Hydraulic system for an engineering machine and its climbing ladder

Abstract

The application provides an engineering machine and a hydraulic system of a climbing ladder of the engineering machine, wherein the hydraulic system comprises: a driving mechanism adapted to drive the climbing ladder to ascend or descend; a first reversing valve, a rodless cavity of the driving mechanism is communicated with a working oil port of the first reversing valve through a first pipeline, a rod cavity of the driving mechanism is communicated with the working oil port of the first reversing valve through a second pipeline, and a pressure maintaining assembly is arranged on the first pipeline; a first power mechanism and a second power mechanism, which are respectively communicated with an oil inlet of the first reversing valve through a third pipeline and a fourth pipeline; and a pressure relief mechanism, which is connected with the pressure maintaining assembly through a fifth pipeline. The driving mechanism can be supplied with oil through the first power mechanism or the second power mechanism, thereby realizing a driving mode of multi-power source combination of the climbing ladder and improving the driving efficiency of the climbing ladder. Meanwhile, the climbing ladder can descend through its own gravity without consuming the energy of the first power mechanism and the second power mechanism, thereby achieving the effect of saving energy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydraulic transmission system, in particular to an engineering machine and a hydraulic system of a ladder thereof. BACKGROUND

[0002] With the increase of China's economic strength and the rapid growth of national construction demand, the tonnage of mobile engineering machines is also getting larger and larger. For super large mobile engineering machines, the humanized boarding mode is an important embodiment of man-machine engineering.

[0003] Taking a super large excavator as an example, the current super large excavator is configured with a vertical ladder that can be raised and lowered, which is convenient for the driver to enter the cab from the vertical ladder. In the prior art, the super large excavator adopts a 24V DC motor to drive a hydraulic pump, thereby controlling the raising or lowering of the ladder. However, since the 24V DC motor itself has a small power, the hydraulic system has a slow speed and the control efficiency of the ladder movement is low. In addition, the power supply of the DC motor is taken from the battery on the excavator, and the weight of the ladder is large, so the consumption of the battery is also large. Multiple raising and lowering of the ladder may cause the battery to run out of power, resulting in the problem that the engine cannot be started. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the defects of low efficiency and large power consumption of the ladder raising and lowering drive mechanism of the super large excavator in the prior art, so as to provide an engineering machine and a hydraulic system of a ladder thereof.

[0005] In order to solve the above problems, the present application provides a hydraulic system of a ladder, comprising: a drive mechanism adapted to drive the ladder to rise or fall; a first directional control valve, a rodless cavity of the drive mechanism is communicated with a working oil port of the first directional control valve through a first pipeline, a rod cavity of the drive mechanism is communicated with the working oil port of the first directional control valve through a second pipeline, and a pressure maintaining assembly is arranged on the first pipeline; a first power mechanism and a second power mechanism, which are respectively communicated with an oil inlet of the first directional control valve through a third pipeline and a fourth pipeline; a pressure relief mechanism connected with the pressure maintaining assembly through a fifth pipeline, and the pressure relief mechanism is adapted to make the pressure maintaining assembly in an open state.

[0006] Optionally, the power source of the first power mechanism is an engine, and the power source of the second power mechanism is a motor.

[0007] Optionally, the pressure maintaining assembly comprises a sequence valve arranged on the first pipeline, the pressure relief mechanism comprises a third power mechanism and a second directional control valve, and the fifth pipeline is connected with the sequence valve.

[0008] Optionally, the hydraulic system further comprises a shuttle valve, the fifth pipeline is communicated with a first inlet of the shuttle valve, a second inlet of the shuttle valve is communicated with the second pipeline through a sixth pipeline, and an outlet of the shuttle valve is communicated with the sequence valve through a seventh pipeline.

[0009] Optionally, the second reversing valve is a manual reversing valve.

[0010] Optionally, the power source of the third power mechanism is an accumulator.

[0011] Optionally, the hydraulic system further comprises a manual oil supply mechanism, which is adapted to be connected with the fifth pipeline through a quick connector.

[0012] Optionally, a one-way flow structure is arranged between the accumulator and the first power mechanism and the second power mechanism, and the one-way flow structure is adapted to allow hydraulic oil to flow from the first power mechanism and the second power mechanism to the accumulator in one direction.

[0013] Optionally, a one-way throttle valve is arranged on the first pipeline and the second pipeline.

[0014] Optionally, the hydraulic system further comprises a safety valve, which is in communication with the oil inlet of the first reversing valve through an eighth pipeline.

[0015] The application further provides an engineering machine comprising the crawling ladder, which is driven by the above hydraulic system.

[0016] The application has the following advantages:

[0017] 1. According to the technical scheme of the application, the driving mechanism can be supplied with oil by the first power mechanism or the second power mechanism, thereby realizing a multi-power source combined driving mode of the crawling ladder and improving the driving efficiency of the crawling ladder. Meanwhile, the pressure relief mechanism causes the pressure maintaining assembly on the first pipeline to open, so that the hydraulic oil in the rodless cavity of the driving mechanism can flow back to the oil tank, and the crawling ladder can be lowered by its own gravity without consuming the energy of the first power mechanism and the second power mechanism, thereby achieving the effect of saving energy. Therefore, the technical scheme of the application solves the defects of low efficiency and large power consumption of the crawling ladder lifting driving mechanism of the super large excavator in the prior art.

[0018] 2. The power source of the first power mechanism is an engine, and the power source of the second power mechanism is a generator. When the engine of the engineering machine is running, the engine can be used to supply oil to drive the crawling ladder to rise or fall. When the engine of the engineering machine is stopped, the motor can be used to supply oil.

[0019] 3. The pressure relief mechanism comprises an accumulator and a manual reversing valve, so that the opening of the balance valve is realized without consuming additional electric energy.

[0020] 4. The manual pump is connected with the fifth pipeline through a quick connector, and the accumulator can be pressurized after being placed for a long time. BRIEF DESCRIPTION OF DRAWINGS

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the hydraulic system of the ladder of the present invention is shown; and

[0023] Figure 2 A schematic diagram of the ladder structure of the engineering machinery of the present invention is shown.

[0024] Explanation of reference numerals in the attached figures:

[0025] 1. Ladder; 10. Drive mechanism; 11. Rodless chamber; 12. Rod chamber; 20. First directional valve; 21. Working port; 22. Inlet; 30. First pipeline; 40. Second pipeline; 50. Pressure holding assembly; 51. Sequence valve; 60. First power mechanism; 70. Second power mechanism; 80. Third pipeline; 90. Fourth pipeline; 100. Motor; 110. Pressure relief mechanism; 111. Third power mechanism; 112. Second directional valve; 120. Fifth pipeline; 130. Shuttle valve; 131. First inlet; 132. Second inlet; 133. Outlet; 140. Sixth pipeline; 150. Seventh pipeline; 160. Manual oil supply mechanism; 170. Quick-connect structure; 180. One-way flow structure; 190. One-way throttle valve; 200. Safety valve; 210. Eighth pipeline. Detailed Implementation

[0026] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0028] In the description of the present application, it should be noted that unless specifically defined and limited otherwise, the terms "mounting", "connection", "connecting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0029] In addition, the technical features involved in the different embodiments of the application described below can be combined with each other as long as there is no conflict between them.

[0030] As shown in Figure 1 and Figure 2 The hydraulic system of the climbing ladder of the engineering machine of the embodiment includes a driving mechanism 10, a first reversing valve 20, a first power mechanism 60, a second power mechanism 70 and a pressure relief mechanism 110. The driving mechanism 10 is adapted to drive the climbing ladder 1 to ascend or descend. The working oil port 21 of the first reversing valve 20 is communicated with the rodless cavity 11 and the rod cavity 12 of the driving mechanism 10 through the first pipeline 30 and the second pipeline 40, and the first pipeline 30 is provided with a pressure maintaining assembly 50. The first power mechanism 60 and the second power mechanism 70 are respectively communicated with the oil inlet 22 of the first reversing valve 20 through the third pipeline 80 and the fourth pipeline 90. The pressure relief mechanism 110 is connected with the pressure maintaining assembly 50 through the fifth pipeline 120, and the pressure relief mechanism 110 is adapted to make the pressure maintaining assembly 50 in an open state.

[0031] By applying the technical solution of the embodiment, the driving mechanism 10 can be supplied with oil through the first power mechanism 60 or the second power mechanism 70, thereby realizing the driving mode of multi-power source combination of the climbing ladder 1 and improving the driving efficiency of the climbing ladder 1. At the same time, the pressure relief mechanism 110 makes the pressure maintaining assembly 50 on the first pipeline 30 open, so that the hydraulic oil in the rodless cavity 11 of the driving mechanism 10 can flow back to the oil tank, and the climbing ladder 1 descends by its own gravity without consuming the energy of the first power mechanism 60 and the second power mechanism 70, thereby achieving the effect of saving energy. Therefore, the technical solution of the embodiment solves the defects of low efficiency and large power consumption of the climbing ladder lifting driving mechanism of the super large excavator in the prior art.

[0032] It should be noted that the first power mechanism 60 and the second power mechanism 70 are used to drive the oil pump to pump oil, thereby realizing the oil supply of the hydraulic system. Further, an oil pump is also arranged on the third pipeline 80, and the first power mechanism 60 can drive the oil pump to pump oil, thereby realizing the oil supply of the driving mechanism 10. An oil pump is also arranged on the fourth pipeline 90, and the second power mechanism 70 can drive the oil pump to pump oil, thereby realizing the oil supply of the driving mechanism 10.

[0033] It should be noted that the above-mentioned "drive mechanism 10" is a drive cylinder in the embodiment, which includes a cylinder body and a piston rod, and the piston rod divides the cylinder body into a rodless cavity 11 and a rod cavity 12. Of course, other mechanisms capable of driving the ladder 1 to ascend or descend can also be used as the above-mentioned drive mechanism 10.

[0034] Further, in the technical solution of the embodiment, the power source of the first power mechanism 60 is an engine, and the power source of the second power mechanism 70 is a motor 100. When the engine of the engineering machinery is running, the drive mechanism 10 can be supplied with oil through the engine (driving the oil pump to pump oil) to drive the ladder 1 to ascend or descend. When the engine of the engineering machinery is stopped, the drive mechanism 10 can be supplied with oil through the motor 100 (driving the oil pump to pump oil). At the same time, when the engine of the engineering machinery is stopped and the ladder 1 needs to descend, the pressure relief mechanism 110 makes the pressure maintaining assembly 50 on the first pipeline 30 open, so that the hydraulic oil in the rodless cavity 11 of the drive mechanism 10 can flow back to the oil tank, and the ladder 1 descends by its own gravity without consuming the electric energy of the battery of the motor 100, thereby achieving the effect of saving electric quantity. Therefore, the technical solution of the embodiment solves the defects of low efficiency and large power consumption of the ladder ascending and descending drive mechanism of the super large excavator in the prior art.

[0035] Of course, other power sources in the engineering machinery can also be used as the power source of the first power mechanism 60 or the second power mechanism, and are not limited to the above-mentioned engine or motor 100.

[0036] It should be noted that the above-mentioned "drive mechanism 10" is a drive cylinder in the embodiment, which includes a cylinder body and a piston rod, and the piston rod divides the cylinder body into a rodless cavity 11 and a rod cavity 12. Of course, other mechanisms capable of driving the ladder 1 to ascend or descend can also be used as the above-mentioned drive mechanism 10. Figure 2 It can be seen that the upper end of the ladder 1 in the embodiment is hinged to the engineering machinery, and the lower end is a swing end. The push rod of the drive mechanism 10 is connected with the ladder 1. When the push rod of the drive mechanism 10 is extended, the ladder 1 can be driven to ascend, and when the push rod of the drive mechanism 10 is retracted, the ladder 1 can be driven to descend. Further, those skilled in the art can understand that the push rod of the drive mechanism 10 continuously maintains a compressed state and does not exist in a tension state.

[0037] It should be noted that the pressure maintaining assembly 50 in the embodiment has a pressure maintaining state and an open state. In the open state, the hydraulic oil can flow from the first pipeline 30 to the rodless cavity 11, but the hydraulic oil cannot flow back from the pressure maintaining assembly 50, thereby maintaining the pressure of the rodless cavity 11. When the pressure maintaining assembly 50 is in the open state, the hydraulic oil can flow bidirectionally in the rodless cavity 11.

[0038] The pressure maintaining assembly 50 can adopt conventional pressure maintaining hydraulic elements, such as balance valves, hydraulic control one-way valves, etc.

[0039] As shown above, since the push rod of the drive mechanism 10 is always under pressure, its rod chamber 12 does not need to maintain the load through a pressure-holding assembly. Of course, those skilled in the art can also install a pressure-holding assembly 50 on the second pipeline 40 according to actual needs.

[0040] It should be noted that the hydraulic oil pumped by the first power mechanism 60 comes from the main hydraulic system of the construction machinery, and the oil pump driven by the first power mechanism 60 is driven by the engine of the construction machinery. Therefore, during the operation of the engine of the construction machinery, the oil pump driven by the first power mechanism 60 can supply oil to the drive mechanism 10. Specifically, in this embodiment, the hydraulic oil pumped by the first power mechanism 60 comes from the pilot oil supply system of the main hydraulic system.

[0041] It should be noted that the power source of the second power mechanism 70 mentioned above is the motor 100, that is, the motor 100 drives the oil pump to pump oil, and the power supply of the motor 100 comes from the battery of the construction machinery. When the construction machinery stops, the motor 100 starts and drives the oil pump to supply oil, thereby supplying oil to the drive mechanism 10.

[0042] Preferably, a check valve is provided on both the third pipeline 80 and the fourth pipeline 90 to prevent hydraulic oil from flowing back to the oil pump and causing hydraulic shock.

[0043] Furthermore, combined Figure 1 As can be seen, the first directional valve 20 in this embodiment is a three-position four-way directional valve, which includes an inlet port 22, a return port, and two working ports 21. Preferably, the first directional valve 20 is an electrically controlled directional valve. Hydraulic oil pumped by the oil pump driven by the first power mechanism 60 or the second power mechanism 70 enters the first directional valve 20 through the inlet port 22, and the return oil exits from the return port of the first directional valve 20 (i.e.,...). Figure 1 The oil is discharged to the oil tank through the T-port. Depending on the position of the first directional valve 20, the working port 21 can be either the inlet or the outlet. The third pipeline 80 and the fourth pipeline 90 mentioned above are both connected to the inlet port 22, that is, they are arranged in parallel, so that the first power mechanism 60 and the second power mechanism 70 can supply oil to the drive mechanism 10 at the same time (of course, in some embodiments not shown, the first power mechanism 60 and the second power mechanism 70 can supply oil to the drive mechanism 10 simultaneously). Of the two working ports 21, one is connected to the rodless chamber 11 through the first pipeline 30, and the other is connected to the rod chamber 12 through the second pipeline 40. The above-mentioned three-position four-way directional valve is a conventional hydraulic component, which those skilled in the art can understand based on... Figure 1 The content shown allows you to understand the flow direction of hydraulic oil in each gear, so it will not be described in detail again.

[0044] Of course, in some embodiments not shown, the first directional valve 20 can also be other commonly used directional valves, as long as they can control the piston rod of the drive mechanism 10 to extend or retract.

[0045] Based on the above, the hydraulic system of the ladder in this embodiment has the following working states (for simplicity, the working states of the hydraulic system will be referred to as working state one, working state two, and working state three below):

[0046] 1. When the engine of construction machinery is running, the ladder needs to go up or down.

[0047] When motor 100 is not started, drive mechanism 10 is supplied with oil through first power mechanism 60. When first reversing valve 20 is in the right position, push rod of drive mechanism 10 extends, and ladder 1 rises. When first reversing valve 20 is in the left position, push rod of drive mechanism 10 retracts, and ladder 1 descends.

[0048] 2. When the engine of construction machinery stops, the ladder needs to be raised.

[0049] When motor 100 starts, drive mechanism 10 is supplied with oil through second power mechanism 70. When first reversing valve 20 is in the right position, push rod of drive mechanism 10 extends, and ladder 1 rises.

[0050] 3. When the engine of the construction machinery is stopped, the ladder needs to be lowered.

[0051] With motor 100 not running, the first directional valve 10 is in the neutral position. The pressure relief mechanism 110 keeps the pressure holding assembly 50 in the neutral position, allowing the hydraulic oil in the rodless chamber 11 to flow back to the oil tank through the first directional valve 20, and the ladder 1 descends under its own weight. Simultaneously, a portion of the hydraulic oil in the rodless chamber 11 is replenished into the rod chamber 12, thus preventing the rod chamber 12 from drawing in a vacuum.

[0052] like Figure 1 As shown, in the technical solution of this embodiment, the pressure holding component 50 is a balance valve, the balance valve includes a sequence valve 51 disposed on the first pipeline 30, the pressure relief mechanism 110 includes a third power mechanism 111 and a second reversing valve 112, and the fifth pipeline 120 is connected to the sequence valve 51.

[0053] Specifically, the balance valve is a common hydraulic component in engineering machinery, and its working process is briefly described here. When no hydraulic oil is supplied to the sequence valve 51, the hydraulic oil can only flow unidirectionally to the rodless chamber 11 through the check valve in the balance valve, thus maintaining the load. When hydraulic oil is supplied to the sequence valve 51, the sequence valve 51 is opened, and the hydraulic oil can flow back from the rodless chamber 11 to the oil tank.

[0054] Therefore, when the hydraulic system is in operating state three, the second directional valve 112 opens the fifth pipeline 120, and the hydraulic oil in the third power mechanism 111 flows into the sequence valve 51 through the fifth pipeline 120, thereby opening the balance valve. At this time, the hydraulic oil in the rodless chamber 11 can flow back to the oil tank, and the ladder 1 can descend by its own weight.

[0055] Preferably, the second directional valve 112 is a manual directional valve. Furthermore, the second directional valve 112 is a two-position four-way directional valve. The second directional valve 112 can be manually operated to switch positions, thus without consuming additional electrical energy.

[0056] Of course, in some embodiments not shown, the second directional valve 112 may also be an electrically controlled directional valve.

[0057] Preferably, the third power mechanism 111 is an accumulator. Specifically, when the hydraulic system is in working state three, the hydraulic oil for opening the sequence valve 51 comes from the accumulator, so the motor 100 does not need to be started to supply hydraulic oil to the sequence valve 51, thereby saving electrical energy.

[0058] like Figure 1 As shown, in this embodiment, a one-way flow structure 180 is provided between the accumulator and the first power mechanism 60 and the second power mechanism 70. The one-way flow structure 180 is adapted to allow hydraulic oil to flow unidirectionally from the first power mechanism 60 and the second power mechanism 70 to the accumulator. Specifically, when the first power mechanism 60 or the second power mechanism 70 is pumping oil, a portion of the hydraulic oil can flow into the fifth pipeline 120 through the one-way flow structure 180, thereby allowing the accumulator to store energy. Preferably, the hydraulic oil in the accumulator mainly comes from the energy stored during the operation of the first power mechanism 60.

[0059] Preferably, the one-way flow structure 180 is a one-way valve.

[0060] like Figure 1 As shown, in this embodiment, the hydraulic system further includes a manual oil supply mechanism 160, which is adapted to be connected to the fifth pipeline 120 via a quick-connect structure 170. Specifically, the manual oil supply mechanism 160 is a manual pump, and the quick-connect structure 170 is a quick-connect coupling. When the oil pressure in the accumulator is insufficient, the manual pump is connected to the fifth pipeline 120 via the quick-connect coupling, and the pump is manually operated to pump oil into the accumulator, thereby raising the pressure in the accumulator to a predetermined level.

[0061] In addition, a ball valve is also installed on the fifth pipeline 120. Figure 1 (Structure below the accumulator). When the accumulator needs maintenance, open the ball valve to release pressure from the accumulator.

[0062] like Figure 1As shown, in the technical solution of this embodiment, the hydraulic system also includes a shuttle valve 130, a fifth pipeline 120 connected to the first inlet 131 of the shuttle valve 130, a second inlet 132 of the shuttle valve 130 connected to the second pipeline 40 via a sixth pipeline 140, and an outlet 133 of the shuttle valve 130 connected to the sequence valve 51 via a seventh pipeline 150.

[0063] It should be noted that the shuttle valve 130 is a conventional hydraulic component, and its function is to selectively connect the two inlets and outlets. Therefore, the specific internal structure of the shuttle valve 130 will not be described in detail.

[0064] Combination Figure 1 As can be seen, when the hydraulic system is in operation and the ladder 1 is descending, hydraulic oil enters from the second inlet 132, while the first inlet 131 is closed. The hydraulic oil flows from the outlet 133 into the sequence valve 51, which in turn opens the balance valve. At this time, the hydraulic oil in the rodless chamber 11 can flow back into the oil tank.

[0065] Combination Figure 1 As can be seen, when the hydraulic system is in operating state three, hydraulic oil enters from the first inlet 131, while the second inlet 132 is closed. Hydraulic oil flows from the outlet 133 into the sequence valve 51, which in turn opens the balance valve. At this time, the hydraulic oil in the rodless chamber 11 can flow back into the oil tank.

[0066] like Figure 1 As shown, in the technical solution of this example, a one-way throttle valve 190 is provided on the first pipeline 30 and the second pipeline 40. The one-way throttle valve 190 is located between the drive mechanism 10 and the first reversing valve 20, and is used to regulate the return oil flow rate.

[0067] Of course, the one-way throttle valve 190 can also be replaced by other conventional speed control valves.

[0068] like Figure 1 As shown, in this embodiment, the hydraulic system further includes a safety valve 200, which is connected to the inlet 22 of the first directional valve 20 via an eighth pipeline 210. Specifically, the safety valve 200 is arranged in parallel with the first power mechanism 60 and the second power mechanism 70, and is used to limit the maximum pressure of the hydraulic system.

[0069] This embodiment also provides an engineering machine, including a ladder 1, which is driven by the aforementioned hydraulic system. In this embodiment, the engineering machine is an excavator, and preferably a super-large excavator. Of course, other conventional engineering machines, such as cranes, concrete pump trucks, etc., can also use the aforementioned hydraulic system of the ladder 1.

[0070] Based on the above description, this patent application has the following advantages:

[0071] 1. The application integrates engine power source, DC motor power source, accumulator power source, manual pump power source and other multi-power sources to provide power for the lifting of the ladder, meeting the requirements of the ladder lifting under different working conditions;

[0072] 2. In the engine stop state, the battery can be used as the power source to make the ladder retract;

[0073] 3. In the engine stop state, the weight of the ladder and the accumulator are used to provide power to make the ladder descend, without using the battery power, thereby reducing the consumption of the battery power;

[0074] 4. The manual pump can be used to provide power for the accumulator, solving the problem of insufficient pressure of the accumulator caused by long-term placement.

[0075] Obviously, the above embodiments are only examples for clearly illustrating, but not limiting the embodiments. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the embodiments are not required to be exhausted, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A hydraulic system for a ladder, comprising: Drive mechanism (10) is adapted to drive the ladder (1) to rise or fall; The first directional valve (20) has its working port (21) connected to the rodless chamber (11) of the drive mechanism (10) via a first pipeline (30). The working port (21) of the first directional valve (20) is connected to the rod chamber (12) of the drive mechanism (10) via a second pipeline (40). A pressure holding assembly (50) is provided on the first pipeline (30). The first power mechanism (60) and the second power mechanism (70) are connected to the oil inlet (22) of the first reversing valve (20) through the third pipeline (80) and the fourth pipeline (90), respectively. Both the first power mechanism (60) and the second power mechanism (70) can supply oil to the drive mechanism (10) to drive the ladder (1) to rise or fall. The pressure relief mechanism (110) is connected to the pressure holding assembly (50) via the fifth pipeline (120). The pressure relief mechanism (110) is adapted to open the pressure holding assembly (50) when the ladder (1) needs to descend, so that the hydraulic oil in the rodless chamber (11) flows back to the oil tank.

2. In the hydraulic system according to claim 1, the power source of the first power mechanism (60) is an engine, and the power source of the second power mechanism (70) is an electric motor.

3. The hydraulic system according to claim 1, wherein the pressure holding assembly (50) includes a sequence valve (51) disposed on the first pipeline (30), the pressure relief mechanism (110) includes a third power mechanism (111) and a second directional valve (112), and the fifth pipeline (120) is connected to the sequence valve (51).

4. The hydraulic system according to claim 3, wherein the hydraulic system further comprises a shuttle valve (130), the fifth pipeline (120) is connected to the first inlet (131) of the shuttle valve (130), the second inlet (132) of the shuttle valve (130) is connected to the second pipeline (40) through the sixth pipeline (140), and the outlet (133) of the shuttle valve (130) is connected to the sequence valve (51) through the seventh pipeline (150).

5. In the hydraulic system according to claim 3 or 4, the second directional valve (112) is a manual directional valve.

6. In the hydraulic system according to claim 3 or 4, the power source of the third power mechanism (111) is an accumulator.

7. The hydraulic system according to claim 6, the hydraulic system further comprising a manual oil supply mechanism (160), the manual oil supply mechanism (160) being adapted to be connected to the fifth pipeline (120) via a quick-connect fitting (170).

8. The hydraulic system according to claim 6, wherein a one-way flow structure (180) is provided between the accumulator and the first power mechanism (60) and the second power mechanism (70), the one-way flow structure (180) being adapted to allow hydraulic oil to flow unidirectionally from the first power mechanism (60) and the second power mechanism (70) to the accumulator.

9. The hydraulic system according to any one of claims 1 to 4, wherein the first pipeline (30) and the second pipeline (40) are provided with one-way throttle valves (190).

10. The hydraulic system according to any one of claims 1 to 4, the hydraulic system further comprising a safety valve (200) connected to the oil inlet (22) of the first directional valve (20) via an eighth pipeline (210).

11. An engineering machine, comprising a ladder (1) driven by a hydraulic system as claimed in any one of claims 1 to 10.

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