A forklift energy recovery system

Abstract

The present invention provides a forklift energy recovery system, comprising a hydraulic drive module, a hydraulic control module and an energy recovery module; the hydraulic drive module comprises a lifting cylinder group, a hydraulic power unit and a three-position six-way electromagnetic reversing valve, and the hydraulic power unit is connected to the lifting cylinder group through the three-position six-way electromagnetic reversing valve; the energy recovery module comprises a recovery cylinder group, a two-position two-way electromagnetic reversing valve, and a two-position three-way electromagnetic reversing valve; the inlet of the recovery cylinder group is connected to the inlet of the three-position six-way electromagnetic reversing valve through the two-position three-way electromagnetic reversing valve; the inlet of the recovery cylinder group is connected to the hydraulic power unit through the two-position two-way electromagnetic reversing valve; the hydraulic control module is used to recover energy during the load lowering process by selectively controlling the engagement of the three-position six-way electromagnetic reversing valve, the two-position two-way electromagnetic reversing valve and the two-position three-way electromagnetic reversing valve. The present invention can effectively improve the energy utilization rate of the forklift and the life of the hydraulic system components.

Description

Technical Field

[0001] The invention relates to the field of forklifts or energy conversion of lifting equipment, and in particular to an energy recovery system for a forklift. Background Art

[0002] With the rapid development of social economy, modern industrial logistics system has become the infrastructure to promote social development and economic construction, and it is of great significance to the formation of national economic scale and the development of modern industry. The types, frequency and scale of logistics in modern industrial logistics system are increasing rapidly. Therefore, the importance of loading and unloading is more significant. Forklifts are widely used in various places in the industrial transportation industry with their efficient handling capacity and strong operation flexibility. On the other hand, the energy crisis and the pressure of energy conservation and emission reduction are severe. The cause of energy conservation and environmental protection has vigorously promoted the transformation and upgrading of forklifts, and also put forward higher standards and requirements for the energy consumption of forklift hydraulic systems.

[0003] Traditional forklift hydraulic systems use a relief valve to directly release pressurized oil to the oil tank to achieve load reduction. This method causes huge energy losses and low energy efficiency for forklifts with heavy loads and frequent lifting. Therefore, it is necessary to design a new energy-saving forklift lifting system to reasonably recycle and reuse its lifting potential energy to achieve energy-saving transformation of forklifts.

[0004] The existing forklift energy recovery system usually uses hydraulic accumulators to save energy, but the technology is not yet mature, the energy recovery efficiency is difficult to guarantee, and the control is complex. The accumulator equipment is bulky, which affects the internal space layout of the forklift and the operational maneuverability of the entire vehicle. It is extremely unsuitable for installation and use on small forklifts. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a forklift energy recovery system, which can effectively improve the energy utilization rate of the forklift and the life of the hydraulic system components, and reduce the use cost of the forklift.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] A forklift energy recovery system comprises a hydraulic drive module, a hydraulic control module and an energy recovery module;

[0008] The hydraulic drive module includes a lifting cylinder group, a hydraulic power unit and a three-position six-way electromagnetic reversing valve. The lifting cylinder group is used to lift the load. The hydraulic power unit is connected to the lifting cylinder group through the three-position six-way electromagnetic reversing valve to make the lifting cylinder group rise and fall synchronously.

[0009] The energy recovery module includes a recovery cylinder group, a two-position two-way electromagnetic reversing valve, and a two-position three-way electromagnetic reversing valve; the recovery cylinder group is used to push the slider; the inlet of the recovery cylinder group is connected to the inlet of the three-position six-way electromagnetic reversing valve through the two-position three-way electromagnetic reversing valve; the inlet of the recovery cylinder group is connected to the hydraulic power unit through the two-position two-way electromagnetic reversing valve;

[0010] The hydraulic control module selectively controls the engagement of the three-position six-way solenoid reversing valve, the two-position two-way solenoid reversing valve and the two-position three-way solenoid reversing valve to connect the outlet of the lifting cylinder group with the inlet of the recovery cylinder group to recover energy during the load lowering process.

[0011] Furthermore, the hydraulic power unit includes an engine, a variable displacement hydraulic pump, a hydraulic oil tank and a second overflow valve, the engine is used to drive the variable displacement hydraulic pump, the inlet of the variable displacement hydraulic pump is connected to the hydraulic oil tank, and the outlet of the variable displacement hydraulic pump is equipped with a second overflow valve.

[0012] Furthermore, the interfaces of the three-position six-way solenoid reversing valve include port P, port T, port D, port A, port B and port C. The port P and port D are respectively connected to the hydraulic power unit, the port T is connected to the two-position three-way solenoid reversing valve, the port A and port C are respectively connected to the hydraulic oil tank, and the port B is connected to the lifting cylinder group.

[0013] Furthermore, the sliding block is a forklift balance block.

[0014] Furthermore, a first one-way valve is installed between the recovery cylinder group inlet and the two-position three-way electromagnetic reversing valve to prevent hydraulic oil from flowing from the recovery cylinder group to the two-position three-way electromagnetic reversing valve; and a first overflow valve is installed at the recovery cylinder group inlet.

[0015] Furthermore, the hydraulic control module includes a first pressure sensor, a second pressure sensor and a control console; the first pressure sensor is used to detect the working pressure of the lifting cylinder group, and the second pressure sensor is used to detect the working pressure of the recovery cylinder group; the control console selectively controls the engagement of the three-position six-way solenoid reversing valve, the two-position two-way solenoid reversing valve and the two-position three-way solenoid reversing valve according to the detection values ​​of the first pressure sensor and the second pressure sensor.

[0016] Furthermore, when a forklift is moving a load from a high place to a low place or when the forklift is descending without a load, if p r <p m And p l＞ p rWhen the control console controls the SB2 electromagnetic coil of the three-position six-way electromagnetic reversing valve to be energized, so that the A port is connected to the P port and the B port is connected to the T port respectively, and the control console controls the two-position three-way electromagnetic valve to connect the T port of the three-position six-way electromagnetic reversing valve to the recovery cylinder group, which is used to convert the potential energy released during the load or forklift's unloaded descent into the kinetic energy of the slider; wherein, p r is the detection value of the second pressure sensor; p m The set pressure of the first relief valve, p l is the detection value of the first pressure sensor;

[0017] When p r =p m or l ≤p r When the control console controls the SB2 electromagnetic coil of the three-position six-way electromagnetic reversing valve to be energized, so that the A port is connected to the P port and the B port is connected to the T port respectively; the control console controls the two-position three-way electromagnetic valve to be reset so that the T port of the three-position six-way electromagnetic reversing valve is connected to the hydraulic oil tank; the control console controls the two-position two-way electromagnetic reversing valve to be reset so that the inlet of the recovery cylinder group is connected to the inlet of the variable displacement hydraulic pump, so as to lower the load or the empty forklift to the target height.

[0018] Furthermore, when a forklift is moving a load from a low place to a high place or when the forklift is rising without a load, when p r >0, the console controls the SB1 electromagnetic coil of the three-position six-way electromagnetic reversing valve to be energized, so that port A is connected to port T and port B is connected to port P respectively, the console controls the two-position three-way electromagnetic valve to reset so that port T of the three-position six-way electromagnetic reversing valve is connected to the hydraulic oil tank, and the console controls the two-position two-way valve to connect the recovery cylinder group to the inlet of the variable displacement hydraulic pump, and the potential energy of the slider is converted into hydraulic energy, and the engine provides auxiliary power until the load or the forklift rises to the target height without load; when p r =0, the control console controls the SB1 electromagnetic coil of the three-position six-way electromagnetic reversing valve to be energized, so that port A is connected to port T and port B is connected to port P respectively, and the control console controls the two-position three-way electromagnetic valve to reset so that port T of the three-position six-way electromagnetic reversing valve is connected to the hydraulic oil tank, which is used to lift the load or forklift without load through the hydraulic power unit.

[0019] The beneficial effects of the present invention are:

[0020] 1. The forklift energy recovery system of the present invention can alleviate the problems of high fuel consumption and high emissions of traditional forklifts. It recovers the potential energy of goods and forks when the forklift moves goods and forks from a high place to a low place, and releases the recovered potential energy when the goods and forks are lifted, thereby improving the energy utilization efficiency of the forklift and reducing the use cost of the forklift.

[0021] 2. The forklift energy recovery system of the present invention recovers the potential energy of the forklift during the load lowering process through the slider, and the potential energy of the load is converted into the potential energy of the slider. The energy conversion path is short and the energy recovery efficiency is high.

[0022] 3. The forklift energy recovery system described in the present invention recovers the potential energy during the load lowering process through the slider, which reduces the throttling loss of the hydraulic valve compared with the traditional valve control system, avoids the overheating of the hydraulic system components due to throttling, increases the life of the hydraulic valve, reduces the leakage loss of the hydraulic system, and further improves the energy recovery efficiency.

[0023] 4. The forklift energy recovery system described in the present invention can select sliders of different weights to meet the needs of forklifts with different load requirements, and the product coverage is wide. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, it is obvious that other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the forklift energy recovery system of the present invention.

[0026] Figure 2 This is a load increase principle diagram of the present invention.

[0027] Figure 3 This is a schematic diagram of the load reduction energy recovery principle of the present invention.

[0028] Figure 4 This is a load reduction principle diagram of the present invention.

[0029] Figure 5 This is a schematic diagram of the principle of the slider descending to assist the load ascending according to the present invention.

[0030] In the figure:

[0031] 1-engine; 2-speed sensor; 3-ECU; 4-variable displacement hydraulic pump; 5-three-position six-way solenoid reversing valve; 6-hydraulic oil tank; 7-first lifting cylinder; 8-second lifting cylinder; 9-first pressure sensor; 10-load; 11-control console; 12-slider; 13-first recovery cylinder; 14-second recovery cylinder; 15-two-position two-way solenoid reversing valve; 16-second pressure sensor; 17-first one-way valve; 18-two-position three-way solenoid reversing valve; 20-second one-way valve; 22-first overflow valve; 23-second overflow valve. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0035] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] like Figure 1 As shown, the forklift energy recovery system of the present invention comprises a hydraulic drive module, a hydraulic control module and an energy recovery module;

[0037] The hydraulic drive module includes a first lifting cylinder 7, a second lifting cylinder 8, a hydraulic power unit and a three-position six-way electromagnetic reversing valve 5. The first lifting cylinder 7 and the second lifting cylinder 8 are respectively installed at the bottom of the load 10. The hydraulic power unit includes an engine 1, a variable displacement hydraulic pump 4, a hydraulic oil tank 6 and a second relief valve 23. The engine 1 is used to drive the variable displacement hydraulic pump 4. The inlet of the variable displacement hydraulic pump 4 is connected to the hydraulic oil tank 6. A second one-way valve 20 is installed between the inlet of the variable displacement hydraulic pump 4 and the hydraulic oil tank 6. A second relief valve 23 is installed at the outlet of the variable displacement hydraulic pump 4. A speed sensor 2 is installed on the input shaft of the variable displacement hydraulic pump 4 to detect the speed of the variable displacement hydraulic pump 4. The interfaces of the three-position six-way electromagnetic reversing valve 5 include a P port, a T port, a D port, an A port, a B port and a C port. The P port and the D port are respectively connected to the hydraulic power unit, the T port is connected to the two-position three-way electromagnetic reversing valve 18, the A port and the C port are respectively connected to the hydraulic oil tank 6, and the B port is respectively connected to the first lifting cylinder 7 and the second lifting cylinder 8. The first lifting cylinder 7 and the second lifting cylinder 8 can be regarded as connected in parallel between the B port and the load 10. The hydraulic power unit is connected to the first lifting cylinder 7 and the second lifting cylinder 8 through the three-position six-way electromagnetic reversing valve 5, so as to make the first lifting cylinder 7 and the second lifting cylinder 8 rise and fall synchronously;

[0038] The energy recovery module includes a first recovery cylinder 13, a second recovery cylinder 14, a two-position two-way electromagnetic reversing valve 15, and a two-position three-way electromagnetic reversing valve 18; the first recovery cylinder 13 and the second recovery cylinder 14 are used to simultaneously push the slider 12 to lift, and the slider 12 is a forklift balance block; the inlets of the first recovery cylinder 13 and the second recovery cylinder 14 are connected to the T port of the three-position six-way electromagnetic reversing valve 5 through the two-position three-way electromagnetic reversing valve 18; the inlets of the first recovery cylinder 13 and the second recovery cylinder 14 are connected to the inlet of the variable displacement hydraulic pump 4 through the two-position two-way electromagnetic reversing valve 15; a first check valve 17 is installed between the inlet of the first recovery cylinder 13 and the second recovery cylinder 14 and the two-position three-way electromagnetic reversing valve 18 to prevent the hydraulic oil from the first recovery cylinder 13 and the second recovery cylinder 14 from flowing to the two-position three-way electromagnetic reversing valve 18; a first overflow valve 22 is installed at the inlet of the first recovery cylinder 13 and the second recovery cylinder 14.

[0039] The hydraulic control module includes a first pressure sensor 9, a second pressure sensor 16, an ECU 3 and a control console 11; the first pressure sensor 9 is used to detect the working pressure of the lifting cylinder group 7, 8, and the second pressure sensor 16 is used to detect the working pressure of the recovery cylinder group 13, 14; the control console 11 selectively controls the engagement of the three-position six-way electromagnetic reversing valve 5, the two-position two-way electromagnetic reversing valve 15 and the two-position three-way electromagnetic reversing valve 18 according to the detection values ​​of the first pressure sensor 9 and the second pressure sensor 16, so that the outlet of the lifting cylinder group is connected to the inlet of the recovery cylinder group, so as to recover the energy of the load 10 during the lowering process. The ECU 3 is used to control the engine 1, and the control console 11 sends instructions to the ECU 3.

[0040] The following analyzes four typical operating conditions of forklift load reduction, unloaded reduction, load increase, and unloaded increase as embodiments to specifically describe the operation mode of the forklift potential energy recovery system. The embodiments are used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above-mentioned contents of the present invention also fall within the scope of protection of the present invention.

[0041] like Figure 3 As shown, when a forklift is moving a load from a high place to a low place or when the forklift is descending empty, if p r <p m And p l＞ p r When the control console 11 controls the SB2 electromagnetic coil of the three-position six-way electromagnetic reversing valve 5 to be energized, so that the A port is connected to the P port and the B port is connected to the T port respectively, and the control console 11 controls the two-position three-way electromagnetic valve 18 to connect the T port of the three-position six-way electromagnetic reversing valve 5 to the first recovery cylinder 13 and the second recovery cylinder 14, so as to convert the potential energy released during the unloaded descent of the load 10 or the forklift into the kinetic energy of the slider 12; wherein, p r is the detection value of the second pressure sensor 16; p m The pressure of the first relief valve 22 is set, p l is the detection value of the first pressure sensor 9; when p r =p m or l ≤p r When the control console 11 controls the SB2 electromagnetic coil of the three-position six-way electromagnetic reversing valve 5 to be energized, so that the A port is connected to the P port and the B port is connected to the T port respectively. The control console 11 controls the two-position three-way electromagnetic valve 18 to reset so that the T port of the three-position six-way electromagnetic reversing valve 5 is connected to the hydraulic oil tank 6, so as to lower the load 10 or the empty forklift to the target height. Figure 4 shown.

[0042] like Figure 2As shown, when the forklift is moving a load from a low place to a high place or when the forklift is rising empty, when p r >0, the control console 11 controls the SB1 electromagnetic coil of the three-position six-way electromagnetic reversing valve 5 to be energized, so that the A port is connected to the T port and the B port is connected to the P port respectively, and the control console 11 controls the two-position three-way electromagnetic valve 18 to reset so that the T port of the three-position six-way electromagnetic reversing valve 5 is connected to the hydraulic oil tank 6, and the control console 11 controls the two-position two-way valve 15 to connect the first recovery cylinder 13 and the second recovery cylinder 14 to the inlet of the variable displacement hydraulic pump 4, and the potential energy of the slider 12 is converted into hydraulic energy, and the engine 1 provides auxiliary power until the load 10 or the forklift rises to the target height without load; when p r =0, the control console 11 controls the SB1 electromagnetic coil of the three-position six-way electromagnetic reversing valve 5 to be energized, so that the A port is connected to the T port and the B port is connected to the P port respectively, and the control console 11 controls the two-position three-way electromagnetic valve 18 to reset so that the T port of the three-position six-way electromagnetic reversing valve 5 is connected to the hydraulic oil tank 6, so as to make the load 10 or the forklift empty-load rise through the hydraulic power unit, such as Figure 5 shown.

[0043] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0044] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A forklift energy recovery system, characterized in that: It includes a hydraulic drive module, a hydraulic control module and an energy recovery module; The hydraulic drive module comprises a lifting cylinder group (7, 8), a hydraulic power unit and a three-position six-way electromagnetic reversing valve (5); the lifting cylinder group (7, 8) is used to lift and lower a load (10); the hydraulic power unit is connected to the lifting cylinder group (7, 8) via the three-position six-way electromagnetic reversing valve (5) and is used to make the lifting cylinder group (7, 8) rise and fall synchronously; The energy recovery module comprises a recovery cylinder group (13, 14), a two-position two-way electromagnetic reversing valve (15), and a two-position three-way electromagnetic reversing valve (18); the recovery cylinder group (13, 14) is used to push the slider (12); the inlet of the recovery cylinder group (13, 14) is connected to the inlet of the three-position six-way electromagnetic reversing valve (5) through the two-position three-way electromagnetic reversing valve (18); the inlet of the recovery cylinder group (13, 14) is connected to the hydraulic power unit through the two-position two-way electromagnetic reversing valve (15); The hydraulic control module selectively controls the engagement of a three-position six-way electromagnetic reversing valve (5), a two-position two-way electromagnetic reversing valve (15) and a two-position three-way electromagnetic reversing valve (18) so that the outlet of the lifting cylinder group (7, 8) is connected to the inlet of the recovery cylinder group (13, 14), thereby recovering energy during the lowering process of the load (10).

2. The forklift energy recovery system according to claim 1, characterized in that: The hydraulic power unit comprises an engine (1), a variable displacement hydraulic pump (4), a hydraulic oil tank (6) and a second relief valve (23); the engine (1) is used to drive the variable displacement hydraulic pump (4); the inlet of the variable displacement hydraulic pump (4) is connected to the hydraulic oil tank (6); and the outlet of the variable displacement hydraulic pump (4) is provided with a second relief valve (23).

3. The forklift energy recovery system according to claim 1, characterized in that: The interfaces of the three-position six-way electromagnetic reversing valve (5) include a P port, a T port, a D port, an A port, a B port and a C port, wherein the P port and the D port are respectively connected to the hydraulic power unit, the T port is connected to the two-position three-way electromagnetic reversing valve (18), the A port and the C port are respectively connected to the hydraulic oil tank (6), and the B port is connected to the lifting cylinder group (7, 8).

4. The forklift energy recovery system according to claim 1, characterized in that: The sliding block (12) is a forklift balancing block.

5. The forklift energy recovery system according to claim 1, characterized in that: A first check valve (17) is installed between the inlet of the recovery cylinder group (13, 14) and the two-position three-way electromagnetic reversing valve (18) to prevent hydraulic oil from flowing from the recovery cylinder group (13, 14) to the two-position three-way electromagnetic reversing valve (18); a first overflow valve (22) is installed at the inlet of the recovery cylinder group (13, 14).

6. The forklift energy recovery system according to claim 3, characterized in that: The hydraulic control module comprises a first pressure sensor (9), a second pressure sensor (16) and a control console (11); the first pressure sensor (9) is used to detect the working pressure of the lifting cylinder group (7, 8), and the second pressure sensor (16) is used to detect the working pressure of the recovery cylinder group (13, 14); the control console (11) selectively controls the engagement of the three-position six-way electromagnetic reversing valve (5), the two-position two-way electromagnetic reversing valve (15) and the two-position three-way electromagnetic reversing valve (18) according to the detection values ​​of the first pressure sensor (9) and the second pressure sensor (16).

7. The forklift energy recovery system according to claim 6, characterized in that: When a forklift is moving a load from a high place to a low place or when the forklift is descending without a load, p r <p m and p l＞ p r When the control console (11) controls the SB2 electromagnetic coil of the three-position six-way electromagnetic reversing valve (5) to be energized, so that the A port is connected to the P port and the B port is connected to the T port respectively, and the control console (11) controls the two-position three-way electromagnetic reversing valve (18) to connect the T port of the three-position six-way electromagnetic reversing valve (5) to the recovery cylinder group (13, 14), so as to convert the potential energy released during the load (10) or the forklift's unloaded descent into the kinetic energy of the slider (12); wherein, p r is the detection value of the second pressure sensor (16); p m Set the pressure of the first relief valve (22), p l is the detection value of the first pressure sensor (9); when p r =p m or p l ≤ p r When the control console (11) controls the SB2 electromagnetic coil of the three-position six-way electromagnetic reversing valve (5) to be energized, so that the A port is connected to the P port and the B port is connected to the T port respectively; the control console (11) controls the two-position three-way electromagnetic reversing valve (18) to be reset so that the T port of the three-position six-way electromagnetic reversing valve (5) is connected to the hydraulic oil tank (6); the control console (11) controls the two-position two-way electromagnetic reversing valve (15) so that the inlet of the recovery cylinder group (13, 14) is connected to the inlet of the variable displacement hydraulic pump (4), so as to lower the load (10) or the empty forklift to the target height.

8. The forklift energy recovery system according to claim 7, characterized in that: When a forklift is moving a load from a low place to a high place or when the forklift is ascending without a load, p r > 0 When the control console (11) controls the SB1 electromagnetic coil of the three-position six-way electromagnetic reversing valve (5) to be energized, so that the A port is connected to the T port and the B port is connected to the P port respectively; the control console (11) controls the two-position three-way electromagnetic reversing valve (18) to reset so that the T port of the three-position six-way electromagnetic reversing valve (5) is connected to the hydraulic oil tank (6); the control console (11) controls the two-position two-way electromagnetic reversing valve (15) to connect the recovery cylinder group (13, 14) with the inlet of the variable displacement hydraulic pump (4), and the potential energy of the slider (12) is converted into hydraulic energy, and the engine (1) provides auxiliary power until the load (10) or the forklift without load rises to the target height; when p r =0 When the control console (11) controls the SB1 electromagnetic coil of the three-position six-way electromagnetic reversing valve (5) to be energized, so that the A port is connected to the T port and the B port is connected to the P port respectively. The control console (11) controls the two-position three-way electromagnetic reversing valve (18) to be reset so that the T port of the three-position six-way electromagnetic reversing valve (5) is connected to the hydraulic oil tank (6), so as to make the load (10) or the forklift empty-loaded rise through the hydraulic power unit.

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