WO2008069552A1

WO2008069552A1 - Steering control system for construction equipment

Info

Publication number: WO2008069552A1
Application number: PCT/KR2007/006255
Authority: WO
Inventors: In-Pyo Jang; Soung-Kyun Lee
Original assignee: Doosan Infracore Co., Ltd.
Priority date: 2006-12-04
Filing date: 2007-12-04
Publication date: 2008-06-12
Also published as: KR101294406B1; KR20080050692A

Abstract

Disclosed is a steering control system for construction equipment, which controls the rotating speed of a steering wheel of the construction equipment. When the construction equipment is driven at a low speed, the steering control system substantially prevents a difference between a rotating speed of the steering wheel manipulated by a driver and a real steering speed of the construction equipment such as a wheel loader. Thereby, the accidents caused by the difference between the rotating speed of the steering wheel manipulated by the driver and the real steering speed of the construction equipment can be prevented.

Description

[DESCRIPTION]

[invention Title]

STEERING CONTROL SYSTEM FOR CONSTRUCTION EQUIPMENT [Technical Field] The present invention relates to a steering control system for construction equipment and, more particularly, to a steering control system for construction equipment, which, in the event of insufficient supply of hydraulic operating fluid, increases the force required to manipulate a steering wheel to thereby hinder smooth rotation of the steering wheel, thereby enabling a rotating speed of the steering wheel to correspond to a steering speed of the construction equipment such as a wheel loader.

[Background Art] In general, construction equipment refers to any vehicle, such as an excavator, a wheel loader or bulldozer, used for any designated work in a construction site, and has a body that is relatively heavier and bigger than other type of vehicles. In the cases of some construction equipments, such as a wheel loader that performs working together with traveling or running, steering characteristics required for the traveling are important, in addition to working characteristics. Unlike the ordinary vehicles, these kinds of construction equipment are typically designed to be steered using hydraulic pressure due to their heaviness of the body and a load of carried material such as earth and sand.

FIG. 1 illustrates a hydraulic steering system for a wheel loader as an example of conventional construction equipment .

The hydraulic steering system illustrated in FIG. 1 comprises a steering pump P, a steering cylinder 3, which selectively performs expansion and contraction by hydraulic operating fluid of the steering pump P, a steering valve unit

2, which is connected with a steering hydraulic pressure supply line 12 connected to the steering pump P and selectively connects the steering hydraulic pressure supply line 12 to steering hydraulic lines CL and CR connected to each of hydraulic chambers 3a and 3b of the steering cylinder 3 respectively, and a steering wheel pump (called an orbitrol pump) 100, which interacts with manipulation of a steering wheel 6 and switches a steering control valve (not shown) installed on the steering valve unit 2. The steering wheel pump 100 typically makes use of the orbitrol pump, as illustrated in the figure, for the construction equipment. Thus, hereinafter, the steering wheel pump 100 is referred to as the "orbitrol pump."

Meanwhile, the steering hydraulic pressure supply line 12 is provided with a priority valve (not shown) . This priority valve supplies all the hydraulic operating fluid of the steering pump P to the steering valve unit 2 when steering is performed without working (hereinafter, referred to as "independent steering") , but supplies most of the hydraulic operating fluid of the steering pump P to a cylinder (not shown) for working and only the remaining small quantity to the steering valve unit 2 when steering is not performed.

In the hydraulic steering system for the wheel loader, when a steering control valve, not shown, is switched in one direction by manipulation of the steering wheel 6, the hydraulic operating fluid of the steering pump P is supplied to one of the hydraulic chambers 3a and 3b of the steering cylinder 3, and thus deflects the steering cylinder 3 in one direction. Thereby, the wheel loader is steered. Here, a steering pilot line SP branches off from a hydraulic line, which connects the steering control valve (not shown) and the priority valve (not shown) , and is connected to an inlet of the orbitrol pump 100.

The orbitrol pump 100 applies steering pilot pressure, which is provided through the steering pilot line SP depending on the manipulation of the steering wheel 6, to one of opposite ports of the steering control valve, thereby switching the steering control valve. In this manner, when the steering control valve is switched, hydraulic operating fluid is supplied from the orbitrol pump P to one of the hydraulic chambers 3a and 3b of the steering cylinder 3, thereby operating the steering cylinder 3 to enable the steering of the construction equipment (for example, a wheel loader) . However, this steering system for the wheel loader insufficiently supplies the hydraulic operating fluid to the steering cylinder from the orbitrol pump P in a low-speed engine state in which a supply flow rate of the orbitrol pump P is insufficient. This low-speed engine state means that a traveling speed of the wheel loader is slow. In this case, the operation of the steering cylinder is slow, so that wheels of the wheel loader are slowly steered. In the meantime, the flow rate required for the orbitrol pump is less than that required for the steering cylinder, so that the insufficient flow rate from the pump P does not mean that the flow rate supplied to the orbitrol pump is insufficient.

In detail, although the supply flow rate of the hydraulic operating fluid from the pump P is insufficient, the orbitrol pump interacting with the steering wheel 6 can be supplied with the hydraulic operating fluid enough to rotate the steering wheel, and thus the steering wheel 6 can be rotated rapidly enough; however, the flow rate supplied to the steering cylinder from the pump P is insufficient, so that the steering cylinder may be operated at a speed, which is slower than the desired level of a driver.

Thus, although the driver rotates the steering wheel 6 such an extent that he/she regards the steering of the wheel loader as sufficiently performed, the wheels of the wheel loader are actually steered insufficiently, so that a risk of an accident exists during traveling. That is, in the low-speed engine state of the wheel loader, the driver can have an illusion that the rapid manipulation of the steering wheel 6 can result in the rapid steering of the wheel loader itself, without recognizing insufficient steering of the wheel loader. As a result, the accident such as collision or turnover really takes place. [Disclosure] [Technical Problem]

Accordingly, the present invention has been made in an effort to solve the problems occurring in the above conventional art, and an object of the present invention is to provide a steering control system for construction equipment, which controls the rotating speed of a steering wheel so as to correspond to the real steering speed of the construction equipment such as a wheel loader while the construction equipment is traveling. [Technical Solution] In order to achieve the above object, according to one aspect of the present invention, there is provided a steering control system for construction equipment, which comprises: a steering control valve 7, which is connected with a pump P, with a tank T, and with a steering cylinder 3 for controlling steering of traveling wheels; an orbitrol pump 1, which interacts with a steering wheel 6 and provides a steering signal to the steering control valve 7; a steering pilot line 18, which branches off from a hydraulic line connecting the steering control valve 7 and the pump P and is connected with a hydraulic operating fluid inlet of the orbitrol pump 1 at one end thereof; and a flow restricting valve 5, which is connected to the steering pilot line 18 and is switched depending on a flow rate of hydraulic operating fluid supplied to the steering cylinder 3, wherein the flow restricting valve 5 restricts a flow rate, which is supplied to the orbitrol pump 1 via the steering pilot line 18, to increase handling force required to manipulate the steering wheel 6, when a flow rate of a hydraulic line CF (or 12) guiding the hydraulic operating fluid from the pump (P) to the steering cylinder 3 is equal to or less than a preset reference flow rate.

According to an example of the present invention, the flow restricting valve 5 may include an orifice, and be switched so as to cause the hydraulic operating fluid supplied to the orbitrol pump 1 to pass through the orifice when pressure of the hydraulic line CF is equal to or less than a preset reference pressure.

According to another example of the present invention, the steering control system for construction equipment may further comprise: a priority valve 4, which is interposed between the steering control valve 7 and the pump P and selectively supplies part of flow rate of the pump to other working unit; and a load sensing signal line LS, which connects one port of the priority valve 4 with the steering control valve 7 and switches the priority valve 4 in response to operation of the steering control valve 7, wherein the flow restricting valve 5 is switched so as to cause the hydraulic operating fluid supplied to the orbitrol pump 1 to pass through the orifice, when a pressure difference between the load sensing signal line LS and the hydraulic line CF is equal to or less than a preset value.

According to another example of the present invention, the steering control system for construction equipment may further comprise a sensor 15, which measures the pressure of the steering hydraulic pressure supply line 12 (i.e. hydraulic line CF) , wherein the flow restricting valve 5 is switched in response to the pressure of the steering hydraulic pressure supply line 12 which is detected by the sensor 15. [Advantageous Effects]

According to the steering control system for construction equipment of the present invention, which can control the rotating speed of the steering wheel of the construction equipment, when the construction equipment is driven at a low speed, the steering control system substantially prevents a difference between a rotating speed of the steering wheel manipulated by a driver and a real steering speed of the construction equipment such as a wheel loader, so that it can prevent the accidents such as collision or turnover while the construction equipment is traveling, particularly on a curve.

[Description of Drawings]

FIG. 1 shows an example of a schematic hydraulic circuit illustrating the structure of a hydraulic steering system for conventional construction equipment, particularly a conventional wheel loader, as an example;

FIG. 2 shows an example of a schematic hydraulic circuit illustrating a steering control system for construction equipment, which can control the rotating speed of a steering wheel, according to the present invention taking a steering control system for a wheel loader as an example.

FIG. 3 shows an example of a schematic hydraulic circuit illustrating a steering control system, which can be applied to a wheel loader as an example of a construction equipment according to the present invention;

FIG. 4 is a conceptual view i Llustrating an orbitrol pump 1, which is applied to a steering control system according to an example of the present invention, wherein the orbitrol pump is provided with the Gerotor pump 13, and thus this orbitrol pump may be somewhat different from a real one, and the right- hand part of FIG. 4 is provided in order to describe a cross section of the Gerotor pump; and FIG. 5 is a schematic hydraulic circuit according to an example of the present invention illustrating a steering control system having a sensor 15 detecting hydraulic pressure.

<Description of Reference Numbers in the Drawings> P: pump (steering pump) V: control valve

1: steering wheel pump (orbitrol pump) 2: steering valve unit 3: steering cylinder 4 : priority valve

5: flow restricting valve 6: steering wheel 7: steering control valve 8, 9: pilot pressure valve 10: control unit (controller) 11: branch line

12: steering hydraulic pressure supply line 13: Gerotor pump 14: drain line 15: sensor

18: steering pilot line 20: steering wheel shaft 100: steering wheel pump [Mode for Invention] Hereinafter, the present invention will be described in detail by describing exemplary embodiments of the invention with reference to the attached drawings.

With respect to reference numerals, the same reference numerals are used for elements of the present invention which correspond to those of the prior art.

The following description will be made to a steering control system for construction equipment on the basis of a wheel loader having a traveling function. FIGS. 2 and 3 schematically illustrate a steering control system for construction equipment according to the present invention taking a steering control system for a wheel loader as an example . Referring to FIG. 2, the steering control system for construction equipment according to an example of the present invention comprises a steering valve unit 2, which is connected with a pump P and a tank T and is connected with a steering cylinder 3; an orbitrol pump 1, which interacts with a steering wheel 6; and a flow restricting valve 5, which is interposed between the steering valve unit 2 and a hydraulic operating fluid inlet of the orbitrol pump 1, restricting a flow rate supplied to the orbitrol pump 1 when an engine is in a low- speed state so as to increases manipulating force required for rotation of the steering wheel 6 and thus to restrict a rotating speed of the steering wheel 6 forcibly. The steering valve unit 2 can include one based on a pilot control system.

Here, the flow restricting valve 5 can be switched depending on a flow rate of hydraulic operating fluid supplied from the pump P to the steering cylinder 3.

In one exemplary embodiment of the present invention, hydraulic pressure of the hydraulic operating fluid supplied to the steering cylinder 3 may be measured instead of flow rate of the hydraulic operating fluid, and thereby the flow restricting valve 5 is switched depending on the measured hydraulic pressure. To this end, the flow restricting valve 5 is installed on a hydraulic line 18 between the steering valve unit 2 and the hydraulic operating fluid inlet of the orbitrol pump 1. Further, referring to FIG. 3, the steering control system for construction equipment, a wheel loader, according to the present invention comprises a steering control valve 7, which is connected with a pump P and a tank T and is connected with a steering cylinder 3 that controls steering of driving wheels; an orbitrol pump 1, which interacts with a steering wheel 6 and provides a steering signal to the steering control valve 7; a steering pilot line 18, which branches off from a hydraulic line connecting the steering control valve 7 and the pump P and is connected with the hydraulic operating fluid inlet of the orbitrol pump 1 at a terminal end thereof; and a flow restricting valve 5, which is switched depending on a flow rate of hydraulic operating fluid supplied from the pump P to the steering cylinder 3 from the pump P. When hydraulic pressure of a hydraulic line CF guiding the hydraulic operating fluid supplied from the pump P to the steering cylinder 3 is less than preset reference pressure, the flow restricting valve 5 restricts the flow rate supplied to the orbitrol pump 1 via the steering pilot line 18, and thereby increases manipulating force required to manipulate the steering wheel 6. As a result, the steering wheel is not easily rotated, so that the flow restricting valve 5 can control a rotating speed of the steering wheel 6. Further, when the hydraulic pressure of the hydraulic operating fluid supplied from the pump P to the steering cylinder 3 is equal to or less than the reference pressure, the flow restricting valve 5 restricts the flow rate supplied to the orbitrol pump 1, so that it can forcibly control the rotating speed of the steering wheel 6.

According to an example of the present invention, the flow restricting valve 5 is installed on the steering pilot line 18, which branches off from a steering hydraulic pressure supply line 12, which connects a priority valve 4 (see FIG. 3) , described below, and the steering control valve 7, and is connected with the orbitrol pump 1.

There is no particular limitation to the reference pressure, which is used as the criterion for the operation of the flow restricting valve 5. Thus, the reference pressure can be varied according to standards, use, etc. of the wheel loader. A person skilled in the art can individually set appropriate reference pressure for each construction equipment. According to an example of the present invention, in the wheel loader for ordinary working, the reference pressure can be set to 4 bar.

According to an example of the present invention, the flow restricting valve 5 includes an orifice valve. In this case, the flow restricting valve 5 can set a valve position where the flow is restricted to a basic valve position. Consequently, the flow restricting valve 5 includes an orifice, and can be adapted to be switched such that the hydraulic operating fluid supplied to the orbitrol pump 1 passes through the orifice when the hydraulic pressure of the steering hydraulic pressure supply line 12 is equal to or less than the reference pressure.

Meanwhile, according to an example of the present invention, the steering control system further comprises a priority valve 4, which is interposed between the steering control valve 7 and the pump P and selectively supplies part of the flow rate of the pump to other working unit(s), and a load sensing signal line LS, which switches the priority valve 4 using the pressure of the steering hydraulic pressure supply line 12 connected with the priority valve 4. Here, each of the opposite ports of the flow restricting valve 5 is connected with the load sensing signal line LS and the steering hydraulic pressure supply line 12 respectively, and thus pressure difference between the load sensing signal line LS and the steering hydraulic pressure supply 1 Lne 12 is equal to or less than a preset value, the flow restricting valve 5 can be adapted to be switched such that the hydraulic operating fluid supplied to the orbitrol pump 1 is restricted by the orifice.

The priority valve 4 functions to selectively pass the hydraulic operating fluid supplied from the pump. According to an example of the present invention, as the priority valve 4, a valve that sets a valve position where the pump P is connected with the steering control valve 7 to the basic valve position, and can be switched by pressure of the load sensing signal line LS of the steering hydraulic pressure supply line 12 may be used. Here, at a valve position where the priority valve 4 is connected with the steering control valve 7, the hydraulic operating fluid supplied from the pump P is supplied to the steering control valve 7 through the steering hydraulic pressure supply line 12 via the priority valve 4, and then, the hydraulic operating fluid is suppLied to a position that is corresponding to a switched state of the steering control valve 7. In the state in which the priority valve 4 is switched to the other valve position, the hydraulic operating fluid of the pump P can be adapted to be supplied to other working unit through a hydraulic line EF.

In this case, the flow restricting valve 5 can be disposed on the steering pilot line 18, which is connected between the steering hydraulic pressure supply line 12, which is disposed between the priority valve 4 and the steering control valve 7, and the hydraulic operating fluid inlet of the orbitrol pump 1, and is switched by the pressure of the steering hydraulic pressure supply line 12, through which the priority valve 4 is connected with the steering control valve 7.

When the pressure of the steering hydraulic pressure supply line 12, which connects the priority valve 4 with the steering control valve 7, is equal to or less than the reference pressure, the flow restricting valve 5 restricts such connection. In contrast, when the pressure of the steering hydraulic pressure supply line 12 exceeds the reference pressure, the flow restricting valve 5 does not restrict such connection. As an example of the flow restricting valve 5, there is an orfice valve. Of course, there is no particular limitation on the reference pressure. According to an example of the present invention, the reference pressure can be set to 4 bar. For example, when the hydraulic line, through which the pump P, the priority valve 4 and the steering control valve 7 are connected with each other, has pressure equal to and less than the reference pressure of 4 bar, the flow restricting valve 5 restricts the flow rate.

This flow restricting valve 5 is adapted to be operated in response to the flow rate supplied to the steering cylinder 3. In the case of the above-mentioned example, the flow restricting valve 5 responds to the hydraulic pressure of the steering hydraulic pressure supply line 12. In other words, the load sensing signal line LS of the priority valve 4 and the steering hydraulic pressure supply line 12 are connected to the opposite ports of the flow restricting valve 5 respectively, and thus the flow restricting valve 5 is operated by the pressure difference between the load sensing signal line LS and the steering hydraulic pressure supply line 12. Hence, in the case in which the differential pressure between the load sensing signal line LS and the steering hydraulic pressure supply line 12 is equal to or less than a preset pressure because the flow rate is sufficiently supplied to the steering cylinder 3, the flow restricting valve 5 is switched such that the flow rate of the steering pilot line 18 is restricted. In the opposite case, this restriction is released.

Meanwhile, the embodiment has been described that the flow restricting valve 5 is connected with the hydraulic lines 12 and LS and is switched using the pressure difference between the hydraulic lines 12 and LS. However, the present invention is not necessarily limited only to this embodiment.

According to another example of the present invention, as illustrated in FIG. 5, a separate sensor 15 is installed so as to measure the flow rate of the steering hydraulic pressure supply line 12, and the flow restricting valve 5 can be switched either by directly receiving a signal output from the sensor 15 or by indirectly receiving a signal output from the sensor 15 by way of a controller C that is a control unit 10. As described above, in the latter case, the flow restricting valve 5 can be more precisely controlled in consideration of other conditions such as the RPM of an engine and the traveling speed of a vehicle. For example, when the traveling speed exceeds a predetermined value, a flow rate of the steering pilot line 18 is controlled through the flow restricting valve 5, and thereby force required to manipulate the steering wheel is increased. As a result, both a low-speed steering safety and a high-speed steering safety can be improved.

Meanwhile, the steering control valve 7 is switched by the orbitrol pump 1 interacting with the steering wheel 6. According to an example of the present invention, the steering control valve 7 has a base valve position of neutral and is switched in response to an "L" or "R" signal of the orbitrol pump. The switched valve positions responding to the "L" or "R" signal of the orbitrol pump are referred to as first and second valve positions. For example, the first valve position of the steering control valve 7 allows the hydraulic operating fluid to be supplied to the steering cylinder 3, and permits the traveling wheels (not shown) to be turned to the left. In contrast, the second valve position allows the traveling wheels to be turned to the right. Meanwhile, when the steering control valve 7 is located at the neutral valve position, the hydraulic operating fluid is drained to the tank via a second pilot pressure valve 9, which will be described below.

According to another example of the present invention, the steering control system of the present invention further comprises a first pilot pressure valve 8, which is switched so as to block the steering pilot line 18 when pressure of the steering pilot line 18 exceeds a reference value. The flow restricting valve 5 is interposed between the first pilot pressure valve 8 and the hydraulic operating fluid inlet of the orbitrol pump 1.

In detail, referring to FIG. 3, the steering valve unit 2 further comprises a first pilot pressure valve 8 which is positioned on the steering pilot line 18 interposed between the steering hydraulic pressure supply line 12 and the orbitrol pump 1, and regulates the pressure of the steering hydraulic pressure supply line 12 to be equal to or less than a preset pressure. In this case, the flow restricting valve 5 can be interposed between the first pilot pressure valve 8 and the hydraulic operating fluid inlet of the orbitrol pump 1. According to an example of the present invention, the first pilot pressure valve 8 can be adapted to connect the hydraulic line at a basic valve position and to block the connection of the hydraulic line when the pressure exceeds a reference value. For example, the first pilot pressure valve 8 can function to connection the hydraulic line when the pressure of the steering pilot line 18 is equal to or less than a predetermined pressure, and to block the connection of the hydraulic line when the pressure of the steering pilot line 18 exceeds a predetermined pressure.

According to another example of the present invention, the steering control system of the present invention further comprises a branch line 11, which causes the hydraulic line between the steering control valve 7 and the tank T to connect with the hydraulic line between the first pilot pressure valve 8 and the orbitrol pump 1; and a second pilot pressure valve 9, which is interposed between the steering control valve 7 and the tank T and is switched by pressure of the branch line 11. As described above, the second pilot pressure valve 9 is interposed between the steering control valve 7 and the tank T.

Thus, when the steering control valve 7 is located at the neutral valve position, the hydraulic operating fluid is drained to the tank T via the second pilot pressure valve 9.

According to an example of the present invention, the second pilot pressure valve 9 blocks the connection of the hydraulic line at a basic valve position, and checks the pressure of the branch line 11, which branches off from the hydraulic line between the steering control valve 7 and the tank T and then is connected with the hydraulic line between the first pilot pressure valve 8 and the orbitrol pump 1. When the pressure of the branch line 11 exceeds a reference value, the second pilot pressure valve 9 is switched so as to permit the connection of the hydraulic line. Preferably, the reference pressure at which the second pilot pressure valve 9 is switched, is lower than that, at which the first pilot pressure valve 8 is switched. To this end, a check valve is installed on the branch line 11. According to an example of the present invention, the orbitrol pump 1 comprises a Gerotor pump 13, and a control valve V, which is switched such that hydraulic operating fluid, which is introduced through the steering pilot line 18 and then is pumped from the Gerotor pump 13, is guided to one of the opposite ports of the steering control valve 7. A rotational shaft 20 of the steering wheel 6 is connected to the Gerotor pump, so that the steering wheel 6 interacts with the orbitrol pump 1. At this time, the flow restricting valve 5 can be interposed between the steering valve unit 2 and a hydraulic operating fluid inlet of the Gerotor pump 13.

In FIG. 4, the right-hand part indicates the Gerotor pump, which is shown in a sectional view. FIG. 4 is for conceptually showing the orbitrol pump, which is provided with the Gerotor pump. Thus, the orbitrol pump shown in FIG. 4 may be different from a real one. In other words, the right-hand part 13 of FIG. 4 is provided to help understanding of the Gerotor pump. Thus, in fact, the part corresponding to the reference numeral 13 in FIG. 4 can be said to be a rdght-hand sectional part of the orbitrol pump located at the center.

As can be seen from FIG. 4, only when sufficient flow rate is supplied to the orbitrol pump 1, the shaft 20 of the steering wheel which is connected to the orbitrol pump can be easily rotated, and the steering wheel is easily rotated by a driver.

This rotation of the steering wheel by the driver is merely relevant to the flow rate of the hydraulic operating fluid supplied to the orbitrol pump, but is irrelevant to the flow rate of the hydraulic operating fluid supplied to the steering cylinder 3 of the wheel loader. Thus, even if the flow rate of the hydraulic operating fluid supplied to the steering cylinder 3 of the wheel loader is insufficient, the steering wheel 6 is easily operated as long as the flow rate of the hydraulic operating fluid supp] ied to the orbitrol pump is sufficient. As a result, even under the condition that the wheel loader itself is not sufficiently steered due to shortage of the hydraulic operating fluid supplied to the steering cylinder 3, there is a high probability of the driver believing that the steering wheel 6 grasped by himself/herself is sufficiently rotated, and thus believing that the wheel loader is also sufficiently turned.

For this reason, in the present invention, the flow restricting valve 5 as described above is installed to restrict the flow rate supplied to the orbitrol pump so as to correspond to the flow rate supplied to the steering cylinder of the wheel loader.

Here, the case in which the flow rate is restricted by the flow restricting valve 5 corresponds to the state in which the engine is operated at a low speed, i.e. the case in which the hydraulic operating fluid is not smoothly supplied from the pump P. In this case, even if the driver attempts to rotate the steering wheel 6 with excessive force, the flow rate supplied to the orbitrol pump 1 is restricted, and thus the steering wheel is not smoothly rotated. Thus, the steering speed can be synchronized with the rotating speed of the steering wheel 6. Now, the steering of the wheel loader will be described as follows.

Here, it is assumed that the priority valve 4 is located at a valve position at which the pump P is connected with the steering control valve 7, i.e. a basic valve position. The steering control system of the present invention steers the wheel loader in a manner such that, when the steering control valve 7 is switched to one valve position by the manipulation of the steering wheel 6, the hydraulic operating fluid of the steering pump P is subjected to direction control at the steering control valve 7, is then supplied to one of the hydraulic chambers 3a and 3b of the steering cylinder 3, and moves the steering wheel in one direction.

When the driver manipulates the steering wheel 6 to rotate the steering wheel 6 to the left or right, the signal L or R generated from the orbitrol pump 1 in response to the rotation is provided to the steering control valve 7. Thereby, the valve position of the steering control valve 7 is switched.

At this time, the flow restricting valve 5 maintains the state in which it is switched to a valve position at which the flow rate is not restricted.

In summary, the hydraulic operating fluid supplied from the pump P is supplied to the priority valve 4, the steering control valve 7 and the steering cylinder 3, so that the traveling wheels are turned to the left or right.

<When the flow rate supplied from the pump P is insufficient (or when the wheel loader engine is operated at a low speed> First, when the pressure of the hydraulic operating fluid of the hydraulic line, which connects the priority valve 4 with the steering control valve 7, is equal to or less than a reference value (4 bar) , the flow restricting valve 5 is switched to a basic valve position at which the flow rate is restricted.

Thus, the flow rate supplied to the orbitrol pump becomes insufficient, so that the driver has difficulty in manipulating the steering wheel 6. Thereby, the real steering speed of the wheel loader can mutually correspond to the rotating speed of the steering wheel 6 manipulated by the driver.

As a result, the accidents caused by the difference between the real steering speed of the wheel loader and the rotating speed of the steering wheel 6 manipulated by the driver can be prevented in advance. Although the exemplary embodiments of the present invention have been described, it is understood that the present invention should not be limited to these exemplary embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.

Claims

[CLAIMS]

[Claim l]

A steering control system for construction equipment comprising: a steering control valve (7), which is connected with a pump (P), with a tank (T), and with a steering cylinder (3) for controlling steering of traveling wheels; an orbitrol pump (1) , which interacts with a steering wheel (6) and provides a steering signal to the steering control valve (7); a steering pilot line (18), which branches off from a hydraulic line connecting the steering control valve (7) and the pump (P) and is connected with a hydraulic operating fluid inlet of the orbitrol pump (1) at one end thereof; and a flow restricting valve (5), which is connected to the steering pilot line (18) and is switched depending on a flow rate of hydraulic operating fluid supplied to the steering cylinder (3) , wherein the flow restricting valve (5) restricts a flow rate, which is supplied to the orbitrol pump (1) via the steering pilot line (18), to increase handling force required to manipulate the steering wheel (6) , when a flow rate of a steering hydraulic pressure supply line (12) guiding the hydraulic operating fluid from the pump (P) to the steering cylinder (3) is equal to or less than a preset reference flow rate.

[Claim 2]

The steering control system according to claim 1, wherein the flow restricting valve (5) includes an orifice, and is switched so as to cause the hydraulic operating fluid supplied to the orbitrol pump (1) to pass through the orifice when pressure of the steering hydraulic pressure supply line (12) is equal to or less than a preset reference pressure.

[Claim 3]

The steering control system according to claim 2, further comprising: a priority valve (4), which is disposed between the steering control valve (7) and the pump (P) and selectively supplies part of flow rate of the pump to other working unit; and a load sensing signal line (LS) , which switches the priority valve (4) using the pressure of the steering hydraulic pressure supply line (12) connected with the priority valve (4), wherein the flow restricting valve (5) is connected with the load sensing signal line (LS) and the steering hydraulic pressure supply line (12) at opposite ports thereof respectively, and is switched so as to cause the hydraulic operating fluid supplied to the orbitrol pump (1) to be restricted by the orifice, when a pressure difference between the load sensing signal line (LS) and the steering hydraulic pressure supply line (12) is equal to or less than a preset value .

[Claim 4]

The steering control system according to claim 2, further comprising a sensor (15) , which measures the pressure of the steering hydraulic pressure supply line (12) , wherein the flow restricting valve (5) is switched in response to the pressure of the steering hydraulic pressure supply line (12) which is detected by the sensor (15) .

[Claim 5] The steering control system according to any one of claims 1 through 4, further comprising a first pilot pressure valve (8) , which is switched so as to block the steering pilot line (18) when pressure of the steering pilot line (18) is more than a reference value, wherein the flow restricting valve (5) is interposed between the first pilot pressure valve (8) and the hydraulic operating inlet of the orbitrol pump (1) . [Claim 6]

The steering control system according to claim 5, wherein: the orbitrol pump (1) comprises a Gerotor pump (13) , which is operated in response to rotation of the steering wheel (6), and a control valve (V) , which is switched such that hydraulic operating fluid, which is pumped from the Gerotor pump (13) in response to the rotation of the steering wheel (6) , is guided to one of the opposite ports of the steering control valve (7); and the steering pilot line (18) is connected to a hydraulic operating inlet of the Gerotor pump (13) at one end thereof. [Claim 7]

The steering control system according to any one of claims 1 through 4, wherein: the orbitrol pump (1) comprises a Gerotor pump (13) , which is operated in response to rotation of the steering wheel (6); and a control valve (V) , which is switched such that hydraulic operating fluid, which is pumped from the Gerotor pump (13) in response to the rotation of the steering wheel (6), is guided to one of the opposite ports of the steering control valve (7); and the steering pilot line (18) is connected to a hydraulic operating inlet of the Gerotor pump (13) at one end thereof.