Variable-frequency tensioning device for belt conveyor

Abstract

The utility model discloses a frequency conversion tensioning device for a belt conveyor, which comprises a frequency conversion motor, a brake, a controller, a winding drum, a speed reducer, a steel wire rope, a pulley, a tensioning trolley, an adhesive tape, a buffer oil cylinder and a hydraulic system, the adhesive tape is wound on a turnabout drum of the tensioning trolley, and the pulley is connected to the other side of the tensioning trolley. One end of the brake is connected with the power output end of the variable frequency motor through a coupler I, and the other end of the brake is connected with an input shaft of the speed reducer through a coupler II; one end of the steel wire rope is fixedly connected with the winding drum and wound on the winding drum, and the other end of the steel wire rope bypasses the pulley and is connected with the movable end of the buffering oil cylinder which is connected with the brake through the hydraulic system. And the brake is connected with the controller through a plurality of groups of oil pipes. The tension fluctuation of the rubber belt can be effectively absorbed, the service life of the steel wire rope is prolonged, braking can be enhanced, the tension of the steel wire rope is prevented from being reduced under the reverse tension of the rubber belt, and frequent tensioning is avoided.

Description

Technical Field

[0001] The utility model belongs to the technical field of belt conveyor tensioning, and particularly relates to a variable-frequency tensioning device for belt conveyors. Background Art

[0002] At present, there are various forms of belt conveyor tensioning devices, such as weight tensioning, winch tensioning, and hydraulic tensioning. Since different tension forces are required for the belt during startup and operation, and weight tensioning can only provide one kind of tension force, its application is becoming less and less. Hydraulic tensioning can meet the requirements of different tension forces during startup and operation, but the reaction speed of the hydraulic tensioning system is relatively slow. When the belt tension force decreases and the tension force needs to be increased, the electric winch or hydraulic winch equipped with the hydraulic tensioning device rotates slowly, which cannot meet the requirements of rapid response of modern belt conveyors.

[0003] Patent CN200810170260.8 discloses a variable-frequency tensioning device. This device actually belongs to winch tensioning, but only uses a variable-frequency motor. This device has a fast reaction speed and can keep up with the rapid response requirements of belt conveyors. However, this device has two problems: one is that this device is directly connected to the belt conveyor tensioning trolley with a steel wire rope, which belongs to a rigid connection and has no buffer component, and cannot effectively absorb the tension fluctuation of the belt, which is not conducive to extending the service life of the steel wire rope; the other is that there is no clear design for the winch brake. Generally, after tensioning, the winch needs to be quickly braked to ensure that the steel wire rope will not loosen under the reverse tension of the belt, thereby reducing the belt tension force and avoiding frequent tensioning. Content of the Utility Model

[0004] The purpose of the utility model is to provide a variable-frequency tensioning device for belt conveyors, which can effectively absorb the tension fluctuation of the belt, extend the service life of the steel wire rope, and at the same time can strengthen the braking to prevent the tension of the steel wire rope from decreasing under the reverse tension of the belt, and avoid frequent tensioning.

[0005] To achieve the above purpose, the variable-frequency tensioning device for belt conveyors of the utility model includes a variable-frequency motor, a brake, a controller, a drum, a reducer, a steel wire rope, a pulley, a tensioning trolley, a belt, a buffer oil cylinder and a hydraulic system. The belt is wound around the redirecting roller of the tensioning trolley, and the pulley is connected to the other side of the tensioning trolley. One end of the brake is connected to the power output end of the variable-frequency motor through coupling Ⅰ, and the other end is connected to the input shaft of the reducer through coupling Ⅱ. The output shaft of the reducer is connected to the drum;

[0006] One end of the steel wire rope is fixedly connected to the drum and wound around the drum, and the other end passes around the pulley and is connected to the movable end of the buffer oil cylinder. The buffer oil cylinder is connected to the brake through the hydraulic system;

[0007] The brake is connected to the controller through multiple groups of oil pipes.

[0008] As a further solution of the present utility model: The brake includes a brake housing, on which a brake shaft is provided. The two ends of the brake shaft extend out of the brake housing and are respectively connected to a variable-frequency motor and a speed reducer through coupling Ⅰ and coupling Ⅱ;

[0009] Inside the brake housing, a brake piston slidably sleeved on the brake shaft is provided. One end of the brake piston is connected with a brake spring sleeved on the brake shaft, and the other end of the brake spring is connected to the end plate of the brake housing;

[0010] One end of the brake housing far from the brake spring is connected with a static friction plate, and a dynamic friction plate matched with the static friction plate is provided on the brake shaft;

[0011] One end of the brake housing close to the brake spring is provided with a brake oil port Ⅰ, one end close to the static friction plate is provided with a brake oil port Ⅱ, and a brake oil port Ⅲ connecting the hydraulic system is provided between the brake piston and the static friction plate.

[0012] As a further solution of the present utility model: The controller includes a controller housing, inside which a controller piston and a tapered valve core are connected. The large end face of the tapered valve core is connected with a large spring, and the other end of the large spring is connected to the end face of the controller housing;

[0013] A control valve core is sleeved inside the tapered valve core. The control valve core is in dynamic connection with the end face shaft hole of the controller piston. The end face of the control valve core is connected with a small spring, and the small spring is sleeved inside the large spring and the other end is connected to the end face of the controller housing;

[0014] On the end face of the controller housing close to the controller piston, a controller oil port Ⅰ is provided. A controller oil port Ⅱ is provided between the controller piston and the tapered valve core, and a controller oil port Ⅲ is provided on the end face connected with the large spring.

[0015] As a further solution of the present utility model: The brake oil port Ⅰ is communicated with the controller oil port Ⅱ through a pipeline, and the brake oil port Ⅱ is communicated with the controller oil port Ⅰ and the controller oil port Ⅲ through pipelines.

[0016] As a further solution of the present utility model: The buffer oil cylinder includes a cylinder barrel, inside which an oil cylinder piston is provided. A piston rod is connected to the oil cylinder piston, and the other end of the piston rod extends out of the cylinder barrel and is connected with a steel wire rope. A displacement sensor is connected to the piston rod, and the other end of the displacement sensor passes through the oil cylinder piston and extends out of one end of the cylinder barrel. An oil cylinder oil port connecting the hydraulic system is provided on the cylinder barrel close to the piston rod.

[0017] As a further solution of the utility model: the hydraulic system includes a gear pump and a pump station motor fixedly connected thereto, the gear pump outlet is connected to an electromagnetic reversing valve I, and the gear pump outlet is connected to a relief valve II, and the electromagnetic reversing valve I oil outlet is divided into two ways and connected to a check valve I and a check valve II respectively;

[0018] The outlet of the check valve I is connected to the oil port of the oil cylinder, and the outlet of the check valve I is also connected to the pressure transmitter I and the relief valve I;

[0019] The oil outlet of the check valve II is connected to the brake oil port III, and the oil outlet of the check valve II is also connected to the pressure transmitter II and the electromagnetic reversing valve II;

[0020] The oil outlet of relief valve I, the oil outlet of relief valve II, the oil suction port of the gear pump, the oil outlet and the oil return port of the electromagnetic reversing valve II are all connected to the oil tank.

[0021] Compared with the prior art, the beneficial effects of the utility model are as follows:

[0022] Using a buffer cylinder to connect the wire rope can buffer the tension fluctuation of the belt, reduce the peak tension, and extend the service life of the wire rope;

[0023] The brake can be used to achieve rapid braking, preventing the tension of the wire rope from decreasing under the reverse pulling force of the tape, thereby avoiding frequent tensioning;

[0024] The hydraulic system can make the variable frequency tensioning device of the belt conveyor work in an integral manner, thereby improving the effect of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The utility model is a structural schematic diagram of a variable frequency tensioning device for a belt conveyor.

[0026] Figure 2 The utility model is a structural schematic diagram of a brake in a variable frequency tensioning device for a belt conveyor.

[0027] Figure 3 The utility model is a schematic diagram of the structure of a controller in a variable frequency tensioning device for a belt conveyor.

[0028] Figure 4 The utility model is a structural schematic diagram of a buffer oil cylinder in a variable frequency tensioning device for a belt conveyor.

[0029] In the figure: 1. Variable-frequency motor; 2. Coupling I; 3. Brake; 4. Controller; 5. Coupling II; 6. Drum; 7. Reducer; 8. Steel wire rope; 9. Pulley; 10. Tensioning trolley; 11. Belt; 12. Buffer oil cylinder; 13. Pressure transmitter I; 14. Relief valve I; 15. Check valve I; 16. Relief valve II; 17. Gear pump; 18. Pump station motor; 19. Electromagnetic directional valve I; 20. Electromagnetic directional valve II; 21. Oil tank; 22. Check valve II; 23. Pressure transmitter II;

[0030] 3-1. Brake shaft; 3-2. Brake spring; 3-3. Brake housing; 3-4. Brake piston; 3-5. Moving friction plate; 3-6. Static friction plate; 3-A. Brake oil port I; 3-B. Brake oil port II; 3-C. Brake oil port III;

[0031] 4-1. Controller housing; 4-2. Controller piston; 4-3. Cone valve core; 4-4. Large spring; 4-5. Small spring; 4-6. Control valve core; 4-A. Controller oil port I; 4-B. Controller oil port II; 4-C. Controller oil port III;

[0032] 12-1. Cylinder barrel; 12-2. Oil cylinder piston; 12-3. Displacement sensor; 12-4. Piston rod; 12-A. Oil cylinder oil port. Detailed implementation mode

[0033] The present utility model will be further described below in conjunction with the accompanying drawings.

[0034] As Figure 1 shown, the variable-frequency tensioning device for a belt conveyor includes a variable-frequency motor 1, a brake 3, a controller 4, a drum 6, a reducer 7, a steel wire rope 8, a pulley 9, a tensioning trolley 10, a belt 11, a buffer oil cylinder 12 and a hydraulic system. The belt 11 is wound around the redirecting roller of the tensioning trolley 10. The pulley 9 is connected to the other side of the tensioning trolley 10. One end of the brake 3 is connected to the power output end of the variable-frequency motor 1 through the coupling I 2, and the other end is connected to the input shaft of the reducer 7 through the coupling II 5. The output shaft of the reducer 7 is connected to the drum 6;

[0035] One end of the steel wire rope 8 is fixedly connected to the drum 6 and wound around the drum 6, and the other end passes around the pulley 9 and is connected to the movable end of the buffer oil cylinder 12. The buffer oil cylinder 12 is connected to the brake 3 through the hydraulic system;

[0036] The brake 3 and the controller 4 are connected through multiple groups of oil pipes.

[0037] One end of the steel wire rope 8 is connected to the buffer oil cylinder 12, which plays a buffering role in the tension fluctuation of the belt 11 and can reduce the tension peak. When the tension of the belt 11 is too large, the hydraulic oil in the buffer oil cylinder 12 enters the hydraulic system for buffering regulation and quickly brakes through the brake 3 to prevent the tension of the steel wire rope 8 from decreasing under the reverse pulling force of the belt 11.

[0038] In order to make the brake 3 achieve a good braking effect, further, as Figure 2 shown, the brake 3 includes a brake housing 3-3. A brake shaft 3-1 is provided on the brake housing 3-3. Both ends of the brake shaft 3-1 extend out of the brake housing 3-3 and are respectively connected to the frequency conversion motor 1 and the reducer 7 through the coupling Ⅰ2 and the coupling Ⅱ5;

[0039] A brake piston 3-4 that is slidably sleeved on the brake shaft 3-1 is arranged inside the brake housing 3-3. One end of the brake piston 3-4 is connected with a brake spring 3-2 that sleeves the brake shaft 3-1, and the other end of the brake spring 3-2 is connected to the end plate of the brake housing 3-3;

[0040] A static friction plate 3-6 is connected to one end of the brake housing 3-3 away from the brake spring 3-2, and a dynamic friction plate 3-5 that cooperates with the static friction plate 3-6 is provided on the brake shaft 3-1;

[0041] A brake oil port Ⅰ3-A is provided at one end of the brake housing 3-3 close to the brake spring 3-2, a brake oil port Ⅱ3-B is provided at one end close to the static friction plate 3-6, and a brake oil port Ⅲ3-C connecting the hydraulic system is provided between the brake piston 3-4 and the static friction plate 3-6.

[0042] The dynamic friction plate 3-5 is slidably matched with the brake shaft 3-1, and the static friction plate 3-6 is slidably matched with the brake housing 3-3. Under the elastic force of the brake spring 3-2, the brake piston 3-4 is pushed to move the dynamic friction plate 3-5 and the static friction plate 3-6 to the end of the brake housing 3-3 to achieve braking by using friction.

[0043] In order to cooperate with the operation of the brake 3, further, as Figure 3 shown, the controller 4 includes a controller housing 4-1. A controller piston 4-2 and a tapered valve core 4-3 are connected inside the controller housing 4-1. A large spring 4-4 is connected to the large end face of the tapered valve core 4-3, and the other end of the large spring 4-4 is connected to the end face of the controller housing 4-1;

[0044] A control valve core 4-6 is sleeved inside the tapered valve core 4-3. The control valve core 4-6 is in dynamic connection with the end face shaft hole of the controller piston 4-2. A small spring 4-5 is connected to the end face of the control valve core 4-6. The small spring 4-5 is sleeved inside the large spring 4-4 and the other end is connected to the end face of the controller housing 4-1;

[0045] On the end face of the controller housing 4-1 close to the controller piston 4-2, there is a controller oil port I 4-A. Between the controller piston 4-2 and the cone valve core 4-3, there is a controller oil port II 4-B. On the end face connected to the large spring 4-4, there is a controller oil port III 4-C.

[0046] Furthermore, as Figure 1 shown, the brake oil port I 3-A is connected to the controller oil port II 4-B through a pipeline. The brake oil port II 3-B is connected to the controller oil port I 4-A and the controller oil port III 4-C through pipelines. This connects the brake 3 and the controller 4 to form a circuit.

[0047] Furthermore, as Figure 4 shown, the buffer oil cylinder 12 includes a cylinder barrel 12-1. Inside the cylinder barrel 12-1, there is an oil cylinder piston 12-2. A piston rod 12-4 is connected to the oil cylinder piston 12-2. The other end of the piston rod 12-4 extends out of the cylinder barrel 12-1 and is connected to the steel wire rope 8. A displacement sensor 12-3 is connected to the piston rod 12-4. The other end of the displacement sensor 12-3 passes through the oil cylinder piston 12-2 and extends out of one end of the cylinder barrel 12-1. On one end of the cylinder barrel 12-1 close to the piston rod 12-4, there is an oil cylinder oil port 12-A connected to the hydraulic system. When the tension of the belt 11 is too large, the hydraulic oil in the buffer oil cylinder 12 will enter the hydraulic system. The reduction of the hydraulic oil will cause the piston rod 12-4 to extend outwards. When the displacement sensor 12-3 detects that the outward extension amount of the piston rod 12-4 exceeds a certain value, the hydraulic system will supply oil to the buffer oil cylinder 12 to make the piston rod 12-4 retract, thereby achieving the buffering effect on the tension fluctuation of the belt 11.

[0048] In order to achieve the overall linkage effect of the device oil circuit and facilitate regulation, furthermore, as Figure 1 shown, the hydraulic system includes a gear pump 17 and its fixedly connected pump station motor 18. The outlet of the gear pump 17 is connected to the electromagnetic directional valve I 19. At the same time, the outlet of the gear pump 17 is paralleled with the overflow valve II 16. The oil outlet of the electromagnetic directional valve I 19 is divided into two paths and is respectively connected to the check valve I 15 and the check valve II 22;

[0049] The outlet of the check valve I 15 is connected to the oil cylinder oil port 12-A. At the same time, the outlet of the check valve I 15 is paralleled with the pressure transmitter I 13 and the overflow valve I 14;

[0050] The outlet of the check valve II 22 is connected to the brake oil port III 3-C. At the same time, the outlet of the check valve II 22 is paralleled with the pressure transmitter II 23 and the electromagnetic directional valve II 20;

[0051] The oil outlets of the overflow valve I 14, the overflow valve II 16, the oil suction port of the gear pump 17, the oil outlet and the return oil port of the electromagnetic directional valve II 20 are all connected to the fuel tank 21.

[0052] When the utility model is in specific use: One end of the steel wire rope 8 is connected to the buffer oil cylinder 12, which plays a buffering role in the tension fluctuation of the belt 11 and can reduce the tension peak value. When the tension of the belt 11 is too large, the hydraulic oil in the buffer oil cylinder 12 flows back to the oil tank 21 through the overflow valve I 14. The reduction of the hydraulic oil will cause the piston rod 12-4 to extend. When the displacement sensor 12-3 detects that the extension amount of the piston rod 12-4 exceeds a certain value, the hydraulic system starts the gear pump 17 to replenish oil to the buffer oil cylinder 12, so that the piston rod 12-4 retracts.

[0053] The brake 3 implements braking by using the frictional force between the moving friction plate 3-5 and the static friction plate 3-6. Under the action of the brake spring 3-2, the moving friction plate 3-5 and the static friction plate 3-6 can be quickly engaged, that is, rapid braking is realized, preventing the tension of the steel wire rope 8 from decreasing under the reverse pulling force of the belt.

[0054] When the drum 6 needs to wind the rope, before the frequency conversion motor 1 starts, the gear pump 17 starts first, provides hydraulic oil to the brake 3 through the electromagnetic directional valve I 19 and the check valve II 22. The brake piston 3-4 moves left under the action of the hydraulic oil, compressing the brake spring 3-2. The hydraulic oil at the brake spring 3-2 inside the brake housing 3-3 enters the controller 4 through the brake oil port I 3-A and the brake oil port II 4-B, pushing the cone valve core 4-3 to move right, so that the hydraulic oil can pass through the controller oil port III 4-C and the brake oil port II 3-B into the position where the moving friction plate 3-5 and the static friction plate 3-6 are located inside the brake housing 3-3, playing a lubricating role for the moving friction plate 3-5 and the static friction plate 3-6. Under the action of the large spring 4-4, the cone valve core 4-3 of the controller 4 can prevent the reverse flow of the hydraulic oil, that is, prevent the reduction of the hydraulic oil, thereby reducing the lubrication effect.

[0055] During braking, the brake piston 3-4 moves right under the action of the brake spring 3-2, and the hydraulic oil pressure at the moving friction plate 3-5 and the static friction plate 3-6 increases. The hydraulic oil enters the controller 4 simultaneously through the controller oil port I 4-A and the controller oil port III 4-C. The hydraulic oil entering the controller 4 through the controller oil port I 4-A pushes the controller piston 4-2 to move right, and the controller piston 4-2 then pushes the control valve core 4-6. Since the acting area of the controller piston 4-2 is much larger than the acting area of the control valve core 4-6, the control valve core 4-6 moves right, and the hydraulic oil entering through the controller oil port III 4-C flows back to the position of the brake spring 3-2 inside the brake housing 3-3 through the controller oil port II 4-B.

[0056] When the drum 6 finishes winding the rope and braking is required, the gear pump 17 stops operating, and the hydraulic oil inside the brake 3 flows back to the oil tank 21 through the electromagnetic directional valve II 20. Under the action of the brake spring 3-2, the brake piston 3-4 moves to the right, pushing the moving friction plate 3-5 to combine with the static friction plate 3-6. At the same time, the hydraulic oil between the moving friction plate 3-5 and the static friction plate 3-6 flows back to the position of the brake spring 3-2 inside the brake housing 3-3 through the controller 4, preventing the reduction of the friction force between the moving friction plate 3-5 and the static friction plate 3-6 due to excessive hydraulic oil, that is, preventing the reduction of the braking torque.

Claims

1. Variable-frequency tensioning device for belt conveyor, comprising a variable-frequency motor (1), a brake (3), a controller (4), a drum (6), a speed reducer (7), a steel wire rope (8), a pulley (9), a tensioning trolley (10), a belt (11), a buffer oil cylinder (12) and a hydraulic system. The belt (11) is wound around the redirecting roller of the tensioning trolley (10), and the pulley (9) is connected to the other side of the tensioning trolley (10). It is characterized in that, One end of the brake (3) is connected to the power output end of the frequency conversion motor (1) through the coupling Ⅰ (2), and the other end is connected to the input shaft of the speed reducer (7) through the coupling Ⅱ (5). The output shaft of the speed reducer (7) is connected to the drum (6). One end of the steel wire rope (8) is fixedly connected to the drum (6) and wound around the drum (6), and the other end passes around the pulley (9) and is connected to the movable end of the buffer oil cylinder (12). The buffer oil cylinder (12) is connected to the brake (3) through a hydraulic system. The brake (3) and the controller (4) are connected through multiple groups of oil pipes.

2. The variable-frequency tensioning device for a belt conveyor according to claim 1, wherein, The brake (3) includes a brake housing (3-3). A brake shaft (3-1) is provided on the brake housing (3-3). Both ends of the brake shaft (3-1) extend out of the brake housing (3-3) and are respectively connected to the frequency conversion motor (1) and the speed reducer (7) through the coupling Ⅰ (2) and the coupling Ⅱ (5). A brake piston (3-4) slidably sleeved on the brake shaft (3-1) is arranged inside the brake housing (3-3). One end of the brake piston (3-4) is connected with a brake spring (3-2) sleeved on the brake shaft (3-1), and the other end of the brake spring (3-2) is connected to the end plate of the brake housing (3-3). A static friction plate (3-6) is connected to one end of the brake housing (3-3) far from the brake spring (3-2). A dynamic friction plate (3-5) matching with the static friction plate (3-6) is provided on the brake shaft (3-1). A brake oil port Ⅰ (3-A) is provided at one end of the brake housing (3-3) close to the brake spring (3-2), a brake oil port Ⅱ (3-B) is provided at one end close to the static friction plate (3-6), and a brake oil port Ⅲ (3-C) connecting the hydraulic system is provided between the brake piston (3-4) and the static friction plate (3-6).

3. The variable-frequency tensioning device for a belt conveyor according to claim 2, characterized in that, The controller (4) includes a controller housing (4-1). A controller piston (4-2) and a tapered valve core (4-3) are connected inside the controller housing (4-1). A large spring (4-4) is connected to the large end face of the tapered valve core (4-3), and the other end of the large spring (4-4) is connected to the end face of the controller housing (4-1). A control valve core (4-6) is sleeved inside the tapered valve core (4-3). The control valve core (4-6) forms a movable connection with the end face shaft hole of the controller piston (4-2). A small spring (4-5) is connected to the end face of the control valve core (4-6). The small spring (4-5) is sleeved inside the large spring (4-4), and the other end is connected to the end face of the controller housing (4-1). A controller oil port Ⅰ (4-A) is provided on the end face of the controller housing (4-1) close to the controller piston (4-2). A controller oil port Ⅱ (4-B) is provided between the controller piston (4-2) and the tapered valve core (4-3). A controller oil port Ⅲ (4-C) is provided on the end face connected with the large spring (4-4).

4. The variable-frequency tensioning device for a belt conveyor according to claim 3, characterized in that, The brake oil port Ⅰ is communicated with the controller oil port Ⅱ (4-B) through an oil pipe. The brake oil port Ⅱ (3-B) is communicated with the controller oil port Ⅰ (4-A) and the controller oil port Ⅲ (4-C) through an oil pipe.

5. The variable-frequency tensioning device for a belt conveyor according to any one of claims 1-4, characterized in that, The buffer oil cylinder (12) includes a cylinder barrel (12-1). An oil cylinder piston (12-2) is arranged inside the cylinder barrel (12-1). A piston rod (12-4) is connected to the oil cylinder piston (12-2). The other end of the piston rod (12-4) extends out of the cylinder barrel (12-1) and is connected to a steel wire rope (8). A displacement sensor (12-3) is connected to the piston rod (12-4). The other end of the displacement sensor (12-3) passes through the oil cylinder piston (12-2) and extends out of one end of the cylinder barrel (12-1). An oil cylinder oil port (12-A) for connecting a hydraulic system is arranged at one end of the cylinder barrel (12-1) close to the piston rod (12-4).

6. The variable-frequency tensioning device for belt conveyors according to claim 5, characterized in that, The hydraulic system includes a gear pump (17) and a pump station motor (18) fixedly connected thereto. The outlet of the gear pump (17) is connected to an electromagnetic reversing valve I (19). Meanwhile, a relief valve II (16) is connected in parallel at the outlet of the gear pump (17). The oil outlet of the electromagnetic reversing valve I (19) is divided into two paths and is respectively connected to a check valve I (15) and a check valve II (22). The outlet of the check valve I (15) is connected to the oil cylinder oil port (12-A). Meanwhile, a pressure transmitter I (13) and a relief valve I (14) are connected in parallel at the outlet of the check valve I (15). The outlet of the check valve II (22) is connected to a brake oil port III (3-C). Meanwhile, a pressure transmitter II (23) and an electromagnetic reversing valve II (20) are connected in parallel at the outlet of the check valve II (22). The oil outlets of the relief valve I (14), the relief valve II (16), the oil suction port of the gear pump (17), the oil outlet of the electromagnetic reversing valve II (20) and the oil return port are all connected to an oil tank (21).

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