GB2315102A

GB2315102A - Hydraulic system for power loaders

Info

Publication number: GB2315102A
Application number: GB9714578A
Authority: GB
Inventors: Li Anatoli Deninovich
Original assignee: Samsung Heavy Industries Co Ltd
Current assignee: Samsung Heavy Industries Co Ltd
Priority date: 1996-07-10
Filing date: 1997-07-10
Publication date: 1998-01-21
Also published as: DE19729167A1; KR100205568B1; CN1170831A; JPH1082368A; KR980009964A; GB9714578D0

Abstract

A hydraulic system for power loaders, selectively changing the amount of pump discharged oil in accordance with an operational condition of a loader and improving operational efficiency of the loader, is disclosed. The system has a swash plate-type main pump 1 for discharging pressurized oil for working and steering parts of the system, a swash plate-type pilot pump 2 for discharging pressurized oil for a pilot signal output control lever 5, and a regulator 9. The regulator 9 is mounted to a first branch oil passage 9A branched from a main oil passage 1A extending from each of the main and pilot pumps 1,2. The regulator 9 selectively controls the angle of the swash plate of each of the main and pilot pumps 1,2 in accordance with a variable pressure of the first branch passage 9A.

Description

2315102 HYDRAULIC SYSTEM FOR POWER LOADERS

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a hydraulic system for construction equipment and, more particularly, to a hydraulic system for power loaders, having main and pilot pumps with variable swash plates thus selectively changing the amount of pump discharged oil in accordance with an operational condition of a loader and improving operational efficiency of the loader.

2. Description of the Prior Art

As well known to those skilled in the art, a power loader is a type of construction equipment used for bucketing and loading bulk materials such as sand or pebbles onto, for example, a dump truck. Such a loader is operated by a hydraulic system with main and steering pumps. The main and steering pumps are operated by an engine output power and respectively discharge pressurized oil for working cylinders, such as lift and dump cylinders associated with boom and bucket, and pressurized oil for a steering cylinder.

Fig. 2 shows the construction of a typical hydraulic system for power loaders. In the drawing, the main and steering pumps of the system are represented by the reference numerals 2 and 3. respectively. The system also includes a plurality of steering and working cylinders 10, 17 and 18. An example of working cylinders 17 and 18 is a lift cylinder, a dump cylinder, etc. The working cylinders 17 and 18 are operated by discharged oil of the main pump 2 thus actuating the working units such as a boom and a bucket. Meanwhile, the steering cylinder 10 is operated by discharged oil of the steering pump 3 thus steering the power loader. In order to control the flowing direction of pressurized oil for the working cylinders 17 and 18, two directional control valves 14 and 16 are mounted to the working oil passage extending from the main pump 2 to the working cylinders 18 and 17. A steering spool 6 is mounted to the steering oil passage extending from the steering pump 3 to the steering cylinder 10 and is operated in accordance with a signal indicative of an operator's handling motion of a steering wheel (not shown). The system further includes a demand spool 5. This spool 5 controls the amount of pressurized oil for both the working oil passage and the steering oil passage in response to a pilot signal of the steering oil passage.

In Fig. 2, the reference numeral 1 denotes an oil tank, 4 denotes a check valve which is mounted to the interconnection passage connecting the working and steering oil passages together, 7 denotes a relief valve for the steering oil passage, 11 denotes a relief valve for the working oil passage, 8 denotes a suction valve for the steering oil passage, and 12 denotes a suction valve for the working oil passage.

When the internal combustion engine of a loader is.s.tarted,. pressurized oil is discharged from the main pump 2 to the control 2 valves 14 and 16 through the passage 2A. The valves 14 and 16 control the flowing direction of the oil prior to feeding the oil to the working cylinders 17 and 18. Meanwhile, the steering pump 3 discharges pressurized oil to the steering spool 6 so that the spool 6 controls the flowing direction of the oil prior to feeding the oil to the steering cylinder 10.

When the loader is in a neutral mode or a loadless mode, the pump discharged oil does not pass through either the working or steering oil passage, thus stopping the cylinders 10, 17 and 18. In such a neutral mode, the spool of each of the control valves is positioned at its neutral position so that the discharged oil from the two pumps 2 and 3 returns to the oil tank 1 by way of the control valves. In the typical hydraulic system for power loaders. a fixed pump, which has a fixed swash plate causing the pump to discharge a fixed amount of oil regardless of operational modes, is used as each of the pumps 2 and 3. The pumps 2 and 3 with fixed swash plates thus discharge a fixed amount of oil even on a neutral mode thus wasting engine or pump output power. Such pumps 2 and 3 also cause a fixed amount of oil to pass through each of the control valves, thus reducing the durability of each valve and reducing the expected life span of the system.

SUMALLRY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art. An object of the present invention is to provide a hydraulic system for power loaders, which selectively reduces the amount of pump discharged oil in the event of a neutral mode of a loader, thus saving the engine output power and improving the operational efficiency of the loader.

Another object of the present invention is to provide a hydraulic system for power loaders, which effectively maintains a constant pressure inside the oil passage even on a neutral mode of a loader, thus improving the response performance of the loader.

A further object of the present invention is to provide a hydraulic system for power loaders, which allows the pump discharged oil to pass through a bypass line in the event of a neutral mode of a loader, thus allowing the main pump to be operated without being loaded, saving the pump output power, preventing unexpected overheating of the pump, lengthening the expected life span of the pump, preventing the increase of oil temperature and being free from a reduction of operational performance or unexpected damage of the actuators.

In an aspect, the present invention provides a hydraulic system for power loaders, comprising a swash plate-type main pump for discharging pressurized oil for working and steering parts of the system, and a swash plate-type pilot pump for discharging pressurized oil for a control lever, the control lever outputting a pilot signal for a control valve of the working part, further comprising a regulator mounted to a first branch oil passage branched from a main oil passage extending from each of the main and pilot pumps, the regulator being adapted for selectively controlling the angle of the swash plate of each of the main and pilot pumps in accordance with a variable pressure of the first branch passage.

The regulator comprises: a servo cylinder having: a piston movably received in the servo cylinder thus dividing the interior of the servo cylinder into small and large chambers, the piston being connected to the swash plate of each of the main and pilot pumps: and biasing means installed in the large chamber of the servo cylinder and normally biasing the piston toward the small chamber: a second branch passage branched from the first branch passage to the small chamber of the servo cylinder: a third branch passage branched from the first branch passage to the large chamber of the servo cylinder; an interconnection passage extending from the first branch passage and connecting the second and third branch passages together; an orifice mounted to the interconnection passage and adapted for selectively checking the amount of oil for the third branch passage; and a proportional valve mounted to an oil passage extending from the third branch passage to a drain passage, the proportional valve being biased by a biasing member and selectively allowing the oil of the third branch passage to be drained through the drain passage in accordance with the difference between the biasing pressure of the biasing member and the oil pressure inside the second branch passage.

The biasing pressure of the biasing member is adjustable by a user.

The hydraulic system further comprises: an accumulator mounted to the main oil passage and adapted for accumulating surplus discharged oil of each of the main and pilot pumps; and a check valve mounted to the main oil passage at a position between each of the main and pilot pumps and the accumulator and adapted for preventing unexpected reverse flow of the accumulated oil from the accumulator into each of the pumps.

The hydraulic system further comprises: a passage control valve mounted to a fourth branch passage branched from the main oil passage to a drain passage, the passage control valve being adapted for normally closing the fourth branch passage and selectively opening the fourth branch passage in response to a predetermined signal.

In another aspect, the present invention provides a hydraulic system for power loaders, comprising a swash plate-type main pump for discharging pressurized oil for working and steering parts of the system, and a swash plate-type pilot pump for discharging pressurized oil for a control lever, the control lever outputting a pilot signal for a control valve of the working part, further comprising: a regulator mounted to a first branch oil passage branched from a main oil passage extending from each of the main and pilot pumps, the regulator being adapted for selectively controlling the angle of the swash plate of each of the main and pilot pumps in accordance with a variable pressure of the first branch passage; an accumulator mounted to the main oil passage and adapted for accumulating surplus discharged oil of each of the main and pilot pumps; a check valve mounted to the main oil passage at a position between each of the main and pilot pumps and the accumulator and adapted for preventing unexpected reverse flow of the accumulated oil from the accumulator into each of the pumps; and a passage control valve mounted to a fourth branch passage branched from the main oil passage to a drain passage, the passage control valve being adapted for normally closing the fourth branch passage and selectively opening the fourth branch passage in response to a predetermined signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. la is a view showing the construction of a hydraulic system for power loaders in accordance with the preferred embodiment of. the present invention; Fig. lb is a view showing in detail the main pump with an improved regulator according to this invention; and Fig. 2 shows the construction of a typical hydraulic system for power loaders.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figs. la and lb show the construction of a hydraulic system for power loaders in accordance with the preferred embodiment of the present invention. As shown in the drawings, the hydraulic system of this invention includes a working part and a travelling part, which are operated by pressurized oil discharged from a main pump 1 through a main passage or a lst passage 1A. The travelling part, which controls the travelling condition of a power loader, comprises a steering unit 3 and two steering cylinders 11 and 12. The steering unit 3 controls the pressurized oil of the Ist passage 1A in accordance with a steering signal indicative of an operator's handling motion of a steering wheel (not shown). The steering cylinders 11 and 12 are actuated by the pressurized oil under the control of the steering unit 3, thus steering the loader. The travelling part also includes a cushion means 13 which relieves an impact unexpectedly applied to the system while the loader is steered.

Meanwhile, the working part, which controls the working units of the loader such as a boom or a bucket, includes a main control unit 4, which controls the pressurized oil flowing through the Ist passage IA in response to a pilot signal a, b, c, d, f. g or h. Two cylinders or dump and lift cylinders 1-6 and 17 are connected to the main control unit 4 and operate the working units or the bucket and boom, respectively. The working part also includes a relief valve 15 which limits the oil pressure of the hydraulic system to a predetermined level thus protecting the hydraulic system from unexpected overpressure.

The hydraulic system also includes a control lever unit 5, which is mounted to a 2nd passage 2A extending from a pilot pump 2. The lever unit 5 outputs a pilot signal in response to an operator's handling motion. The pressurized oil for the lever unit 5 is controlled by a pilot signal output unit 19.

In Figs. la and lb, the reference numeral 18 denotes an emergency steering unit, 20 denotes a cooler for cooling the return oil, 21 denotes an oil tank, and 22 denotes an air breather.

The hydraulic system also has a regulator 9, an accumulator 7 and a check valve 6. The regulator 9 is connected to the lst passage 1A through a 1st branch passage 9A so that it receives feedback pressure from the 1st passage 1A and changes the angle of the swash plate of the main pump 1, thus changing the amount of discharged oil of the pump 1. The accumulator 7 is mounted to the Ist passage 1A and accumulates surplus discharged oil of the pump 1, thus maintaining a desirable oil pressure of the 1st passage IA for both the working and travelling parts. The check valve 6 prevents unexpected reverse flow of the accumulated oil from the accumulator 7 into the pump 1.

While the loader is in a working mode or a travelling mode, the regulator 9 increases the angle of the swash plate of the main pump 1 in response to the feedback pressure from the Ist passage IA, thus increasing the amount of discharged oil of the pump 1 to the maximum level. On the contrary, the regulator 9 during a neutral mode reduces the angle of the swash plate of the pump 1, thus reducing the amount of discharged oil of the pump 1 to the minimum level. In order to achieve the above-described operation, the regulator 9 has a servo cylinder 90, an orifice 96 and a proportional valve 97, with 2nd and 3rd branch passages 90A and 90B being branched from the Ist branch passage 9A. The servo cylinder 90 has two chambers: small and large chambers 91 and 92 which communicate with the 2nd and 3rd branch passages 90A and 90B respectively. The orifice 96 is' mounted to an interconnection passage 90C, which extends from the lst branch passage 9A while connecting the 2nd and 3rd branch passages 90A and 90B together. The proportional valve 97 is biased by a 2nd biasing member 98 so that the valve 97 selectively allows the 3rd branch passage 90B to communicate with a drain passage 21A in accordance with the difference between the biasing pressure of the biasing member 98 and the oil pressure inside the 2nd branch passage 90A. A piston 93 is movably installed in the servo cylinder 90, with a piston rod 94 connecting the piston 93 to the swash plate of the main pump 1 thus selectively changing the angle of the swash plate in accordance with the linear movement of the piston 93 in the cylinder 90. The servo cylinder 90 also has a lst biasing member 95, which is installed in the large chamber 92 of the cylinder 90 and normally biases the piston 93 to the right in Fig. lb.

In the proportional valve 97, the biasing pressure of the 2nd biasing member 98 may be freely adjusted by a user.

A 4th branch passage 8A is branched from the Ist passage IA and extends to the drain passage 2 1A, with a passage control valve 8 being mounted to the 4th branch passage 8A. The passage control valve 8 with a valve spring normally closes the passage 8A and selectively opens the passage 8A when it receives a predetermined signal.

In order to control the amount of discharged oil of the pilot pump 2, a regulator 17 controls the angle of the swash plate of the pilot pump 2. The operation of the regulator 17 is the same as that described for the regulator 9 of the main pump 1 and further explanation is thus not deemed necessary.

The operational effect of the hydraulic system of this invention will be described hereinbelow.

When the hydraulic system is operated in a neutral mode or a loadless mode with the control valves of the system being positioned at their neutral positions, the discharged oil of the pump 1 increases the pressure of the passage 1A to a predetermined level at which the relief valve 15 is started. That is, when the passage control valve 8 closes the passage 8A with both the 3rd passage 3A for the steering unit and the 4th passage 4A for the working part being closed, the pressure of the passage 1A is increased to the relief valve start pressure because of the discharged oil of the pump 1. The accumulator 7 in the above state accumulates the pressurized oil, while the regulator 9 reduces the angle of the swash plate of the main pump 1 thus reducing the amount of discharged oil of the pump 1 to the minimum level. In detailed description. the pressure, which acts on one side of the piston

93 due to the pressurized oil applied into the small chamber 91 of the servo cylinder 90 through the Ist and 2nd branch passages 9A and 90A, is higher than the pressure, which acts on the other side of the piston 93 due to both the pressurized oil, supplied into the large chamber 92 through both the orifice 96 and the 3rd branch passage 90B, and the biasing pressure of the lst biasing member 95. Therefore, the piston 93 moves to the left in Fig. lb. In this case, the proportional valve 97 allows the 3rd branch passage 90B to communicate with the drain passage 21A because the pilot pressure caused by the oil pressure of the 2nd branch passage 90A is higher than the biasing pressure of the 2nd biasing member 98. The proportional valve 97 thus causes the pressurized oil of the large chamber 92 to be returned to the oil tank 21 through the drain passage 21A in proportion to the moving stroke of the piston 93 inside the cylinder 90. Both the moving stroke and the moving speed of the piston 93 may be changed by adjusting the biasing pressure of the biasing member 98.

When the passage control valve 8 is opened, the drain passage 21A communicates with the 4th branch passage 8A so that the discharged oil of the main pump I does not pass through either passage for the working and steering units but returns to the oil tank 21. Even on the above state, the lst passage 1A maintains a desirable oil pressure due to the accumulator 7.

When all of the working and steering parts of the system are started simultaneously, the pressurized oil of the accumulator 7 is primarily supplied, while the passage control valve 8 is closed, causing the discharged oil of the main pump 1 to be supplied to the working and steering parts. The angle of the swash plate of the main pump 1 in the above state is increased so that the amount of discharged oil of the pump 1 is increased. That is, as the pilot pressure acting on the proportional valve 97 due to the pressurized oil of the 2nd branch p assage 90A is reduced, the drain port of the proportional valve 97 gets closed and thus the pressure of the 3rd branch passage 90B gets' increased. The pressure inside the small chamber 91 in the above state is reduced, thus the piston 93 is moved to the right in Fig. lb by the Ist biasing member 95 whereby the angle of the swash plate of the pump 1 is increased.

As described above, the present invention provides a hydraulic system for power loaders, which selectively reduces the amount of pump discharged oil during a neutral mode of a loader. thus saving the engine output power and improving operational efficiency of the loader. The system also effectively maintains a constant pressure inside the oil passage even on the neutral mode. thus improving the response performance of the loader. In addition, the system allows the pump discharged oil to pass through a bypass line during a neutral mode thus allowing the main pump to be operated without being loaded and saving the pump output power. The system thus prevents unexpected overheating of the pump, lengthening the expected life span of the pump, and prevents the increase of oil temperature thus preventing both the reduction of operational performance and unexpected damage of the actuators.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

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Claims

WHAT IS CLAIMED IS:

1. A hydraulic system for power loaders, comprising a swash plate-type main pump for discharging pressurized oil for working and steering parts of the system, and a swash plate-type pilot pump for discharging pressurized oil for a control lever. said control lever outputting a pilot signal for a control valve of said working part, further comprising:

a regulator mounted to a first branch oil passage branched from a main oil passage extending from each of the main and pilot pumps, said regulator being adapted for selectively controlling the angle of the swash plate of each of said main and pilot pumps in accordance with a variable pressure of the first branch passage.

2. The hydraulic system according to claim 1, wherein said regulator comprises:

servo cylinder having:

piston movably received in said servo cylinder thus dividing the interior of said servo cylinder into small and large chambers, said piston being connected to the swash plate of each of the main and pilot pumps, and biasing means installed in the large chamber of the servo cylinder and normally biasing the piston toward the small chamber; a second branch passage branched from the first branch passage to the small chamber of the servo cylinder; a third branch passage branched from the first branch passage to the large chamber of the servo cylinder; an interconnection passage extending from the first branch passage and connecting the second and third branch passages together; an orifice mounted to said interconnection passage and adapted for selectively checking the amount of oil for the third branch passage; and a proportional valve mounted to an oil passage extending from the third branch passage to a drain passage, said proportional valve being biased by a biasing member and selectively allowing the oil of the third branch passage to be drained through the drain passage in accordance with the difference between the biasing pressure of the biasing member and the oil pressure inside the second branch passage.

3. The hydraulic system according to claim 2, wherein the biasing pressure of said biasing member is adjustable by a user.

4. The hydraulic system according to claim 1, further comprising:

a an accumulator mounted to said main oil passage and adapted for accumulating surplus discharged oil of each of the main and pilot pumps; and a check valve mounted to the main oil passage at a position between each of the main and pilot pumps and said accumulator and adapted for preventing unexpected reverse flow of the accumulated oil 17 - from the accumulator into each of the pumps.

5. The hydraulic system according to claim 1, further comprising: a passage control valve mounted to a fourth branch passage branched from the main oil passage to a drain passage, said passage control valve being adapted for normally closing the fourth branch passage and selectively opening the fourth branch passage in response to a predetermined signal.

6. A hydraulic system for power loaders, comprising a swash plate-type main pump for discharging pressurized oil for working and steering parts of the system, and a swash plate-type pilot pump for discharging pressurized oil for a control lever, said control lever outputting a pilot signal for a control valve of said working part, further comprising: a regulator mounted to a first branch oil passage branched from a main oil passage extending from each of the main and pilot pumps, said regulator being adapted for selectively controlling the angle of the swash plate of each of said main and pilot pumps in accordance with a variable pressure of the first branch passage; an accumulator mounted to said main oil passage and adapted for accumulating surplus discharged oil of each of the main and pilot pumps; a check valve mounted to the main oil passage at a position between each of the main and pilot pumps and said accumulator and 18 - adapted for preventing unexpected reverse flow of the accumulated oil from the accumulator into each of the pumps; and a passage control valve mounted to a fourth branch passage branched from the main oil passage to a drain passage, said passage control valve being adapted for normally closing the fourth branch passage and selectively opening the fourth branch passage in response to a predetermined signal.

7. The hydraulic system according to claim 6, wherein said regulator comprises:

servo cylinder having:

piston movably received in said servo cylinder thus dividing the interior of said servo cylinder into small and large chambers, said piston being connected to the swash plate of each of the main and pilot pumps; and biasing means installed in the large chamber of the servo cylinder and normally biasing the piston toward the small chamber; a second branch passage branched from the first branch passage to the small chamber of the servo cylinder; a third branch passage branched from the first branch passage to the large chamber of the servo cylinder; an interconnection passage extending from the first branch passage and connecting the second and third branch passages together; an orifice mounted to said interconnection passage and adapted for selectively checking the amount of oil for the third branch passage: and a proportional valve mounted to an oil passage extending from the third branch passage to a drain passage, said proportional valve being biased by a biasing member and selectively allowing the oil of the third branch passage to be drained through the drain passage in accordance with the difference between the biasing pressure of the biasing member and the oil pressure inside the second branch passage.

8. The hydraulic system according to claim 7, wherein the biasing pressure of said biasing member is adjustable by a user.