CN213475269U - Safety device of lifting system and tractor - Google Patents

Abstract

The utility model relates to a lifting device discloses a safety device of lifting system, include hydraulic pump (2), lift valve (3), operating valve (4) and air pressure switch (5) of being connected with motor (1), hydraulic pump (2) are passed through lift valve (3) are connected with lift cylinder (6), operating valve (4) through first gas circuit (71) and second gas circuit (72) with two spring control chambeies of lift valve (3) are connected respectively, air pressure switch (5) are located on first gas circuit (71) and second gas circuit (72), in order to control the switching-over of lift valve (3), air pressure switch (5) with motor (1) are established ties, in order to control opening of motor (1) stops. The utility model also discloses a tractor. The utility model discloses a safety device of system of lifting can control opening and close of motor, prevents to forget to close the motor and leads to the system to damage.

Description

Safety device of lifting system and tractor

Technical Field

The present invention relates to lifting devices, and more particularly, to a safety device for a lifting system; the invention also relates to a tractor with the safety device of the lifting system.

Background

With the rapid development of economy in China and the great investment of China in highway construction, highway transportation has become a main transportation mode in China. The tractor serves as main equipment for road transportation and is widely applied due to the advantages of strong specialization, large loading capacity and quick transportation. The tractor is a common large truck or semi-trailer which is towed by tools between a truck head and a truck bed, namely, the truck head can be separated from the original truck bed to tow other truck beds, and the truck bed can also be separated from the original truck head to be towed by other truck heads. The front of the trailer is provided with a driving capability to call a tractor, and the rear of the trailer is provided with a trailer without the driving capability, and the trailer is dragged away by the tractor. The connection mode of the tractor and the trailer has two types: the first is that the front half of the trailer is put on a traction saddle above the rear section of the tractor, and the bridge behind the tractor bears a part of the weight of the trailer, namely the semitrailer; the second is that the front end of the trailer is connected to the rear end of the tractor, and the tractor only provides forward pulling force to drag the trailer, but does not bear the downward weight of the trailer, and the trailer is fully hung. Are often used for the transportation of bulk goods within or between workshops, such as the transportation of car manufacturing warehouses to assembly lines, baggage transportation at airports.

Chinese utility model patent application with application number CN201721415522.3 discloses a hydraulic lifting device and tractor, wherein, hydraulic lifting device includes oil tank, hydraulic pump, switching-over valve, one-way throttle valve and lifts the top cylinder. The reversing valve is a three-position four-way valve, the one-way throttle valve comprises a one-way valve and a throttle valve which are connected in parallel, the lifting top cylinder comprises a rodless cavity and a rod cavity, the input end of a hydraulic pump is connected with an oil tank through an oil suction pipe, the output end of the hydraulic pump is connected with a P port of the three-position four-way valve through a high-pressure oil pipe, a T port of the three-position four-way valve is connected with the oil tank through an oil return pipe, the one-way throttle valve is arranged between an A port of the three-position four-way valve and the rodless cavity of the lifting top cylinder, the A port of the three-position four-way valve is connected with the input end of the one-way valve in the one-way throttle valve, the output end of the one-way valve in the one-way throttle valve is connected with the rodless cavity of the lifting.

The hydraulic lifting device works by taking power from the motor, and after the lifting system finishes working, if the motor is forgotten to be turned off, the system continuously operates, and the system is damaged by oil temperature rising.

In view of the above, there is a need to design a new safety device for a lifting system, which can overcome or alleviate the above technical problems.

SUMMERY OF THE UTILITY MODEL

The utility model aims to solve the technical problem that a safety device of system lifts is provided, this safety device of system lifts can control opening and close of motor, prevents to forget to close the motor and leads to the system damage.

The utility model aims to solve the technical problem that a tractor is provided, this tractor has better security performance.

In order to solve the technical problem, the utility model provides a safety device of lifting system, include the hydraulic pump of being connected with the motor, lift valve, control valve and baroswitch, the hydraulic pump passes through lift valve is connected with the lift hydro-cylinder, the control valve through first gas circuit and second gas circuit with two spring control chambeies of lift valve are connected respectively, the baroswitch is located on first gas circuit and the second gas circuit, in order to control the switching-over of lift valve, the baroswitch with the motor is established ties, in order to control opening of motor stops.

Preferably, the lift valve includes a first oil port connected to the hydraulic pump through an oil inlet path, a second oil port connected to an oil return path, a third oil port connected to a rodless cavity of the lift cylinder, and a fourth oil port connected to a rod cavity of the lift cylinder.

Specifically, a third oil port of the lifting valve is connected with a rodless cavity of the lifting oil cylinder through a balance valve, and a control end of the balance valve is connected with a rod cavity of the lifting oil cylinder.

More specifically, the fourth port of the lift valve is connected to the oil return path through a throttle valve.

Typically, a filter is arranged on the oil return path, and an oil return one-way valve is connected in parallel on the filter so as to enable the hydraulic oil to be introduced into the oil tank in one direction; and the oil inlet oil way is provided with an oil inlet one-way valve so as to enable the hydraulic oil flowing out of the hydraulic pump to be led into the lifting valve in a single direction.

Specifically, an overflow valve is arranged between the oil inlet oil way and the oil return oil way.

Preferably, the operating valve is a pneumatic reversing valve, and the pneumatic reversing valve comprises an air inlet, a first working air port connected with the first air path, a second working air port connected with the second air path and an air outlet.

Specifically, an explosion-proof valve is arranged on an oil path between a rodless cavity of the lifting oil cylinder and the lifting valve.

Typically, an electrical switch is arranged on a circuit between the air pressure switch and the motor.

The utility model also discloses a tractor, including any one of the above-mentioned technical scheme safety device of lifting system.

Through the technical scheme, the beneficial effects of the utility model are as follows:

in the basic technical scheme of the utility model, the air pressure switches are skillfully arranged on the first air circuit and the second air circuit, and the air pressure switches can be closed by sensing the air pressure through the control valve, so that the motor is electrified to operate, and meanwhile, the lifting valve is controlled to change direction, thereby realizing the lifting of the lifting oil cylinder; the air pressure switch can be disconnected due to the fact that the air pressure switch cannot sense air pressure, so that the motor is powered off and stops working, and the situation that the system is damaged due to the fact that an operator forgets to turn off the motor or the habit of turning off the motor is avoided.

Other features and more prominent advantages of the invention will be described in detail in the detailed description that follows.

Drawings

The accompanying drawings, which form a part hereof, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without undue limitation. In the drawings:

fig. 1 is a hydraulic schematic diagram of a safety device of a lifting system according to an embodiment of the present invention.

Description of the reference numerals

1 motor 2 hydraulic pump

3 lifting valve A1 first oil port of lifting valve

Second port of A2 Lift valve third port of A3 Lift valve

Fourth port 4 operating valve of A4 lifting valve

Air inlet of B1 pneumatic reversing valve B2 first working air port of pneumatic reversing valve

Second working air port B4 of B3 pneumatic reversing valve

5 pneumatic switch 6 lifting oil cylinder

71 first air path 72 second air path

81 oil inlet path 82 oil return path

91 balanced valve 92 throttle valve

93 filter 94 oil return one-way valve

96 oil inlet check valve of 95 overflow valve

97 explosion-proof valve 98 electric switch

Detailed Description

The following describes in detail embodiments of the present invention with reference to the accompanying drawings. It is to be understood that the description of the embodiments herein is for purposes of illustration and explanation only and is not intended to limit the invention.

Furthermore, the terms "first", "second", "third", "fourth" are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated, and therefore the features defined as "first", "second", "third", "fourth" may explicitly or implicitly include one or more of the features described.

In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "disposed," and "connected" are to be construed broadly, and may include, for example, a fixed connection, a detachable connection, or an integral connection; either directly or indirectly through intervening media, either internally or in any combination thereof. The specific meaning of the above terms in the present invention can be understood according to specific situations by those skilled in the art.

First, it should be noted that, for those skilled in the art, after knowing the technical idea of the hydraulic connection relationship of the present invention, the oil circuit or the valve can be simply replaced, so as to realize the function of the safety device of the lifting system of the present invention, which also belongs to the protection scope of the present invention. The related hydraulic components, such as the reversing valve, the overflow valve, the check valve, the throttle valve, the motor, the hydraulic pump, the pneumatic valve, etc., are well known to those skilled in the art and are commonly used in the existing hydraulic system, so that the hydraulic components will be only briefly described below, and the description will focus on the original hydraulic connection relationship of the safety device of the lifting system of the present invention.

As shown in fig. 1, the utility model discloses basic embodiment's lifting system's safety device, include the hydraulic pump 2 of being connected with motor 1, lift valve 3, operating valve 4 and baroswitch 5, hydraulic pump 2 is connected with lift cylinder 6 through lifting valve 3, operating valve 4 is connected respectively with two spring control chambeies of lifting valve 3 through first gas circuit 71 and second gas circuit 72, baroswitch 5 is located first gas circuit 71 and second gas circuit 72, with the switching-over that can control lift valve 3, baroswitch 5 establishes ties with motor 1, with the start-stop that can control motor 1.

The existing hydraulic lifting device can well operate the lifting of the lifting jacking cylinder through the three-position four-way valve, but after the lifting system finishes working, if an operator forgets to close the motor or does not have the habit of closing the motor, the system can continuously run to increase the oil temperature, so that the system is damaged.

The safety device of the lifting system of the utility model skillfully arranges the air pressure switch 5 on the air control pipeline of the lifting valve 3, the air control pipeline is a first air circuit 71 and a second air circuit 72, moreover, the air pressure switch 5 is also connected with the motor 1 in series, the control valve 4 is connected with the air pressure switch 5 through the first air circuit 71 and the second air circuit 72, and the air pressure switch 5 can be closed or disconnected without sensing the air pressure through the switching of the control valve 4, thereby controlling the starting and stopping of the motor 1; this kind of gas circuit cooperation relation realizes the control to motor 1 through simple connected mode, can effectively solve operating personnel and forget the problem of closing motor 1 or not closing the habit of motor 1, and operating personnel only need according to conventional operation, after lifting the system and finishing work, makes operating valve 4 be in the meso position, just can avoid motor 1 continuous operation to arouse that the oil temperature rises and cause the damage of system. When the pneumatic switch 5 is in the closed state, the control valve 4 can control the lifting valve 3 to switch through the first air passage 71 and the second air passage 72 which are respectively connected with the two spring control chambers of the lifting valve 3, and the control on the lifting of the lifting oil cylinder 6 is not influenced.

In a specific embodiment, the lifting valve 3 is preferably a three-position four-way valve, and may include a first oil port a1, a second oil port a2, a third oil port A3, and a fourth oil port a4, the first oil port a1 of the lifting valve 3 is connected to the hydraulic pump 2 through an oil inlet path 81, the second oil port a2 of the lifting valve 3 is connected to the oil tank through an oil return path 82, the third oil port A3 of the lifting valve 3 is connected to a rodless cavity of the lifting cylinder 6, the fourth oil port a4 of the lifting valve 3 is connected to a rod cavity of the lifting cylinder 6, spring control cavities at two ends of the lifting valve 3 are connected to the control valve 4 through a first air passage 71 and a second air passage 72, and the first air passage 71 and the second air passage 72 are connected in series to the air pressure switch 5; when the control valve 4 makes the air pressure switch 5 close by sensing air pressure, and the circuit is switched on, the motor 1 can drive the hydraulic pump 2 to operate, the control valve 4 can control the lifting valve 3, when the lifting valve 3 is in the right position, the hydraulic pump 2 supplies oil to the rodless cavity of the lifting oil cylinder 6 through the first oil port A1 and the third oil port A3 of the lifting valve 3, hydraulic oil in the rod cavity of the lifting oil cylinder 6 flows back to the oil tank through the fourth oil port A4 and the second oil port A2 of the lifting valve 3, and the lifting oil cylinder 6 performs lifting movement; when the lifting valve 3 is in the left position, the hydraulic pump 2 supplies oil to the rod cavity of the lifting oil cylinder 6 through the first oil port a1 and the fourth oil port a4 of the lifting valve 3, hydraulic oil in the rodless cavity of the lifting oil cylinder 6 flows back to the oil tank through the third oil port A3 and the second oil port a2 of the lifting valve 3, and the lifting oil cylinder 6 performs descending motion; when the air pressure switch 5 is turned off by the operation valve 4 without sensing the air pressure, the first air passage 71 and the second air passage 72 are cut off, the electric circuit is also cut off, the motor 1 is powered off and stops operating, accordingly, the hydraulic pump 2 stops operating, and the lift valve 3 returns to the neutral position. Of course, the lifting valve 3 may also be other pneumatic control valves capable of achieving the same function, for example, the lifting valve 3 may be a three-position three-way valve, and correspondingly, the lifting cylinder 6 may be a telescopic cylinder, and a working oil port of the three-position three-way valve is connected to the telescopic cylinder, so as to supply oil to the telescopic rod or return oil from the telescopic cylinder to the working oil port of the three-position three-way valve. Among them, the hydraulic pump 2 is preferably a gear pump.

Wherein, install oil feed check valve 96 on the oil feed oil circuit 81, can make the hydraulic oil one-way flow direction of hydraulic pump 2 output lift valve 3, prevent that hydraulic oil backward flow from hydraulic pump 2.

In addition, an electrical switch 98 is arranged on a circuit between the air pressure switch 5 and the motor 1, and the electrical switch 98 is used as a lead-in switch of a power supply, and the type is various, such as a combination switch, a rocker switch and the like.

Further, a balance valve 91 is arranged between the lifting valve 3 and the lifting oil cylinder 6, specifically, a third oil port a3 of the lifting valve 3 is connected with a rodless cavity of the lifting oil cylinder 6 through the balance valve 91, a control end of the balance valve 91 is connected with a rod cavity of the lifting oil cylinder 6, and the balance valve 91 can balance hydraulic oil pressure of a pipeline between the rod cavity of the lifting oil cylinder 6 and the rodless cavity of the rod cavity, so that the lifting oil cylinder 6 is prevented from stalling and pressure loss, the load is stably lowered, and impact vibration is small.

The fourth port a4 of the lift valve 3 is also connected to the oil return passage 82, and a throttle 92 is installed between the fourth port a4 of the lift valve 3 and the oil return passage 82; the hydraulic oil pressure in the pipeline is prevented from being overlarge, a part of hydraulic oil is shunted and flows to the oil tank through the throttle valve 92, the system safety is guaranteed, and the throttle valve can form back pressure, so that the load is stably reduced.

In order to adjust the oil supply pressure and prevent overload, an overflow valve 95 is arranged between the oil inlet path 81 and the oil return path 82, and the input end of the overflow valve is connected with the output end of the hydraulic pump 2 so as to effectively adjust the pressure.

In order to prevent the oil from being polluted, keep the oil clean and ensure the normal operation of the system, a filter 93 can be arranged on the oil return oil way 82, so that the hydraulic oil flows back to the oil tank after being filtered by the filter 93; furthermore, a return check valve 94 may be connected in parallel to the filter 93 to enable hydraulic oil to be introduced into the oil tank in one direction, so as to prevent the filter 93 from being blocked and affecting return oil.

In the specific example shown in fig. 1, the number of the lifting cylinders 6 is two, the rodless cavities of the two lifting cylinders 6 are connected and then connected to the third port A3 of the lifting valve 3, and the rod cavities of the two lifting cylinders 6 are connected and then connected to the fourth port a4 of the lifting valve 3; moreover, the anti-explosion valves 97 are installed on the pipelines outside the rodless cavities of the two lifting oil cylinders 6, and the anti-explosion valves 97 are connected with the third oil port A3 of the lifting valve 3 through the balance valve 91; when a fault occurs, the anti-explosion valve 97 can block an oil way, prevent the lifting oil cylinder 6 from suddenly dropping due to the pressure loss of oil, and have better safety.

As a specific embodiment, the operation valve 4 is a pneumatic directional control valve, and specifically, a three-position four-way valve may be used, and the pneumatic directional control valve includes an air inlet B1, a first working air port B2, a second working air port B3 and an air outlet B4, the first working air port B2 of the pneumatic directional control valve is connected to the first air channel 71, and the second working air port B3 of the pneumatic directional control valve is connected to the second air channel 72. When the control valve 4 is in the right position function, the air source is communicated with the first air path 71 through the air inlet B1 and the first working air port B2 of the pneumatic reversing valve, so that the lifting valve 3 is in the right position function, and at the moment, the hydraulic pump 2 supplies oil to a rodless cavity of the lifting oil cylinder 6 through the lifting valve 3 to drive the hydraulic oil cylinder 6 to do lifting motion; when the control valve 4 is in the left position function, the air source is communicated with the second air path 72 through the air inlet B1 and the second working air port B3 of the pneumatic reversing valve, so that the air pressure switch 5 is closed, air is injected into the spring control cavity of the lifting valve 3, the lifting valve 3 is in the left position function, the rodless cavity of the hydraulic oil cylinder 6 is communicated with the oil return path 82, and the hydraulic oil cylinder 6 performs the descending action; when the pilot valve 4 is in the neutral position function, both the first air passage 71 and the second air passage 72 are communicated with the atmosphere through the exhaust port B4 of the pilot valve 4, so that the lift valve 3 is also in the neutral position function, and the first oil port a1 of the lift valve 3 is communicated with the second oil port a2 thereof, that is, the hydraulic pump 2 is communicated with the oil return passage.

It should be noted that the operation valve 4 may also be other pneumatic directional valves capable of implementing the same function, such as a three-position five-way valve, which plugs a valve port of the three-position five-way valve, and may also implement the same function as the three-position four-way valve. In addition, the operating valve 4 is preferably a handle type pneumatic reversing valve, and through the operating handle, to accomplish each item of operation, other modes can also be adopted to control the operating valve 4, such as electric control mode, hydraulic control mode, etc.

In order to facilitate a more profound understanding of the technical idea and advantages of the safety device of the lifting system according to the invention, a relatively preferred feature and a relatively comprehensive construction according to the invention are described below with reference to fig. 1.

As shown in fig. 1, the safety device of a lifting system according to a preferred embodiment of the present invention includes a hydraulic pump 2, a lifting valve 3, a control valve 4 and a pneumatic switch 5, the hydraulic pump 2 is connected to a motor 1, the motor 1 can drive the hydraulic pump 2 to operate, and a ball valve is disposed between the hydraulic pump 2 and an oil tank to control the on-off between the hydraulic pump 2 and the oil tank; the air pressure switch 5 is connected with the motor 1 in series, the starting and the stopping of the motor 1 can be controlled, and a rocker switch is arranged between the air pressure switch 5 and the motor 1 to introduce a power supply; the first oil port A1 of the lifting valve 3 is connected with the hydraulic pump 2 through the oil inlet oil way 81, the oil inlet check valve 96 is installed on the oil inlet oil way 81, the second oil port A2 of the lifting valve 3 is connected with the oil tank through the oil return way 82, the oil return way 82 is provided with a filter 93, and the filter 93 is connected with the oil return check valve 94 in parallel; the third oil port A3 of the lifting valve 3 is connected with a rodless cavity of the lifting oil cylinder 6, the fourth oil port A4 of the lifting valve 3 is connected with a rod cavity of the lifting oil cylinder 6, the third oil port A3 of the lifting valve 3 is connected with the rodless cavity of the lifting oil cylinder 6 through a balance valve 91, the control end of the balance valve 91 is connected with the rod cavity of the lifting oil cylinder 6, the rodless cavity of the lifting oil cylinder 6 is connected with the balance valve 91 through an explosion-proof valve 97, and the fourth oil port A4 of the lifting valve 3 is connected with the oil return circuit 82 through a throttle valve 92; the spring control cavities at two ends of the lifting valve 3 are respectively connected with the first air path 71 and the second air path 72, and the first air path 71 and the second air path 72 are correspondingly connected with the first working air port B2 and the second working air port B3 of the operating valve 4 through the air pressure switch 5.

The operating valve 4 is preferably of a handle type, an operator operates the handle to enable an air source to respectively act on spring control cavities at two ends of the lifting valve 3 through the operating valve 4 to control lifting of the lifting oil cylinder 6, meanwhile, the air pressure switch 5 is installed on the first air path 71 and the second air path 72, and the air pressure switch 5 is closed and opened to control running of the motor 1, so that running of the hydraulic pump 2 is controlled, and the situation that the operator forgets to close the motor 1 or the system is continuously heated to damage the system due to the fact that the habit of not closing the motor 1 is avoided is effectively prevented.

The working process of the safety device of the lifting system of the present invention is further described below in order to better understand the technical idea of the present invention.

When the lifting valve 4 is in a right position function, the air pressure switch 5 is closed by sensing air pressure, so that the motor 1 is powered on, the hydraulic pump 2 is driven to operate, an air source is communicated with the first air passage 71 through the air inlet B1 and the first working air port B2 of the control valve 4, the lifting valve 3 is in the right position function, the first oil port A1 of the lifting valve 3 is communicated with the third oil port A3 of the lifting valve 3, the hydraulic pump 2 supplies oil to a rodless cavity of the lifting oil cylinder 6 through the first oil port A1 and the third oil port A3 of the lifting valve 3, and the hydraulic oil cylinder 6 is driven to perform lifting motion;

when the hydraulic pump is stopped, the operating valve 4 is positioned in a neutral position function, the air pressure switch 5 is in a disconnected state because the air pressure can not be sensed, the motor 3 is not connected, and the hydraulic pump 2 does not run and generates heat;

when the hydraulic lifting valve 3 is in the left position, the operating valve 4 is positioned in the left position to function, the air pressure switch 5 is closed by sensing air pressure, the motor 1 is powered on, the hydraulic pump 2 is driven to operate, an air source is communicated with the second air passage 72 through the air inlet B1 and the second working air port B3 of the operating valve 4, air is injected into the spring control cavity of the lifting valve 3 to enable the lifting valve 3 to be in the left position, the third oil port A3 of the lifting valve 3 is communicated with the second oil port A2 of the lifting valve 3, the rodless cavity of the hydraulic oil cylinder 6 is communicated with the oil return oil passage 82 through the third oil port A3 and the second oil port A2 of the lifting valve 3, and the hydraulic oil cylinder 6 is enabled to do the descending motion; after the hydraulic oil cylinder 6 descends to the right position, the operating valve 4 is only required to return to the middle position, the air passage is disconnected, the air pressure switch 5 is disconnected due to the fact that pressure cannot be sensed, the motor 1 is powered off and stops working, and the situation that the system is damaged due to the fact that an operator forgets to turn off the motor 1 or the habit of turning off the motor 1 causes the continuous temperature rise of the system can be prevented.

According to the above working process, the utility model discloses no complicated gas circuit cooperation relation only needs to increase an atmospheric pressure switch 5, simple structure, and convenient operation only needs to make the operating valve 4 be in the meso position, just can close the motor through atmospheric pressure switch 5, effectively avoids because the oil temperature continuously rises and the damage of the hydraulic pump oil blanket that causes, takes place the phenomenon that the hydraulic pump burns out even, causes the system damage.

Besides, in addition to the above-mentioned manner of controlling the motor 1 by using the air pressure switch 5, a controller may be used to control the operation time of the motor 1 in combination with a program, for example, the motor 1 is automatically turned off after a set time is exceeded, and the automatic control of the motor 1 can be realized to achieve the technical effect of preventing the system from being damaged.

The embodiment of the tractor of the present invention can have the safety device of the lifting system of the above embodiment, i.e. all technical solutions of the safety device embodiment of the above lifting system are adopted, so that all the beneficial effects brought by the technical solutions of the safety device embodiment of the above lifting system are at least provided.

The preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited thereto. The technical idea of the utility model within the scope, can be right the utility model discloses a technical scheme carries out multiple simple variant, makes up with any suitable mode including each concrete technical feature. In order to avoid unnecessary repetition, the present invention does not separately describe various possible combinations. These simple variations and combinations should also be considered as disclosed in the present invention, all falling within the scope of protection of the present invention.

Claims (10)

1. The utility model provides a safety device of lifting system, its characterized in that includes hydraulic pump (2), lift valve (3), operating valve (4) and pneumatic switch (5) of being connected with motor (1), hydraulic pump (2) pass through lift valve (3) are connected with lift cylinder (6), operating valve (4) through first gas circuit (71) and second gas circuit (72) with two spring control chambeies of lift valve (3) are connected respectively, pneumatic switch (5) are located on first gas circuit (71) and second gas circuit (72), in order to control the switching-over of lift valve (3), pneumatic switch (5) with motor (1) are established ties, in order to control the opening and shutting of motor (1).

2. A safety arrangement of a lifting system according to claim 1, characterized in that the lifting valve (3) comprises a first oil port (a1) connected to the hydraulic pump (2) through an oil inlet line (81), a second oil port (a2) connected to an oil return line (82), a third oil port (A3) connected to the rodless chamber of the lifting cylinder (6) and a fourth oil port (a4) connected to the rod chamber of the lifting cylinder (6).

3. A safety arrangement of a lifting system according to claim 2, characterized in that the third port (a3) of the lifting valve (3) is connected to the rodless chamber of the lifting cylinder (6) through a balancing valve (91), the control end of the balancing valve (91) being connected to the rod chamber of the lifting cylinder (6).

4. A safety arrangement of a lifting system according to claim 2, characterized in that the fourth port (a4) of the lifting valve (3) is connected to the oil return line (82) through a throttle valve (92).

5. A safety device of a lifting system as claimed in claim 2, characterized in that a filter (93) is arranged on the oil return path (82), and an oil return check valve (94) is connected in parallel on the filter (93) to enable hydraulic oil to be introduced into the oil tank unidirectionally; and an oil inlet one-way valve (96) is arranged on the oil inlet oil way (81) so as to enable the hydraulic oil flowing out of the hydraulic pump (2) to be led into the lifting valve (3) in a one-way mode.

6. A safety device of a lifting system according to claim 2, characterized in that an overflow valve (95) is arranged between the oil inlet path (81) and the oil return path (82).

7. A safety device of a lifting system according to claim 1, characterized in that the pilot valve (4) is a pneumatic directional valve comprising an air inlet (B1), a first working air port (B2) connected to the first air path (71), a second working air port (B3) connected to the second air path (72) and an air outlet (B4).

8. A safety arrangement of a lifting system according to any of claims 1-7, characterized in that an anti-explosion valve (97) is arranged on the oil path between the rodless chamber of the lifting cylinder (6) and the lifting valve (3).

9. A lifting system safety device according to any of claims 1-7, characterized in that an electrical switch (98) is arranged in the electrical circuit between the pneumatic switch (5) and the motor (1).

10. Tractor, characterized in that it comprises a safety device of the lifting system according to any of claims 1-9.

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