CN204572645U - Differential hydraulic control system and hoist - Google Patents

Abstract

The embodiment of the utility model discloses a differential hydraulic control system and a crane, which relate to the field of hydraulic technology, wherein the system includes: a first reversing valve (1), a second reversing valve (2), a one-way valve (3 ), torque limiter (4) and controller (5), the first reversing valve (1) is arranged on the oil path where the rodless cavity of the differential hydraulic cylinder (7) communicates with the oil source, and communicates with the oil tank; the second The reversing valve (2) communicates with the first reversing valve (1), the rodless chamber and the rod chamber of the differential hydraulic cylinder (7) respectively; the check valve (3) is arranged between the second reversing valve (2) and the The oil tank is connected to the oil circuit; the moment limiter (4) is connected with the controller (5), and the actual hoisting weight detected is transmitted to the controller (5); the controller (5) and the second reversing valve (2) The control end is connected to control the reversing of the second reversing valve (2), so as to realize the switching between the differential state and the non-differential state of the differential hydraulic cylinder (7).

Description

Differential hydraulic control system and crane

technical field

The utility model relates to the field of hydraulic technology, in particular to a differential hydraulic control system and a crane.

Background technique

The working action of the crane on the car consists of four actions: slewing, luffing, telescopic, and lifting. The luffing action of the crane is driven by the hydraulic cylinder. When the hydraulic cylinder is extended, the working range of the crane becomes smaller, and when the hydraulic cylinder is retracted, the working range of the crane increases.

In non-working conditions such as crane transportation and car collection, the boom is fully retracted and placed on the chassis support, and the hydraulic cylinder is at the minimum stroke position. Before the crane enters the working state, the operator operates the crane to perform a luffing action to move the crane to the working position. This process belongs to the auxiliary stroke (also called the non-working stroke). During the auxiliary stroke, the operator wants the hydraulic cylinder to be as fast as possible, so as to reduce the auxiliary working time.

After the crane reaches the working position, it lifts the heavy object, and then performs luffing action to make the heavy object reach the proper position. At this time, the hydraulic cylinder is required to provide a large working thrust to meet the lifting needs of the crane. At the same time, it is hoped that the luffing and micro-movement performance is good, that is, the lower the speed of the hydraulic cylinder, the better, so as to meet the needs of lifting operations. This process belongs to the working stroke, and the hydraulic cylinder of the crane is required to provide large thrust and low speed.

After the work of the crane is completed, it is necessary to carry out the luffing action of the crane to put the boom on the chassis support. This process is an auxiliary stroke, and the faster the speed, the better.

To sum up: the luffing motion of the crane is divided into two parts, the auxiliary stroke and the working stroke. The auxiliary stroke requires the hydraulic cylinder to be fast to reduce the auxiliary working time; the working stroke requires the hydraulic cylinder to provide large thrust and slow speed to ensure fretting requirements.

However, existing hydraulic systems are either differential hydraulic systems or non-differential hydraulic systems. In the differential hydraulic system, the hydraulic cylinder is in a differential state, which can meet the requirements of the auxiliary stroke, but cannot meet the requirements of the working stroke; in the non-differential hydraulic system, the hydraulic cylinder is in a non-differential state, which can meet the requirements of the working stroke , but cannot meet the requirements of auxiliary travel. Therefore, there is an urgent need for a hydraulic system that can not only meet the requirements of the auxiliary stroke, but also meet the requirements of the working stroke.

Utility model content

An object of the embodiment of the present invention is to provide a differential hydraulic control system and a crane, which can meet the requirements of both the auxiliary stroke and the working stroke.

According to an aspect of the present invention, a differential hydraulic control system is provided, including: a first reversing valve, a second reversing valve, a check valve, a torque limiter and a controller, wherein: the first reversing valve The valve is set on the oil path where the rodless chamber of the differential hydraulic cylinder communicates with the oil source, and communicates with the oil tank; the second reversing valve communicates with the first reversing valve, the rodless chamber of the differential hydraulic cylinder and the Rod cavity; the check valve is set on the oil passage where the second reversing valve communicates with the oil tank; the torque limiter is connected with the controller, and transmits the detected actual hoisting weight to the controller The controller; the controller is connected to the control end of the second directional valve, and controls the reversing of the second directional valve to realize the switching between the differential state and the non-differential state of the differential hydraulic cylinder.

In one embodiment, the second reversing valve is a hydraulic control reversing valve; the system further includes: an electromagnetic reversing valve, and the electromagnetic reversing valve is arranged at the liquid control end of the second reversing valve The oil path between the oil source and the oil source, and the control end of the electromagnetic reversing valve is connected with the controller.

In one embodiment, a balance valve is provided on the oil passage where the first reversing valve communicates with the rodless cavity of the differential hydraulic cylinder.

In one embodiment, a relief valve is further included, the oil inlet of the relief valve communicates with the oil source, and the oil outlet of the relief valve communicates with the oil tank.

In one embodiment, the second reversing valve includes a first working position and a second working position; when the second reversing valve is in the first working position, the rod chamber of the differential hydraulic cylinder and the The oil passage between the rod cavities is connected; when the second reversing valve is in the second working position, the rod chamber of the differential hydraulic cylinder communicates with the oil passage between the first reversing valve.

In one embodiment, the first reversing valve includes a neutral position, a first working position and a second working position; the second reversing valve includes a first working position and a second working position; the first reversing valve When the directional valve is at the first working position and the second directional valve is at the first working position, the rodless cavity of the differential hydraulic cylinder is in communication with the oil source, and the rod cavity of the differential hydraulic cylinder is connected with the oil source. The oil passage between the rodless chambers is connected; when the first reversing valve is at the first working position and the second reversing valve is at the second working position, the connection between the rodless chamber of the differential hydraulic cylinder and the oil source The oil circuit is connected, and the oil circuit between the rod chamber of the differential hydraulic cylinder and the first reversing valve is connected; the first reversing valve is in the second working position, the second reversing valve When the valve is in the first working position, the rodless chamber of the differential hydraulic cylinder communicates with the oil passage between the oil tank, and the rod chamber of the differential hydraulic cylinder communicates with the oil passage between the rodless chamber; the When the first reversing valve is in the second working position and the second reversing valve is in the second working position, the rodless chamber of the differential hydraulic cylinder communicates with the oil passage between the oil tank, and the differential hydraulic pressure The rod chamber of the cylinder communicates with the oil passage between the first reversing valve.

In one embodiment, the first reversing valve is a three-position four-way valve.

In one embodiment, the second reversing valve is a two-position three-way valve.

According to another aspect of the present utility model, a crane is provided, including the differential hydraulic control system provided in any one of the above embodiments.

Embodiments of the utility model have at least the following beneficial effects:

On the one hand, according to the actual lifting weight detected by the force limiter, the current working condition requirements can be determined, so that the differential hydraulic cylinder can be switched between the differential state and the non-differential state according to actual needs, which can meet the auxiliary stroke requirements, but also to meet the requirements of the work schedule. The auxiliary stroke can provide low-pressure and high-speed working conditions to improve working efficiency; the working stroke can provide high-pressure and low-speed working conditions to meet the requirements of large thrust and micro-movement during operation.

On the other hand, there is no need to switch the state according to the operator's operating experience, which can effectively avoid misoperation, and is safe, efficient and highly intelligent.

On the other hand, the hydraulic control system is based on common hydraulic components and control elements of the crane, and has a simple structure and is easy to implement.

The technical solutions of the present utility model will be further described in detail through the drawings and embodiments below.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are only some embodiments of the utility model, and those skilled in the art can also obtain other drawings according to these drawings without any creative effort.

Fig. 1 is a schematic structural view of an embodiment of the differential hydraulic control system of the present invention;

Fig. 2 is a structural schematic diagram of another embodiment of the differential hydraulic control system of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. example. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

The relative arrangements of components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

At the same time, it should be understood that, for the convenience of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship.

Techniques, methods and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods and devices should be considered part of the Authorized Specification.

In all examples shown and discussed herein, any specific values should be construed as illustrative only, and not as limiting. Therefore, other examples of the exemplary embodiment may have different values.

It should be noted that like numerals and letters denote like items in the following figures, therefore, once an item is defined in one figure, it does not require further discussion in subsequent figures.

Firstly, the technical terms involved in the utility model are explained.

Differential hydraulic cylinder: supply pressure oil to the rodless cavity of the single-piston rod hydraulic cylinder, and then connect the oil discharged from the rod cavity back to the rodless cavity, which is called a differential hydraulic cylinder, which utilizes the difference in effective area at both ends of the hydraulic cylinder. for transmission.

Luffing: The horizontal distance from the centerline of the truck crane hook to the centerline of the crane's slewing, that is, the turning radius or working radius of the hoisted weight, is called the working range, and changing the size of the working range is called the luffing.

Gravity drop: When the working range of the crane changes from small to large (that is, when the amplitude is dropped), the power of the amplitude is generated by the self-weight of the boom, which is called gravity drop.

Moment limiter (referred to as force limiter): an independent safety operating system completely controlled by a computer, which can automatically detect the weight of the crane and the angle of the boom, and can display its rated load and actual load. Load, working radius, angle at which the jib is positioned. Real-time monitoring of crane working conditions, built-in diagnostic function, and capable of rapid alarm and sound control of dangerous conditions. In addition, it also has a black box function, which automatically records the dangerous working conditions during operation and provides a basis for accident analysis and handling.

The force limiter and controller are important parts of the crane. In the non-lifting state, the force limiter displays the weight of the hook, and in the lifting state, the force limiter displays the weight of the hook plus the hoisting weight. The controller is the control center of the crane, which can control various actions of the crane.

The crane operator hopes that in the non-lifting state (that is, auxiliary stroke), the speed of the hydraulic cylinder is large and the thrust is small, which belongs to the low-pressure high-speed working condition; , which meets the requirements of fretting, and belongs to the high-pressure and low-speed working condition.

Fig. 1 is a structural schematic diagram of an embodiment of the differential hydraulic control system of the present invention. As shown in Figure 1, the system includes: a first reversing valve 1, a second reversing valve 2, a one-way valve 3, a torque limiter 4 and a controller 5, wherein:

The first reversing valve 1 is arranged on the oil path where the rodless chamber of the differential hydraulic cylinder 7 communicates with the oil source, and communicates with the oil tank; the second reversing valve 2 communicates with the first reversing valve 1 and the differential hydraulic cylinder 7 respectively. There are rodless chamber and rod chamber; the check valve 3 is set on the oil circuit where the second reversing valve 2 communicates with the oil tank; the moment limiter 4 is connected with the controller 5 and transmits the detected actual hoisting weight to the controller 5; The controller 5 is connected to the control end of the second reversing valve 2 to control the reversing of the second reversing valve 2 to realize the switching between the differential state and the non-differential state of the differential hydraulic cylinder 7 .

The actual hoisting weight G detected by the moment limiter can reflect whether the crane is in the hoisting state or in the non-hoisting state. Specifically, a threshold G' can be set, for example, the threshold G' can be set to be the weight of the hook or greater than the weight of the hook.

The controller can read the actual hoisting weight G detected by the moment limiter, and compare the actual hoisting weight G with the threshold G'. When the actual hoisting weight G is less than the threshold G', it can be determined that the crane is in a non-hoisting state, that is The auxiliary stroke controls the reversing of the second reversing valve to control the differential hydraulic cylinder in a differential state, so as to meet the requirements of low-pressure and high-speed working conditions with high speed and small thrust. Of course, if the current differential hydraulic cylinder is already in the differential state, the controller does not need to control the second reversing valve to reversing.

When the actual hoisting weight G is greater than the threshold G', it can be determined that the crane is in the hoisting state, that is, the working stroke, so the second reversing valve is controlled to control the differential hydraulic cylinder in a non-differential state, so as to meet the minimum speed High-thrust high-pressure low-speed working conditions. Of course, if the current differential hydraulic cylinder is already in the non-differential state, the controller does not need to control the reversing of the second reversing valve.

According to the actual lifting weight detected by the force limiter, the embodiment of the utility model can determine the current working condition requirements, so that the differential hydraulic cylinder can be switched between the differential state and the non-differential state according to actual needs, which can meet the The requirements of the auxiliary stroke can also meet the requirements of the working stroke. The auxiliary stroke can provide low-pressure and high-speed working conditions to improve working efficiency; the working stroke can provide high-pressure and low-speed working conditions to meet the requirements of large thrust and micro-movement during operation. In addition, there is no need to switch states based on the operator's operating experience, which can effectively avoid misoperation, and is safe, efficient, and highly intelligent. In addition, the hydraulic control system is based on common hydraulic components and control elements of the crane, which is simple in structure and easy to implement.

The differential hydraulic control system provided by the embodiment of the utility model is suitable for but not limited to the luffing system of the gravity drop of the crane. Since it can be switched to the differential state according to the actual situation, it can solve the problem of the small amplitude luffing of the existing gravity drop luffing system. The problem of slow falling speed. In actual application, taking the luffing action of a crane as an example, the auxiliary stroke of the crane corresponds to the luffing action of the crane without load (without lifting weight); the working stroke corresponds to the luffing action of the crane when it is hoisting. Because there will be lifting, turning, telescopic and other actions between the auxiliary stroke and the working stroke of the crane, that is, there will be a certain operation interval between the no-load luffing and the loaded luffing of the crane, so the controller can be read as a force limiter. The time interval of the actual lifting weight G is set to be smaller than the operation interval, so that the hydraulic shock caused by switching between the differential state and the non-differential state of the differential hydraulic cylinder can be avoided.

It should be noted that the functions of the controller in the present invention can be realized by software or by hardware. As an example of hardware implementation, for example, a comparator may be used to implement the function of the controller. Specifically, the comparator can compare the actual hoisting weight G with the threshold G', and when the actual hoisting weight is less than the threshold, send a low-level signal to the second reversing valve to control the differential hydraulic cylinder to be in a differential state; When the actual lifting weight is greater than the threshold, a high-level signal is sent to the second reversing valve to control the differential hydraulic cylinder to be in a non-differential state.

It should be understood that if the initial state of the differential hydraulic cylinder is a differential state, the second reversing valve does not need to reversing when receiving a low-level signal; if the initial state of the differential hydraulic cylinder is a non-differential state, the second reversing valve When the reversing valve receives a low-level signal, it needs to reversing to realize the switching of the differential hydraulic cylinder from the non-differential state to the differential state.

In addition, the control method for the second reversing valve can also be reversed, that is, when the actual hoisting weight is less than the threshold value, a high-level signal is sent to the second reversing valve; Send a low level signal to the valve. For specific implementation, please refer to the above description.

It should be pointed out that, as a non-limiting example, the above-mentioned oil source may be realized by, for example, a hydraulic pump and an oil tank, or may be any other form of oil source.

In the differential hydraulic control system of the present utility model, the second reversing valve 2 can be either an electromagnetic reversing valve or a hydraulic control reversing valve, and the two cases will be described respectively below.

In one case, referring to Fig. 1, the second reversing valve 2 can be an electromagnetic reversing valve, and the controller can control its reversing by sending an electric signal to the electromagnetic reversing valve, so as to realize the differential state of the differential hydraulic cylinder 7 and Switching of non-differential state. For the specific switching process, refer to the description of the above embodiment.

In another case, referring to another embodiment of the differential hydraulic control system of the present invention shown in FIG. 2 , the second reversing valve 2 may be a hydraulically controlled reversing valve. Correspondingly, the system further includes: an electromagnetic reversing valve 10, which is arranged on the oil circuit between the liquid control end of the second reversing valve 2 and the hydraulic oil source, and the control of the electromagnetic reversing valve 10 Terminal is connected with controller 5. Here, the hydraulic oil source can be the oil source shown in Figure 2, or can be taken from other stable oil sources.

In this case, taking the switching from a differential state to a non-differential state as an example, when it is necessary to control the reversing of the second reversing valve 2, for example, the controller can send an electric signal to the electromagnetic reversing valve 10, so that the electromagnetic reversing valve The directional valve 10 works in the left position, and then the control oil passes through the electromagnetic directional valve 10 to act on the liquid control end of the hydraulic control directional valve 2, so that the hydraulic control directional valve 2 is in the right position, ending the differential operation of the hydraulic cylinder in the system state, so that the hydraulic cylinder is in a non-differential state. At this time, the hydraulic cylinder provides high-pressure and low-speed working conditions to meet the requirements of large thrust and micro-motion of the crane. Similarly, those skilled in the art can determine how the controller controls the electromagnetic reversing valve 10 and the second reversing valve 2 when switching from the non-differential state to the differential state, so details will not be repeated here.

As a specific example, the second reversing valve 2 may include a first working position and a second working position. When the second reversing valve 2 is in the first working position, the rod chamber of the differential hydraulic cylinder 7 and the rodless The oil circuit between the cavities is connected. At this time, the differential hydraulic cylinder is in the differential state; when the second reversing valve 2 is in the second working position, the rod chamber of the differential hydraulic cylinder 7 and the first reversing valve 1 The oil circuit between them is connected, at this time, the differential hydraulic cylinder is in a non-differential state.

As another specific embodiment, the first reversing valve 1 may include a neutral position, a first working position and a second working position, and the second reversing valve 2 may include a first working position and a second working position. For example, the first reversing valve 1 may be a three-position, four-way valve, and the second reversing valve 2 may be a two-position, three-way valve. However, the present invention is not limited thereto, and the functions of the first reversing valve and the second reversing valve can also be realized by other valves.

When the differential hydraulic cylinder is extended or retracted, it can switch between the differential state and the non-differential state. By controlling the working position of the first reversing valve, the extension or retraction state of the differential hydraulic cylinder can be controlled.

The differential extension/retraction state and the non-differential extension/retraction state of the differential hydraulic cylinder will be described below in conjunction with the working positions of the first reversing valve and the second reversing valve.

When the first reversing valve 1 is at the first working position and the second reversing valve 2 is at the first working position, the rodless cavity of the differential hydraulic cylinder 7 is connected with the oil path between the oil source, and the differential hydraulic cylinder The oil path between the rod chamber of 7 and the rodless chamber is communicated. At this time, the differential hydraulic cylinder 7 is in a differential extension state. The hydraulic oil from the oil source enters the rodless chamber of the differential hydraulic cylinder 7 through the first reversing valve 1, and a part of the hydraulic oil in the rod chamber of the differential hydraulic cylinder 7 can flow to The rodless cavity of the differential hydraulic cylinder 7 increases the extension speed of the differential hydraulic cylinder 7 .

When the first reversing valve 1 is at the first working position and the second reversing valve 2 is at the second working position, the rodless chamber of the differential hydraulic cylinder 7 communicates with the oil path between the oil source, and the differential hydraulic cylinder The rod chamber of 7 communicates with the oil path between the first reversing valve 1. At this time, the differential hydraulic cylinder 7 is in a non-differential extension state. The hydraulic oil from the oil source enters the rodless chamber of the differential hydraulic cylinder 7 through the first reversing valve 1, and the hydraulic oil in the rod chamber of the differential hydraulic cylinder 7 flows to the first reversing valve after passing through the second reversing valve 2 1, and then flow into the fuel tank.

When the first reversing valve 1 is at the second working position and the second reversing valve 2 is at the first working position, the rodless chamber of the differential hydraulic cylinder 7 communicates with the oil passage between the oil tank, and the differential hydraulic cylinder 7 The rod chamber and the rodless chamber communicate with the oil passage between them. At this time, the differential hydraulic cylinder 7 is in a differentially retracted state. Part of the hydraulic oil in the rodless chamber of the differential hydraulic cylinder 7 flows into the oil tank through the first reversing valve 1, and the other part flows into the rod chamber of the differential hydraulic cylinder 7 through the second reversing valve 2, increasing the differential hydraulic pressure. Retraction speed of cylinder 7.

When the first reversing valve 1 is in the second working position and the second reversing valve 2 is in the second working position, the rodless chamber of the differential hydraulic cylinder 7 is connected to the oil passage between the oil tank, and the differential hydraulic cylinder 7 The oil passage between the rod cavity and the first reversing valve 1 is communicated. The hydraulic oil in the rodless chamber of the differential hydraulic cylinder 7 flows into the fuel tank through the first reversing valve 1, and the hydraulic oil in the fuel tank is supplied to the rod chamber of the differential hydraulic cylinder 7 through the check valve 3 and the second reversing valve 2. Oil.

In addition, as a specific example of the first reversing valve 1, when the first reversing valve 1 is in the neutral position, the second reversing valve 2 can pass through the orifice in the stem of the first reversing valve 1 and the fuel tank. connected. At this time, the differential hydraulic cylinder 7 neither extends nor retracts.

In yet another embodiment of the differential hydraulic control system of the present utility model, referring to Fig. 1 or Fig. 2, a balance valve 8 is provided on the oil circuit where the first reversing valve 1 communicates with the rodless cavity of the differential hydraulic cylinder 7, so as to Ensure that the speed of the differential hydraulic cylinder 7 is stable when retracting, and avoid the occurrence of a stall phenomenon.

In yet another embodiment of the differential hydraulic control system of the present invention, referring to Fig. 1 or Fig. 2, it may also include a relief valve 9, the oil inlet of the relief valve 9 is connected to the oil source, and the oil outlet of the relief valve 9 The port connects to the fuel tank. The supply pressure of the system can be limited by setting the relief valve, for example, when the system pressure is greater than 20MPa, the relief valve is opened to reduce the supply pressure of the system.

The differential hydraulic control system of the utility model can be applied to a crane.

In one embodiment of the crane provided by the utility model, the hydraulic differential control system in any of the above embodiments may be included.

Those of ordinary skill in the art can understand that all or part of the steps for realizing the above-mentioned method embodiments can be completed by hardware related to program instructions, and the aforementioned program can be stored in a computer-readable storage medium. When the program is executed, the It includes the steps of the above method embodiments; and the aforementioned storage medium includes: ROM, RAM, magnetic disk or optical disk and other various media that can store program codes.

In the description of the present utility model, it should be understood that the use of words such as "first" and "second" to define parts is only for the convenience of distinguishing the above parts. If there is no other statement, the above words do not There is no special meaning, so it cannot be interpreted as limiting the protection scope of the present utility model.

The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and changes will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to better explain the principle and practical application of the invention, and to enable those of ordinary skill in the art to understand the invention and design various embodiments with various modifications suitable for particular purposes.

Claims (9)

1. A differential hydraulic control system, characterized in that it comprises: a first reversing valve (1), a second reversing valve (2), a one-way valve (3), a torque limiter (4) and a controller (5), where: The first reversing valve (1) is arranged on the oil path where the rodless chamber of the differential hydraulic cylinder (7) communicates with the oil source, and communicates with the oil tank; the second reversing valve (2) communicates with the first reversing valve respectively. A reversing valve (1), a rodless chamber and a rod chamber of a differential hydraulic cylinder (7); On the oil circuit; the moment limiter (4) is connected with the controller (5), and transmits the detected actual hoisting weight to the controller (5); the controller (5) communicates with the second commutation The control end of the valve (2) is connected to control the reversing of the second reversing valve (2), so as to realize the switching between the differential state and the non-differential state of the differential hydraulic cylinder (7). 2. The system according to claim 1, characterized in that, the second reversing valve (2) is a hydraulic control reversing valve; The system also includes: an electromagnetic reversing valve (10), the electromagnetic reversing valve (10) is arranged on the oil circuit between the liquid control end of the second reversing valve (2) and the oil source, and the The control end of the electromagnetic reversing valve (10) is connected with the controller (5). 3. The system according to claim 1, characterized in that, a balance valve (8) is provided on the oil passage where the first reversing valve (1) communicates with the rodless cavity of the differential hydraulic cylinder (7). 4. The system according to claim 1, further comprising a relief valve (9), the oil inlet of the relief valve (9) is connected to the oil source, and the outlet of the relief valve (9) The oil port communicates with the oil tank. 5. The system according to claim 1, characterized in that, the second reversing valve (2) comprises a first working position and a second working position; When the second reversing valve (2) is in the first working position, the oil path between the rod chamber and the rodless chamber of the differential hydraulic cylinder (7) is connected; the second reversing valve (2 ) in the second working position, the rod chamber of the differential hydraulic cylinder (7) communicates with the oil passage between the first reversing valve (1). 6. The system according to claim 1, characterized in that, the first reversing valve (1) includes a neutral position, a first working position and a second working position; the second reversing valve (2) includes The first working position and the second working position; When the first reversing valve (1) is at the first working position and the second reversing valve (2) is at the first working position, the distance between the rodless cavity of the differential hydraulic cylinder (7) and the oil source The oil circuit is connected, and the oil circuit between the rod chamber and the rodless chamber of the differential hydraulic cylinder (7) is connected; the first reversing valve (1) is in the first working position, and the second reversing valve (2) At the second working position, the oil path between the rodless chamber of the differential hydraulic cylinder (7) and the oil source communicates, and the rod chamber of the differential hydraulic cylinder (7) and the first The oil circuit between the reversing valves (1) is connected; When the first reversing valve (1) is at the second working position and the second reversing valve (2) is at the first working position, the gap between the rodless cavity of the differential hydraulic cylinder (7) and the oil tank The oil circuit of the differential hydraulic cylinder (7) is connected with the oil circuit between the rod chamber and the rodless chamber; the first reversing valve (1) is in the second working position, the second reversing valve When the direction valve (2) is at the second working position, the rodless chamber of the differential hydraulic cylinder (7) communicates with the oil passage between the oil tank, and the rod chamber of the differential hydraulic cylinder (7) and the The oil passage between the first reversing valve (1) is connected. 7. The system according to claim 1, characterized in that, the first reversing valve (1) is a three-position four-way valve. 8. The system according to claim 1, characterized in that the second reversing valve (2) is a two-position three-way valve. 9. A crane, characterized in that it comprises the differential hydraulic control system according to any one of claims 1-8.