CN213472901U

CN213472901U - Safety device of lifting system and dump truck

Info

Publication number: CN213472901U
Application number: CN202022037007.4U
Authority: CN
Inventors: 吴威; 刘玉杰; 任泽星; 王若婷; 秦宬
Original assignee: BYD Co Ltd; Shanwei BYD Automobile Co Ltd
Current assignee: BYD Co Ltd; Shanwei BYD Automobile Co Ltd
Priority date: 2020-09-15
Filing date: 2020-09-15
Publication date: 2021-06-18
Anticipated expiration: 2030-09-15

Abstract

The utility model relates to a lifting device discloses a safety device of system of lifting, include the hydraulic pump of being connected with the motor, lift valve, operating valve and baroswitch, the hydraulic pump passes through lift valve and hydraulic cylinder connection, the operating valve through first gas circuit and second gas circuit with two control ends of the valve of lifting are connected respectively, in order to control the switching-over of the valve of lifting, arrange on the first gas circuit baroswitch with be used for the restriction the spacing valve of hydraulic cylinder lifting height, in order to pass through baroswitch and spacing valve control the break-make of first gas circuit, the baroswitch with the motor is established ties, in order to control opening and close of motor. The utility model also discloses a tipper. The utility model discloses a safety device of system of lifting can the self-closing motor to make the hydraulic pump stop work, prevent the system damage.

Description

Safety device of lifting system and dump truck

Technical Field

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

Background

The dumper is a vehicle which can unload goods automatically by hydraulic or mechanical lifting, and is also called as a dumper, and consists of an automobile chassis, a hydraulic lifting mechanism, a goods compartment, a power takeoff device and the like. In civil engineering, a dump truck is often operated in conjunction with an engineering machine such as an excavator, a loader, a belt conveyor, etc. to form a loading, transporting, and unloading line for loading, unloading, and transporting earthwork, gravel, and bulk materials.

The Chinese patent application with the application number of CN201810750318.X discloses an energy-saving device of a lifting system of a mining dump truck, which comprises a hydraulic oil tank, a ball valve, an oil return filter, an air filter, a power takeoff, a gear pump, a lifting valve group, a hydraulic cylinder, a limiting valve and an air control valve. The connection between the power takeoff and the gear pump is realized by controlling the power takeoff through the pneumatic control valve. When the mining dump truck is in a lifting state, the power takeoff is meshed with the gear pump, and the container can realize three working states of lifting, descending and keeping; the pneumatic control valve is adopted to control the power takeoff, and two working states of running or stopping of the gear pump are realized. However, if an operation error occurs, after the lifting system finishes working, the power takeoff is still in an engaged position, the hydraulic pump can operate at a high speed for a long time without load, so that the temperature of hydraulic oil rises quickly, the oil seal of the hydraulic pump is easily damaged, and even the hydraulic pump burns out, so that the system is damaged.

To this end, it is necessary to design a new safety device for a lifting system to 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 self-closing motor to make the hydraulic pump stop work, prevent that the system from damaging.

The utility model discloses the technical problem that further will solve provides a tipper, and this tipper 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 air pressure switch, the hydraulic pump passes through lift valve and hydraulic cylinder connection, the control valve through first gas circuit and second gas circuit with two control ends of lift valve are connected respectively, in order to can control the switching-over of lift valve, arrange on the first gas circuit air pressure switch with be used for the restriction hydraulic cylinder lifts high limit valve, in order to pass through air pressure switch and limit valve control the break-make of first gas circuit, air pressure switch with the motor is established ties, in order to control opening and close of motor.

Preferably, the lifting valve comprises a lifting reversing valve, the lifting reversing valve comprises a first oil port connected with the hydraulic pump, a second oil port connected with the oil tank and a third oil port connected with the hydraulic oil cylinder through a lifting oil path, the third oil port of the lifting reversing valve can be selectively communicated with the first oil port or the second oil port, and the first air path and the second air path are correspondingly connected with the two spring control cavities of the lifting reversing valve one by one.

More preferably, the lifting oil path is connected with the second oil port of the lifting reversing valve through an overflow valve.

Furthermore, a throttle valve is further arranged on an oil path between the overflow valve and a second oil port of the lifting reversing valve, and the lifting oil path is connected with a spring control cavity corresponding to the second air path on the lifting reversing valve through the overflow valve.

Preferably, the first oil port of the lifting reversing valve is connected with the hydraulic pump through an oil inlet check valve so as to enable hydraulic oil to be introduced into the lifting reversing valve in a single direction; the second hydraulic fluid port of lifting reversing valve pass through the filter with the oil tank is connected, just it has the oil return check valve to connect in parallel on the filter to can make hydraulic oil single-direction introduction the oil tank.

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.

Optionally, the pilot valve is a handle-style pneumatic directional valve.

Optionally, the limit valve is an air pressure ejector rod type limit valve, and an electric switch is arranged on a circuit between the air pressure switch and the motor.

Preferably, the pneumatic switch is located between the lifting valve and the limit valve.

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

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

the utility model discloses an among the basic technical scheme, set up air pressure switch ingeniously on first gas circuit, after lift cylinder lifts to target in place, touch the limit valve, cut off first gas circuit, air pressure switch on first gas circuit is in the off-state because can not feel atmospheric pressure to the circuit cut-off, self-closing motor makes the hydraulic pump stall, prevents that the part on the hydraulic pump even hydraulic pump from damaging, protection system safety.

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 electric motor 11 electrical equipment switch

2 hydraulic pump 3 lifting valve

A1 Lift shuttle valve first port A2 Lift shuttle valve second port

Overflow valve of third port 31 of A3 lifting reversing valve

32 throttling valve 33 oil inlet one-way valve

Air inlet of 4-way valve B1 pneumatic reversing valve

First working gas port of B2 pneumatic reversing valve B3 second working gas port of pneumatic reversing valve

Air outlet 5 air pressure switch of B4 pneumatic reversing valve

6 hydraulic cylinder 71 first air path

72 second air path 73 lifting oil path

8 limiting valve 91 filter

92 oil return check valve

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" 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 "first", "second", "third" 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 hydraulic cylinder 6 through lifting valve 3, operating valve 4 is connected respectively through first gas circuit 71 and second gas circuit 72 and two control ends of lifting valve 3, with the switching-over that can control lift valve 3, baroswitch 5 and the stop valve 8 that is used for restricting hydraulic cylinder 6 lifting height have been arranged on first gas circuit 71, with the break-make that can control first gas circuit 71 through baroswitch 5 and stop valve 8, baroswitch 5 establishes ties with motor 1, with the start and stop that can control motor 1.

The energy-saving device of the existing mining dump truck lifting system adopts a pneumatic control valve to control a power takeoff, if misoperation occurs, for example, a dump truck drives without being separated from the power takeoff after unloading, so that the power takeoff is in an engaged state after the lifting system finishes working, or a handle is in failure and loses control over the power takeoff; this will make the hydraulic pump in the high-speed no-load operation for a long time, lead to the hydraulic oil temperature to rise very fast, make the system keep warming up and damage the system easily.

However, the safety device of the lifting system of the present invention originally sets the air pressure switch 5 in the control loop, and controls the on and off of the circuit where the motor 1 is located through the air pressure switch 5, so as to control the operation of the hydraulic pump 2; specifically, the air pressure switch 5 can be closed by sensing air pressure through the operating valve 4, the first air path 71 is conducted, the lifting valve 3 is further reversed, the circuit where the motor 1 is located is conducted, the motor 1 drives the hydraulic pump 2 to operate, and the hydraulic oil cylinder 6 is driven to lift; when the hydraulic oil cylinder 6 is lifted to the right position, the limit valve 8 is touched, the limit valve 8 cuts off the first air channel 71, the air pressure switch 5 is disconnected, the circuit where the motor 1 is located is cut off, the operation of the hydraulic pump 2 is stopped, and the situation that the hydraulic pump 2 is in long-time high-speed no-load operation due to errors, so that the system is continuously heated and damaged is prevented; moreover, the operating valve 4 can also control the lifting valve 3 to change the direction through the second air passage 72, and can perform descending operation on the hydraulic oil cylinder 6, so that the hydraulic oil cylinder 6 automatically descends under the action of gravity; therefore, the gas circuit matching relationship is simple, and the structure is simple.

In a specific embodiment, the lifting valve 3 includes a lifting reversing valve, which is preferably a pneumatic three-position three-way valve, and the lifting reversing valve has three oil ports, i.e., a first oil port a1, a second oil port a2, a third oil port A3, and the like, the first oil port a1 of the lifting reversing valve is connected with the hydraulic pump 2, the second oil port a2 thereof is connected with the oil tank, and the third oil port A3 thereof is connected with the hydraulic cylinder 6 through a lifting oil path 73; controlling the operating valve 4, injecting gas into a first gas path 71 from a gas source through the operating valve 4 to enable a gas pressure switch 5 to feel gas pressure and close, starting the motor 1, simultaneously injecting gas into a spring control chamber of the lifting reversing valve through the first gas path 71, communicating the other spring control chamber of the lifting reversing valve with the operating valve 4 and the atmosphere through a second gas path 72 to control the reversing of the lifting reversing valve, enabling the lifting reversing valve to be in a right position function, communicating a first oil port A1 of the lifting reversing valve with a third oil port A3 thereof to enable the hydraulic pump 2 to convey hydraulic oil to the hydraulic oil cylinder 6, driving the hydraulic oil cylinder 6 to lift, after the hydraulic oil cylinder 6 touches the limiting valve 8, cutting off the first gas path 71 by the limiting valve 8, enabling the gas in the spring control chamber of the lifting reversing valve corresponding to the first gas path 71 to flow out through the limiting valve 8, enabling the lifting reversing valve to return to a middle position, and enabling the gas pressure switch 5 to be unable to close, cutting off the circuit, closing the motor 1 and stopping the operation of the hydraulic pump 2; then, the operating valve 4 can be switched to communicate the second air passage 72 with the air source through the operating valve 4, so that air is injected into the spring control cavity of the lifting reversing valve corresponding to the second air passage 72, and the hydraulic oil cylinder 6 descends under the action of gravity, wherein the hydraulic oil cylinder 6 is preferably a telescopic cylinder, and the hydraulic pump 2 is preferably a gear pump.

The technical scheme that the lifting reversing valve adopts the pneumatic control three-position three-way valve is described above, and it should be noted that the lifting reversing valve can also adopt other pneumatic control valves capable of realizing the same function, for example, the lifting reversing valve can be a pneumatic control three-position four-way valve, and correspondingly, the hydraulic oil cylinder 6 adopts a single-piston rod cylinder; the pneumatic control three-position four-way valve is respectively connected with a rod cavity and a rodless cavity of the single-piston rod cylinder so as to control the lifting of the hydraulic oil cylinder 6. Further, the limit valve 8 is preferably a pneumatic ram-type limit valve.

The oil inlet check valve 33 is further installed at the first oil port a1 of the lift directional control valve, so that the hydraulic oil flows from the hydraulic pump 2 to the lift directional control valve in a single direction, and the hydraulic oil is prevented from flowing back. The second port a2 of the lift switch valve is connected to the oil tank through a filter 91, and the filter 91 is connected in parallel with a return check valve 92, so that the hydraulic oil passing through the second port a2 of the lift switch valve flows back to the oil tank through the filter 91, and when the filter 91 is clogged or the flow rate is too large, the hydraulic oil can flow back to the oil tank through the parallel return check valve 92. An electric switch 11 can be arranged on a circuit between the air pressure switch 5 and the motor 1, and the electric switch 11 is used as a lead-in switch of a power supply and has various types, such as a combination switch, a rocker switch and the like.

As a preferred embodiment, the lifting oil path 73 is branched to form a branch oil path, the branch oil path is connected to the second port a2 of the lifting reversing valve, and the overflow valve 31 is installed on the branch oil path, so that the pressure in the lifting oil path 73 is prevented from being too high during the descending process of the hydraulic oil cylinder 6, and the stability of the system pressure is ensured. Furthermore, the branch oil path is also provided with a throttle valve 32, when hydraulic oil flows through the throttle valve 32, a back pressure is formed in a reservoir of the throttle valve 32, and the hydraulic oil cylinder 6 is ensured to descend stably; moreover, the spring control chamber of the lift switch valve corresponding to the second air passage 72 is connected to the oil passage between the relief valve 31 and the throttle valve 32, and when the pressure in the lift oil passage 73 is too high, a part of the hydraulic oil flowing through the branch oil passage flows into the spring control chamber of the lift switch valve corresponding to the second air passage 72, so that the opening degree of the valve port of the lift switch valve is increased, and the hydraulic oil can flow to the oil tank quickly.

In 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 path 71, and the second working air port B3 of the pneumatic directional control valve is connected to the second air path 72. When the control valve 4 is in a left position function, an air source is communicated with the first air path 71 through an air inlet B1 and a first working air port B2 of the pneumatic reversing valve, so that the air pressure switch 5 is closed, air is injected into a spring control cavity of the lifting reversing valve, the hydraulic pump 2 supplies oil to the hydraulic oil cylinder 6, and the hydraulic oil cylinder 6 is driven to do lifting action; when the operating valve 4 is in the neutral position function, the first air path 71 and the second air path 72 are both communicated with the atmosphere, so that the lifting reversing valve is also in the neutral position function, and the first oil port A1 of the lifting reversing valve is communicated with the second oil port A2 thereof, namely the hydraulic pump 2 is communicated with the oil return path; when the operating valve 4 is in the right 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 lifting reversing valve is in the left position function, and the hydraulic oil cylinder 6 can descend under the action of gravity.

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.

The pneumatic switch 5 may be located between the pilot valve 4 and the limit valve 8 as shown in fig. 1, or between the lift valve 3 and the limit valve 8, and may automatically close the motor 1.

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, a pneumatic switch 5 and a limit valve 8, wherein the hydraulic pump 2 is connected to a motor 1, the motor 1 drives the hydraulic pump 2 to operate, and a stop 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 lifting valve 3 comprises an air-controlled three-position three-way valve, a first oil port A1 of the air-controlled three-position three-way valve is provided with an oil inlet one-way valve 33, hydraulic oil output by the hydraulic pump 2 can flow to the first oil port A1 of the air-controlled three-position three-way valve in a single direction, a second oil port A2 of the air-controlled three-position three-way valve is connected with an oil tank through a filter 91, the filter 91 is connected in parallel with an oil return one-way valve 92, a third oil port A3 of the air-controlled three-position three-way valve is connected with a hydraulic oil cylinder 6 through a lifting oil path 73, the hydraulic oil cylinder 6 is a telescopic cylinder, the lifting oil path 73 is connected with a second oil port A2 of the air-controlled three-position three-way valve through a branch oil path, the branch oil path is sequentially provided with an overflow valve 31 and a throttle valve 32, one spring control cavity of the air-controlled three-, the operating valve 4 is a pneumatic three-position four-way valve, an air inlet B1 of the operating valve 4 is connected with an air source, an air outlet of the operating valve 4 is connected with the atmosphere, and the operating valve 4 is preferably of a handle type; pneumatic switch 5 and limit valve 8 are installed on first gas circuit 71, and pneumatic switch 5 still with motor 1 place circuit connection to can control opening and close of motor 1, moreover, still install the rocker switch on the circuit of motor 1 place.

The utility model discloses installed air pressure switch 5 ingeniously in the gas circuit, closed and the disconnection through air pressure switch 5, both can control the valve 3 of lifting, and drive hydraulic cylinder 6 is the action of lifting, also can control the start-up and the stop of motor 1 to the operation of control hydraulic pump 2 can prevent effectively that the system that the maloperation leads to from lasting intensification and damage the system.

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 lifting movement is carried out, the rocker switch is closed, the operating valve 4 is located at a left position, the air inlet B1 of the operating valve 4 is communicated with the first working air port B2, the air pressure switch 5 is closed when sensing air pressure, then, air acts on a spring control cavity at one end of the lifting reversing valve of the lifting valve 3 through the first air path 71, the lifting reversing valve is located at a right position, the first oil port A1 of the lifting reversing valve is communicated with the third oil port A3 of the lifting reversing valve, meanwhile, the motor 1 is powered to run due to the closing of the air pressure switch, the hydraulic pump 2 is driven to supply oil to the hydraulic oil cylinder 6 through the first oil port A1 and the third oil port A3 of the lifting reversing valve, and the hydraulic oil cylinder 6 is driven to carry out lifting movement; when the hydraulic oil cylinder 6 is lifted to the right position, the limit valve 8 is triggered, the limit valve 8 is switched to the right position, the first air passage 71 is cut off, the lifting reversing valve returns to the middle position, the hydraulic oil cylinder 6 stops lifting action, the air pressure switch 5 is switched off, and the motor 1 is powered off and stops, so that the hydraulic pump 2 also stops running; therefore, the system can be effectively prevented from being damaged due to continuous temperature rise of the system caused by misoperation;

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 descending, make the operating valve 4 be located the right machine ability, the air pressure switch 5 still is in the off-state because can not feel atmospheric pressure, the air inlet B1 of operating valve 4 switches on rather than second work gas port B3, make gas can act on the other end spring control chamber of the switching-over valve that lifts of valve 3 through second gas circuit 72, make the switching-over valve that lifts be in the left machine ability, make the second hydraulic fluid port A2 of the switching-over valve that lifts switch on rather than third hydraulic fluid port A3, hydraulic cylinder 6 communicates with the oil tank, descending motion is carried out under the action of gravity, motor 3 still is not switched on, hydraulic pump 2 does not run and generates heat.

According to the working process, the utility model has no complex gas circuit matching relationship, only needs to add an air pressure switch, and has simple structure; after the lifting is in place, the motor can be automatically closed, so that the damage of a hydraulic pump oil seal caused by continuous rising of the oil temperature and even the damage of a system caused by the burning-out phenomenon of a hydraulic pump are effectively avoided.

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 utility model discloses a tipper's embodiment can have above-mentioned embodiment the safety device of system of lifting, adopted above-mentioned whole technical scheme of the safety device embodiment of system of lifting promptly, consequently have all beneficial effects that the technical scheme of the safety device embodiment of above-mentioned system of lifting brought at least.

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

1. A safety device of a lifting system is characterized by comprising a hydraulic pump (2) connected with a motor (1), a lifting valve (3), an operating valve (4) and an air pressure switch (5), the hydraulic pump (2) is connected with a hydraulic oil cylinder (6) through the lifting valve (3), the operating valve (4) is respectively connected with two control ends of the lifting valve (3) through a first air path (71) and a second air path (72), so as to control the reversing of the lifting valve (3), the first air path (71) is provided with the air pressure switch (5) and a limit valve (8) for limiting the lifting height of the hydraulic oil cylinder (6), so that the on-off of the first air path (71) can be controlled by the air pressure switch (5) and the limit valve (8), the air pressure switch (5) is connected with the motor (1) in series so as to control the opening and closing of the motor (1).

2. The safety device of a lifting system according to claim 1, wherein the lifting valve (3) comprises a lifting reversing valve, the lifting reversing valve comprises a first oil port (A1) connected with the hydraulic pump (2), a second oil port (A2) connected with an oil tank and a third oil port (A3) connected with the hydraulic oil cylinder (6) through a lifting oil path (73), the third oil port (A3) of the lifting reversing valve can be selectively communicated with the first oil port (A1) or the second oil port (A2), and the first air path (71) and the second air path (72) are connected with two spring control cavities of the lifting reversing valve in a one-to-one correspondence manner.

3. A safety arrangement of a lifting system according to claim 2, characterized in that the lift circuit (73) is connected to the second port (a2) of the reversing lift valve via an overflow valve (31).

4. A safety device of a lifting system according to claim 3, characterized in that a throttle valve (32) is further arranged on an oil path between the overflow valve (31) and the second oil port (a2) of the lifting reversing valve, and the lifting oil path (73) is connected through the overflow valve (31) and a spring control cavity corresponding to the second air path (72) on the lifting reversing valve.

5. A safety arrangement of a lifting system according to claim 2, characterized in that the first port (a1) of the lift switch valve is connected to the hydraulic pump (2) through an oil inlet check valve (33) to enable hydraulic oil to be led uni-directionally to the lift switch valve; the second oil port (A2) of the lifting reversing valve is connected with the oil tank through a filter (91), and an oil return one-way valve (92) is connected to the filter (91) in parallel so that hydraulic oil can be led into the oil tank in a single direction.

6. 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).

7. A safety arrangement for a lifting system according to claim 6, characterised in that the pilot valve is a handle-type pneumatic directional control valve.

8. A lifting system safety device according to any of claims 1-7, characterised in that the limit valve (8) is a pneumatic ram-type limit valve, and that an electrical switch (11) is arranged in the electrical circuit between the pneumatic switch (5) and the motor (1).

9. A lifting system safety device according to any of claims 1-7, characterised in that the pneumatic switch (5) is located between the lifting valve (3) and a limit valve (8).

10. A dump truck characterized by comprising a safety device of the lifting system according to any one of claims 1 to 9.