (314) is connected to the upper oil chamber of the right reciprocating double piston rod hydraulic cylinder (312). The left-turn synchronous valve group (310) has a third throttle valve (315) and a fourth throttle valve (316) that operate synchronously. The A port of the third throttle valve (315) and the A port of the fourth throttle valve (316) are both connected to the B port of the second three-position four-way solenoid valve (308). The A port of the third throttle valve (315) and the A port of the fourth throttle valve (316) are both connected to the B port of the left-turn one-way hydraulic control valve (306). The B port of the third throttle valve (315) is connected to the lower oil chamber of the right reciprocating double piston rod hydraulic cylinder (312). The B port of the fourth throttle valve (316) is connected to the upper oil chamber of the left reciprocating double piston rod hydraulic cylinder (311).

2. The hydraulic system for a small loader with integrated pressure holding and safety overflow functions as described in claim 1, further characterized in that: the boom lifting hydraulic system body includes a first three-position four-way manual directional valve (201), a first single-piston rod hydraulic cylinder (202), a second single-piston rod hydraulic cylinder (203), a lifting circuit adjustable throttle valve (204), a second two-position two-way directional valve (205), a lifting circuit check valve (206), a lowering circuit adjustable throttle valve (207), a first two-position two-way directional valve (208), and a lowering circuit check valve (209), wherein: The P port of the first three-position four-way manual directional valve (201) is connected to the main oil circuit, the T port of the first three-position four-way manual directional valve (201) is connected to the return oil circuit, the A port of the first three-position four-way manual directional valve (201) is connected to the left oil chamber of the first single piston rod hydraulic cylinder (202), and the A port of the first three-position four-way manual directional valve (201) is connected to the left oil chamber of the second single piston rod hydraulic cylinder (203); the B port of the first three-position four-way manual directional valve (201) is connected to the right oil chamber of the first single piston rod hydraulic cylinder (202), and the B port of the first three-position four-way manual directional valve (201) is connected to the right oil chamber of the second single piston rod hydraulic cylinder (203); On the pipeline connecting the A port of the first three-position four-way manual directional valve (201) to the first single-piston rod hydraulic cylinder (202) and the second single-piston rod hydraulic cylinder (203), a lifting circuit adjustable throttle valve (204) and a second two-position two-way directional valve (205) are sequentially installed along the oil circuit direction. The lifting circuit check valve (206) is connected in parallel with the lifting circuit adjustable throttle valve (204); On the pipeline connecting the B port of the first three-position four-way manual directional valve (201) to the first single piston rod hydraulic cylinder (202) and the second single piston rod hydraulic cylinder (203), a descending circuit adjustable throttle valve (207) and a first two-position two-way directional valve (208) are sequentially installed along the oil circuit direction. The down-loop check valve (209) is connected in parallel with the down-loop adjustable throttle valve (207).

3. The small loader hydraulic system with integrated pressure holding and safety overflow functions according to claim 2, further characterized in that: The dual safety relief valve assembly includes a first pipeline (210), a second relief valve (211), a first relief valve (212), a second check valve (213), a first check valve (214), a descent circuit safety relief valve (215), a first lever-controlled two-position two-way solenoid directional valve (216), a lifting circuit safety relief valve (217), and a second lever-controlled two-position two-way solenoid directional valve (218), wherein: The pipe connected to the P port of the second two-position two-way reversing valve (205) is connected to the pipe connected to the P port of the first two-position two-way reversing valve (208) through the first pipe (210); A second relief valve (211) and a first relief valve (212) are sequentially arranged along the second two-position two-way directional valve (205) towards the first two-position two-way directional valve (208) on the first pipeline (210). The second relief valve (211) is connected in parallel with a second check valve (213), and the first relief valve (212) is connected in parallel with a first check valve (214). The right oil chambers of the first single piston rod hydraulic cylinder (202) and the second single piston rod hydraulic cylinder (203) are both connected to the P port of the descent circuit safety relief valve (215). The T port of the descent circuit safety relief valve (215) is connected to the return oil circuit. The Y port of the descent circuit safety relief valve (215) is connected to the P port of the first lever-controlled two-position two-way solenoid directional valve (216). The A port of the first lever-controlled two-position two-way solenoid directional valve (216) is connected to the return oil circuit. The left oil chambers of the first single-piston rod hydraulic cylinder (202) and the second single-piston rod hydraulic cylinder (203) are both connected to the P port of the lifting circuit safety relief valve (217). The T port of the lifting circuit safety relief valve (217) is connected to the return oil circuit. The Y port of the lifting circuit safety relief valve (217) is connected to the P port of the second lever-controlled two-position two-way solenoid directional valve (218). The A port of the second lever-controlled two-position two-way solenoid directional valve (218) is connected to the return oil circuit.

4. The hydraulic system for a small loader with integrated pressure holding and safety overflow functions according to claim 1, further characterized in that: it also includes a pump port overflow valve (317), a right turn overflow valve (318), and a left turn overflow valve (319), wherein: The P port of the pump outlet relief valve (317) is connected to the main oil circuit, and the T port of the pump outlet relief valve (317) is connected to the return oil circuit. The P port of the right turn relief valve (318) is connected to the pipeline between the right turn one-way hydraulic control valve (305) and the synchronous valve group (303), and the T port of the right turn relief valve (318) is connected to the return oil circuit. The P port of the left turn relief valve (319) is connected to the pipeline between the left turn one-way hydraulic control valve (306) and the synchronous valve group (303), and the T port of the left turn relief valve (319) is connected to the return oil circuit.

5. The hydraulic system for a small loader with integrated pressure holding and safety overflow functions according to claim 1, further characterized in that: the walking hydraulic system (400) includes a first four-position four-way solenoid valve (401), a second four-position four-way solenoid valve (402), a fifth throttle valve (403), a sixth throttle valve (404), a seventh throttle valve (405), an eighth throttle valve (406), a first hydraulic motor (407), a second hydraulic motor (408), a third hydraulic motor (409), a fourth hydraulic motor (410), a three-position three-way solenoid valve (411), a third overflow valve (412), a fourth overflow valve (413), a fifth overflow valve (414), a third check valve (415), and a fourth check valve (416), wherein: The P port of the first four-position four-way solenoid valve (401) is connected to the main oil circuit, and the T port of the first four-position four-way solenoid valve (401) is connected to the return oil circuit. The P port of the second four-position four-way solenoid valve (402) is connected to the main oil circuit, and the T port of the second four-position four-way solenoid valve (402) is connected to the return oil circuit. The A ports of the fifth throttle valve (403) and the sixth throttle valve (404) are both connected to the A port of the first four-position four-way solenoid valve (401). The B port of the fifth throttle valve (403) is connected to one end of the first hydraulic motor (407). The B port of the sixth throttle valve (404) is connected to one end of the second hydraulic motor (408). The other ends of the first hydraulic motor (407) and the other ends of the second hydraulic motor (408) are both connected to the B port of the first four-position four-way solenoid valve (401). The A ports of the seventh throttle valve (405) and the eighth throttle valve (406) are both connected to the A port of the second four-way solenoid valve (402). The B port of the seventh throttle valve (405) is connected to one end of the third hydraulic motor (409). The B port of the eighth throttle valve (406) is connected to one end of the fourth hydraulic motor (410). The other ends of the third hydraulic motor (409) and the other ends of the fourth hydraulic motor (410) are both connected to the B port of the second four-way solenoid valve (402). The P port of the three-position three-way solenoid valve (411) is connected to the main oil circuit, and the T port of the three-position three-way solenoid valve (411) is connected to the return oil circuit. The P port of the third relief valve (412) is connected to the A port of the three-position three-way solenoid valve (411), and the T port of the third relief valve (412) is connected to the return oil circuit. The P port of the fourth relief valve (413) is connected to the A port of the first four-position four-way solenoid valve (401), and the T port of the fourth relief valve (413) is connected to the return oil circuit. The P port of the fifth relief valve (414) is connected to the A port of the second four-position four-way solenoid valve (402), and the T port of the fifth relief valve (414) is connected to the return oil circuit. The third check valve (415) is installed on the pipe connected to the T port of the fourth relief valve (413); the fourth check valve (416) is installed on the pipe connected to the T port of the fifth relief valve (414).

6. The working method of the hydraulic system for a small loader with integrated pressure holding and safety overflow functions according to any one of claims 1 to 5, further characterized in that: it includes two filters (106), a hydraulic pump (107), and a cooling fan (108), one filter (106) and the hydraulic pump (107) are arranged on the main oil line, and the other filter (106) and the cooling fan (108) are arranged on the return oil line; The working methods of the hydraulic system of a small loader include the working methods of the boom lifting hydraulic system (200) and the steering hydraulic system (300), wherein: The boom lifting hydraulic system (200) has four operating conditions, as detailed below: Operating Condition 1: When the loader boom is raised normally The first three-position four-way manual directional valve (201) is connected to the left position. The A port of the first three-position four-way manual directional valve (201) is connected to the P port and the B port is connected to the T port. At this time, due to the operation of the hydraulic pump (107), hydraulic oil is pumped out, which causes the hydraulic control ports of the second two-position two-way directional valve (205) and the first two-position two-way directional valve (208) to sense the pressure, push the valve core of the second two-position two-way directional valve (205) to move to the left and push the valve core of the first two-position two-way directional valve (208) to move to the right, so that the second two-position two-way directional valve (205) and the first two-position two-way directional valve (208) are connected to the oil circuit. The pressurized oil flows from the P port of the first three-position four-way manual directional valve (201) through the working oil port A to the lifting circuit adjustable throttle valve (204) and the lifting circuit check valve (206), and then flows through the second two-position two-way directional valve (205) into the left oil chamber of the second single piston rod hydraulic cylinder (203) and the first single piston rod hydraulic cylinder (202); The oil in the right oil chambers of the second single piston rod hydraulic cylinder (203) and the first single piston rod hydraulic cylinder (202) flows through the first two-position two-way reversing valve (208), then flows to the adjustable throttle valve (207) of the descent circuit, and finally flows into the oil tank (100) through the B port of the first three-position four-way manual reversing valve (201). Before the pistons of the second single-piston rod hydraulic cylinder (203) and the first single-piston rod hydraulic cylinder (202) move to the rightmost end, that is, before the boom reaches the maximum lifting height, the second check valve (213) and the first check valve (214) do not work. Condition 2: When the boom is raised to its maximum stroke, the hydraulic pump (107) is still supplying oil. When the pistons of the second single-piston rod hydraulic cylinder (203) and the first single-piston rod hydraulic cylinder (202) move to the rightmost end, and the operator still controls the boom to continue lifting, the hydraulic oil flows through the second two-position two-way directional valve (205) to the second relief valve (211). At this time, the pressure in the pipeline is higher than the set pressure of the second relief valve (211). Therefore, the oil pushes the main valve core of the second relief valve (211) through the first check valve (214) to the adjustable throttle valve (207) of the descent circuit, and finally flows into the oil tank (100) through the B port of the first three-position four-way manual directional valve (201). At the same time, the electromagnet of the second lever-controlled two-position two-way solenoid directional valve (218) is energized and connected to the left position. The remote pressure regulating port of the lifting circuit safety relief valve (217) is directly connected to the oil tank (100). At this time, because the pipeline pressure is greater than the remote pressure regulating port setting pressure, the lifting circuit safety relief valve (217) leaks oil. Under operating condition two, the second relief valve (211) and the lifting circuit safety relief valve (217) jointly release oil, forming a double safety relief; Operating Condition 3: When the loader needs to maintain its current operation When the first three-position four-way manual directional valve (201) is in the neutral position, the pressure oil flows in from the P port of the first three-position four-way manual directional valve (201) and flows back directly to the oil tank (100) through the T port. At this time, the hydraulic oil circuit pressure decreases. The second two-position two-way directional valve (205) senses that the pressure is insufficient to push its valve core to remain in the left position. Under the action of the spring, it returns to the right position. At this time, the pressure in the original pipeline is mainly borne by the second two-position two-way directional valve (205). The first three-position four-way manual directional valve (201) does not directly bear the pressure of the second single piston rod hydraulic cylinder (203) and the first single piston rod hydraulic cylinder (202), but only bears the oil pressure in the original pipeline. If the second two-position two-way directional valve (205) leaks oil due to a malfunction, the first three-position four-way manual directional valve (201) can still ensure that the pipeline has a pressure-holding function. The second two-position two-way directional valve (205) and the first three-position four-way manual directional valve (201) form a double pressure-holding function. Furthermore, the first relief valve (212), the first check valve (214), the second relief valve (211), and the second check valve (213) can also ensure that the second two-position two-way directional valve (205) and the first three-position four-way manual directional valve (201) can simultaneously prevent cavitation caused by increased oil leakage due to failure, resulting in a sudden drop in pressure. Operating Condition 4: When the loader fails to start due to a malfunction By manually adjusting the valve core of the second lever-controlled two-position two-way solenoid directional valve (218) to the right position, the lifting circuit safety relief valve (217) is connected to the oil tank (100). At this time, because the oil pressure connected to the P port of the lifting circuit safety relief valve (217) is higher than the set pressure at the remote pressure regulating port Y, the main valve core of the lifting circuit safety relief valve (217) is raised to drain oil, and the boom is lowered for maintenance. The steering hydraulic system (300) operates in five modes, as follows: Operating Condition 1: When the loader is traveling in a straight line The steering valve assembly (302) is in its original position, the two-position four-way manual directional valve (307) is connected to the right position, and the second and third-position four-way solenoid valve (308) is connected to the middle position. The pressure oil flows in from port A of the two-position four-way manual directional valve (307), passes through port B to port P of the second and third-position four-way solenoid valve (308), and finally flows back to the oil tank (100) from port T of the second and third-position four-way solenoid valve (308). Under normal operating conditions, the fully hydraulic steering gear (301) does not work; Operating Condition 2: When the loader turns left under normal conditions When the two-position four-way manual directional valve (307) is in the left position, the pressurized oil flows from port P of the two-position four-way manual directional valve (307) into port A and then into the fully hydraulic steering gear (301). At this time, the remote pressure regulating port of the hydraulically controlled second-position four-way solenoid valve (308) senses the pressure and pushes the valve core to the right. The second-position four-way solenoid valve (308) is in the right position. Part of the pressurized oil flows from port A of the second-position four-way solenoid valve (308) to port P, then flows into port B of the two-position four-way manual directional valve (307) and flows out through port T. The other part flows into port B of the second-position four-way solenoid valve (308) and flows out through port T, and both flow back to the oil tank (100). When the left side of the first three-position four-way solenoid valve (304) is energized, the valve core is pushed to the right and the first three-position four-way solenoid valve (304) is in the left position. The pressure oil enters from the P port of the first three-position four-way solenoid valve (304), flows to the B port, and enters the left turn synchronous valve group (310) through the left turn one-way hydraulic control valve (306). The pressure oil simultaneously enters the upper chamber of the left reciprocating double piston rod hydraulic cylinder (311) and the lower chamber of the right reciprocating double piston rod hydraulic cylinder (312). Under the push of the pressure oil, the piston of the left reciprocating double piston rod hydraulic cylinder (311) moves downward and the piston of the right reciprocating double piston rod hydraulic cylinder (312) moves upward, and the loader turns to the left. Working condition 3: When the loader turns left in an emergency The two-position four-way manual directional valve (307) remains in its original position. The pressure oil flows from port P to port B of the two-position four-way manual directional valve (307). No pressure oil flows through the oil circuit connected to port A of the two-position four-way manual directional valve (307). At this time, the remote pressure regulating port of the hydraulically controlled second three-position four-way solenoid valve (308) does not work. The valve core position of the second three-position four-way solenoid valve (308) is controlled by the manual lever. When making an emergency left turn, the second and third position four-way solenoid valve (308) is in the left position. The pressure oil flows from the B port of the two-position four-way manual directional valve (307) into the P port of the second and third position four-way solenoid valve (308), then flows through the second and third position four-way solenoid valve (308) into the B port, and then flows to the left turn synchronous valve group (310). Since it does not pass through the full hydraulic steering gear (301), the pressure loss is small. The pressure oil simultaneously enters the upper chamber of the left reciprocating double piston rod hydraulic cylinder (311) and the lower chamber of the right reciprocating double piston rod hydraulic cylinder (312). The piston of the left reciprocating double piston rod hydraulic cylinder (311) moves downward rapidly, and the piston of the right reciprocating double piston rod hydraulic cylinder (312) moves upward rapidly, and the loader turns left rapidly. Operating Condition 4: When the loader turns right under normal conditions When the two-position four-way manual directional valve (307) is in the left position, the pressurized oil flows from port P of the two-position four-way manual directional valve (307) into port A and then into the fully hydraulic steering gear (301). At this time, the remote pressure regulating port of the hydraulically controlled second-position four-way solenoid valve (308) senses the pressure and pushes the valve core to the left. The second-position four-way solenoid valve (308) is in the right position. Part of the pressurized oil flows from port A of the second-position four-way solenoid valve (308) to port P, then flows into port B of the two-position four-way manual directional valve (307) and flows out through port T. The other part flows into port B of the second-position four-way solenoid valve (308) and flows out through port T, and both flow back to the oil tank (100). When the right side of the first three-position four-way solenoid valve (304) is energized, the valve core is pushed to the right and the first three-position four-way solenoid valve (304) is in the right position. The pressure oil enters from the P port of the first three-position four-way solenoid valve (304), flows to the A port, and enters the right turn synchronous valve group (309) through the right turn one-way hydraulic control valve (305). The pressure oil simultaneously enters the lower chamber of the left reciprocating double piston rod hydraulic cylinder (311) and the upper chamber of the right reciprocating double piston rod hydraulic cylinder (312). Under the push of the pressure oil, the piston of the left reciprocating double piston rod hydraulic cylinder (311) moves upward and the piston of the right reciprocating double piston rod hydraulic cylinder (312) moves downward, and the loader turns to the right. Condition 5: When the loader turns right in an emergency The two-position four-way manual directional valve (307) remains in its original position. The pressure oil flows from port P to port B of the two-position four-way manual directional valve (307). No pressure oil flows through the oil circuit connected to port A of the two-position four-way manual directional valve (307). At this time, the remote pressure regulating port of the hydraulically controlled second three-position four-way solenoid valve (308) does not work. The valve core position of the second three-position four-way solenoid valve (308) is controlled by the manual lever. When making an emergency right turn, the second and third position four-way solenoid valve (308) is in the right position. The pressure oil flows from port B of the two-position four-way manual directional valve (307) into port P of the second and third position four-way solenoid valve (308), then flows through port A of the second and third position four-way solenoid valve (308), and then flows to the right turn synchronization valve group (309). Since it does not pass through the full hydraulic steering gear (301), the pressure loss is small. The pressure oil simultaneously enters the lower chamber of the left reciprocating double piston rod hydraulic cylinder (311) and the upper chamber of the right reciprocating double piston rod hydraulic cylinder (312). The piston of the left reciprocating double piston rod hydraulic cylinder (311) moves upward rapidly, and the piston of the right reciprocating double piston rod hydraulic cylinder (312) moves downward rapidly, and the loader turns right rapidly.

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