Patent Description:
<CIT> describes a hydraulic circuit for a construction machine. A hydraulic system for construction machinery may be divided into an open center type and a closed center type. In a hydraulic system of an excavator of the closed center type using a pressure control type electronic hydraulic pump, in case of a joystick sudden stop manipulation, a pressure peak occurs instantaneously by a working oil discharged from the hydraulic pump while a swash plate angle of the hydraulic pump is decreased. In order to reduce the pressure peak, a pump peak reducing valve (PPRV) may be used. However, an extra space and piping arrangement may be required and costs may be increased.

An object of the present invention provides a control system for construction machinery capable of reducing a pump peak at low cost.

Another object of the present invention provides a control method for construction machinery using the above control system.

The present invention provides a control system for construction machinery according to claim <NUM>.

In an embodiment, the controller may include a calculator determining an opening area of the bypass control valve based on a size and/or duration time of the pump peak that is expected to occur when the sudden stop manipulation occurs, and an output portion outputting a control signal for opening the first bypass control valve according to the determined opening area to prevent the pump peak when the sudden stop manipulation occurs.

In an embodiment, the calculator may determine an opening duration or a closing inclination of the first bypass control valve based on the size and/or duration time of the expected pump peak.

In an example, the controller may control to open the first bypass control valve when it is determined that the pump peak occurs based on a positional signal of the actuator or a pressure signal of a working oil supply line.

In an embodiment, when no sudden stop manipulation of the at least one actuator occurs, the controller may control to close the first bypass control valve. In an embodiment, the controller may control to open the first bypass control valve in advance of determining the sudden stop manipulation occurrence by a predetermined minimum area when an amount of the working oil discharged from the first hydraulic pump is greater than a predetermined value.

In an embodiment, the controller may control to open the first bypass valve at an initial engine ignition time or a warm up after ignition of the construction machinery.

In an embodiment, the controller may control to close the first bypass control valve during a multiple operation of the actuators even in case of the sudden stop manipulation of one of the actuators.

In an embodiment, the control system for construction machinery may further include a first electromagnetic proportional control valve to apply a pilot pressure corresponding to the control signal inputted from the controller to control the opening area of the first bypass control valve.

In an embodiment, the control system for construction machinery may further include a second hydraulic pump, a second control valve installed in a second center bypass line connected to the second hydraulic pump and configured to control a flow direction of a working oil discharged from the second hydraulic pump to selectively supply the working oil to a second actuator, a second bypass control valve installed downstream from the second control valve in the second center bypass line to variably control an amount of the working oil draining to a drain tank through the second center bypass line, and a second electromagnetic proportional control valve to apply a pilot pressure corresponding to the control signal inputted from the controller to control an opening area of the second bypass control valve.

In an example not belonging to the invention, the control system for construction machinery may further include a pump regulator configured to adjust a swash plate angle of the hydraulic pump according to the control signal inputted from the controller.

The present invention provides a control method for construction machinery according to claim <NUM>.

In an embodiment, the control method for construction machinery may further include determining an opening area of the bypass control valve based on the size and/or duration time of the pump peak that is expected to occur when the sudden stop manipulation of the at least one actuator occurs; and outputting a control signal for opening the bypass control valve according to the determined opening area to prevent the pump peak when the sudden stop manipulation occurs.

In an embodiment, the control method for construction machinery may further include closing the bypass control valve in case of no sudden stop manipulation.

In example embodiments, the control method for construction machinery may further include opening the bypass control valve in advance of determining the sudden stop manipulation occurrence by a predetermined minimum area when an amount of the working oil discharged from the hydraulic pump is greater than a predetermined value.

In an embodiment, the control method for construction machinery may further include opening the bypass control valve at an initial engine ignition time or a warm up after ignition of the construction machinery.

In an embodiment, the control method for construction machinery may further include closing the bypass control valve during a multiple operation of the actuators even in case of the sudden stop manipulation.

In an embodiment, opening the bypass control valve may include applying a pilot pressure for opening the bypass control valve according to the determined opening area, to the bypass control valve through an electromagnetic proportional control valve.

In an example not belonging to the invention, the control method for construction machinery may further include controlling a swash plate angle of the hydraulic pump according to the manipulation signal of an operator of the actuator.

According to embodiments, in case of a joystick sudden stop manipulation, a bypass control valve installed in a center bypass line may be opened such that a working oil discharged from a hydraulic pump may return to a drain tank through the center bypass line. In case of no joystick sudden stop manipulation, the bypass control valve may be closed.

Thus, in a closed center type of a hydraulic system, in case of the joystick sudden stop manipulation, a pump peak which occurs due to physical dynamic characteristic differences between the hydraulic pump and the control valve may be prevented.

However, the effect of the invention may not be limited thereto, and may be expanded without being deviated from the scope of the present invention.

Hereinafter, preferable embodiments of the present invention will be explained in detail with reference to the accompanying drawings.

In the drawings, the sizes and relative sizes of components or elements may be exaggerated for clarity.

It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of example embodiments.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of example embodiments.

Embodiments may, however, be embodied in many different forms and should not be construed as limited to Embodiments set forth herein. Rather, these Embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example embodiments to those skilled in the art.

<FIG> is a hydraulic circuit diagram illustrating a control system for construction machinery in accordance with an example. <FIG> is a block diagram illustrating a controller of the control system in <FIG>. <FIG> is a hydraulic circuit diagram illustrating the control system in a single operation of an actuator in <FIG>. <FIG> is a hydraulic circuit diagram illustrating the control system in a sudden stop operation of an actuator in <FIG>. <FIG> is graphs illustrating an opening area of a bypass control valve and a pump discharge amount in the sudden stop operation of the actuator in <FIG>.

Referring to <FIG>, a control system for construction machinery may include a first hydraulic pump <NUM>, at least one control valve <NUM>, <NUM> configured to control a flow direction of a working oil discharged from the first hydraulic pump <NUM> to control actuators <NUM>, <NUM>, a first bypass control valve <NUM> installed in a first center bypass line <NUM> downstream from the control valve to variably control an amount of the working oil draining to a drain tank T through the first center bypass line <NUM>, and a controller <NUM> configured to control operations of the first hydraulic pump <NUM>, the at least one control valve <NUM>, <NUM> and the first bypass control valve <NUM> according to pump peak occurrence.

In an example, the construction machinery may include an excavator, a wheel loader, a forklift, etc. Hereinafter, it will be explained that embodiments may be applied to the excavator. However, it may not be limited thereto, and it may be understood that embodiments may be applied to other construction machinery such as the wheel loader, the forklift, etc..

The construction machinery may include a lower travelling body, an upper swinging body mounted to be capable of swinging on the lower travelling body, and a cabin and a front working device installed in the upper swinging body. The front working device may include a boom, an arm and a bucket. A boom cylinder for controlling a movement of the boom may be installed between the boom and the upper swinging body. An arm cylinder for controlling a movement of the arm may be installed between the arm and the boom. A bucket cylinder for controlling a movement of the bucket may be installed between the bucket and the arm. As the boom cylinder, the arm cylinder and the bucket cylinder expand or contract, the boom, the arm and the bucket may implement various movements, to thereby perform various works.

In example, the first hydraulic pump <NUM> may be connected to an electric motor (not illustrated) or an engine (not illustrated) through a power transferring device such that a power of the engine may be transferred to the first hydraulic pump <NUM>.

For example, the first hydraulic pump <NUM> may include a pressure control type electronic hydraulic pump. A discharged amount of the first hydraulic pump <NUM> may be determined by a swash plate angle. The swash plate angle of the first hydraulic pump <NUM> may be adjusted according to a pump control signal inputted from the controller <NUM>.

In particular, the swash plate angle of the first hydraulic pump <NUM> may be adjusted by a first pump regulator <NUM>. The first pump regulator <NUM> may be connected to a pilot pump (not illustrated) via a third electromagnetic proportional control valve <NUM>. The pilot pump may be connected to an output axis of the engine, and as the output axis of the engine rotates, the pilot pump may be driven to discharge a pilot working oil. For example, the pilot pump may include a gear pump. In this case, the working oil and the pilot working oil may include substantially the same material.

The pilot working oil may be supplied to the first pump regulator <NUM> through the third electromagnetic proportional control valve <NUM>. The third electromagnetic proportional control valve <NUM> may adjust the swash plate angle of the first hydraulic pump <NUM> by applying a pilot pressure corresponding to the inputted pump control signal to the first pump regulator <NUM> to. Accordingly, a discharge pressure of the first hydraulic pump <NUM> may be determined according to a current command value of the pump control signal.

In an embodiment, the working oil discharged from the first hydraulic pump <NUM> may be supplied to the first and third actuators <NUM> and <NUM> through the first and third control valves <NUM> and <NUM> respectively.

In particular, the first and third control valves <NUM> and <NUM> may be connected to the first hydraulic pump <NUM> through a first main hydraulic line <NUM>. The first main hydraulic line <NUM> may be divided into a first center bypass line <NUM> and a parallel supply line <NUM>. The first and third control valves <NUM>, <NUM> may be installed sequentially in series in the first center bypass line <NUM>.

The first main hydraulic line <NUM> may be divided into the first center bypass line <NUM> and at least one parallel line <NUM>, and the third control valve <NUM> may be connected to at least one of the first center bypass line <NUM> and the parallel line <NUM>. Even though the first control valve <NUM> is switched to close the first center bypass line <NUM>, the third control valve <NUM> may be connected to the first hydraulic pump <NUM> by the parallel line <NUM> such that the working oil discharged from the first hydraulic pump <NUM> may be supplied to the third control valve <NUM>.

Although it is not illustrated in the figures, an auxiliary control valve for controlling an operation of a third actuator may be installed in the first center bypass line <NUM>, and the working oil discharged from the first hydraulic pump <NUM> may be supplied to the third actuator through the auxiliary control valve.

In example embodiments, the first actuator <NUM> may be the boom cylinder, and the third actuator <NUM> may be the arm cylinder. In this case, the first control valve <NUM> may be a boom control valve, and the third control valve <NUM> may be an arm control valve.

The first control valve <NUM>, that is, the boom control valve may be connected to the first actuator <NUM>, that is, a boom head chamber and a boom rod chamber of the boom cylinder through hydraulic lines. Accordingly, the first control valve <NUM> may be switched to selectively supply the working oil discharged from the first hydraulic pump <NUM> to the boom head chamber and the boom rod chamber. The working oil which drives the boom cylinder <NUM> may return to the drain tank T through a return hydraulic line <NUM>.

The third control valve <NUM>, that is, the arm control valve may be connected to the third actuator <NUM>, that is, an arm head chamber and an arm rod chamber of the arm cylinder <NUM> through hydraulic lines. Accordingly, the third control valve <NUM> may be switched to selectively supply the working oil discharged from the first hydraulic pump <NUM> to the arm head chamber and the arm rod chamber. The working oil which drives the arm cylinder <NUM> may return to the drain tank T through a return hydraulic line <NUM>.

In example embodiments, the control system for construction machinery may include a main control valve (MCV) as an assembly including the first and third control valves <NUM> and <NUM>. The main control valve may include at least portions of the first center bypass line <NUM>, the return lines <NUM>, <NUM> and the parallel lines <NUM> therein, and may be provided as one package product including the first and third control valves <NUM>, <NUM> installed sequentially therein. The main control valve may be an electro-hydraulic main control valve including an electro proportional pressure reducing valve (EPPRV) which controls a pilot working oil supplied to a spool of the control valve according to an inputted electrical signal. Alternatively, the main control valve may include a hydraulic control valve which is controlled by a pilot working oil in proportion to a manipulation signal.

In embodiment, the first bypass control valve <NUM> may be installed downstream from the third control valve <NUM> in the first center bypass line <NUM>, and may variably control the amount of the working oil draining to the drain tank T through the first center bypass line <NUM>.

In particular, the first bypass control valve <NUM> may be connected to the pilot pump via a first electromagnetic proportional control valve <NUM>. The pilot working oil discharged from the pilot pump may be supplied to the first bypass control valve <NUM> through the first electromagnetic proportional control valve <NUM>. The first electromagnetic proportional control valve <NUM> may apply a pilot pressure corresponding to a bypass control signal from the controller <NUM> to the first bypass control valve <NUM> to adjust an opening area of the first bypass control valve <NUM>. For example, the first electromagnetic control valve may include an electro proportional pressure reducing valve (EPPRV). The first electromagnetic proportional control valve may generate a pilot signal pressure in proportion to an intensity of the received control signal, for example, current intensity.

When the bypass control signal is not inputted to the first electromagnetic proportional control valve <NUM>, the first bypass control valve <NUM> may be closed. In this case, when there are no manipulation signals for the first and third actuators <NUM>, <NUM>, the working oil from the first hydraulic pump <NUM> may not return to the drain tank T through the first center bypass line <NUM>.

When the bypass control single is inputted to the first electromagnetic proportional control valve <NUM>, the first bypass control valve <NUM> may be opened by an opening area corresponding to the inputted bypass control signal. In this case, when there are no manipulation signals for the first and third actuators <NUM>, <NUM>, the amount of the working oil discharged from the first hydraulic pump <NUM> and returning to the drain tank T through the first center bypass line <NUM> may correspond to the opening area.

In an example, the control system may further include a relief valve (not illustrated) which is installed upstream from the first bypass control valve <NUM> in the first main hydraulic line <NUM>. The relief valve may limit the pressure of the working oil discharged from the first hydraulic pump <NUM> to be under a predetermined allowable pressure. When the pressure of the main hydraulic line <NUM> is above the allowable pressure, the relief valve may be opened such that the pressure is maintained under the allowable pressure.

In an embodiment, the control system may further include a second hydraulic pump <NUM> for supplying a working oil to second and fourth actuators <NUM> and <NUM>, second and fourth control valves <NUM>, <NUM> configured to control a flow direction of the working oil discharged from the second hydraulic pump <NUM> to control the second and fourth actuators <NUM>, <NUM>, a second bypass control valve <NUM> installed in a second center bypass line <NUM> downstream from the second and fourth control valves <NUM>, <NUM> to variably control an amount of the working oil draining to the drain tank T through the second center bypass line <NUM>, a second pump regulator <NUM> configured to control a discharge pressure of the second hydraulic pump <NUM> in proportion to a pump control signal generated according to a manipulation signal of an operator, and a second electromagnetic proportional control valve <NUM> configured to control a spool displacement of the second bypass control valve <NUM> in proportion to a bypass control signal generated according to the manipulation signal of an operator.

Operations of the second pump regulator <NUM>, the second bypass control valve <NUM> and the second electromagnetic proportional control valve <NUM> may be substantially the same as those of the first pump regulator <NUM>, the first bypass control valve <NUM> and the first electromagnetic proportional control valve <NUM>, and thus, any further explanation concerning the above elements will be omitted.

In example embodiments, the controller <NUM> may receive the manipulation signal in proportion to a manipulation amount of an operator, and output a control signal (pump control signal, bypass control signal) corresponding to the manipulation signal to the third and first electromagnetic proportional control valves <NUM>, <NUM>. The third and first electromagnetic proportional control valves <NUM>, <NUM> may output a secondary pressure in proportion to the control signal, to control the first pump regulator <NUM> and the first bypass control valve <NUM> using electrical signals.

Additionally, in case of the electro-hydraulic main control valve, the controller <NUM> may output pressure command signals as the control signal to the electro proportional pressure reducing valves, respectively. The electro proportional pressure reducing valves may output a secondary pressure in proportion to the pressure command signal to spools of the corresponding control valve, to control the spools using electrical signals.

Alternatively, in case of the hydraulic main control valve, the pilot pressure from a manipulation portion <NUM> may be supplied to the spools of the first and second control valves, to control the first and second control valves.

For example, the manipulation portion <NUM> may include a joystick, a pedal, etc. When an operator manipulates the manipulation portion <NUM>, a manipulation signal corresponding to the manipulation may be generated. The controller <NUM> may receive the manipulation signal and control operations of the first hydraulic pump <NUM> and the first bypass control valve <NUM>.

In example embodiments, as illustrated in <FIG>, the controller <NUM> may include a sudden stop determiner <NUM> determining whether or not a sudden stop manipulation of an actuator occurs, based on a joystick manipulation signal generated when the joystick of the manipulation portion <NUM> is manipulated, a calculator <NUM> determining an opening area of the first bypass control valve <NUM> when the sudden stop manipulation of the actuator occurs, and an output portion <NUM> outputting a bypass control signal for opening the first bypass control valve <NUM> according to the calculated opening area.

The sudden stop determiner <NUM> may receive manipulation signals of the first and third actuators <NUM>, <NUM>, for example, joystick pilot pressure, joystick displacement amount, etc., and may determine that the sudden stop manipulation occurs when a decreasing inclination is greater than a predetermined value.

Additionally, the sudden stop determiner <NUM> may determine that the sudden stop manipulation does not occur when the decreasing inclination of the manipulation signal of any one of the actuators <NUM>, <NUM> during a multiple operation of the actuators <NUM>, <NUM> is less than the predetermined value.

The calculator <NUM> may predict a pump peak which occurs when the first center bypass line <NUM> is closed, and may calculate the opening area, an opening duration, a closing inclination, etc. of the first bypass control valve <NUM>, based on a size and duration time of the pump peak. For example, the calculator <NUM> may calculate the opening area of the first bypass control valve <NUM> according to the duration time of the predicted pump peak. The calculator <NUM> may determine the closing speed of the first bypass control valve <NUM> based on whether or not a secondary pump peak occurs when the first bypass control valve <NUM> is closed again.

Additionally, the calculator <NUM> may receive a swash plate angle, a discharge pressure, etc. of the first hydraulic pump <NUM> from a pump swash plate angle sensor <NUM> and a pump discharge pressure sensor <NUM>, and may determine a minimum opening area of the first bypass control valve <NUM> when the amount of the working oil discharged from the hydraulic pump <NUM> is greater than a predetermined value.

The output portion <NUM> may output the bypass control signal for opening the first bypass control valve <NUM> according to the calculated opening area. The output portion <NUM> may output the bypass control signal corresponding to the opening area, the opening time and the closing inclination of the first bypass control valve <NUM> in case of the sudden stop manipulation.

The first electromagnetic proportion control valve <NUM> may supply a pilot signal pressure for controlling the opening area of the first bypass control valve <NUM> according to a control signal inputted from the output portion <NUM>.

Thus, in case of the sudden stop manipulation of the actuator, the first bypass control valve <NUM> may be opened by the calculated opening area and then may be closed at the calculated closing inclination. In case of no sudden stop manipulation of the actuator, the first bypass control valve <NUM> may be maintained to be closed.

Additionally, when the amount of the working oil discharged from the first hydraulic pump <NUM> is greater than the predetermined value before the sudden stop manipulation of the actuator, the first bypass control valve <NUM> may be opened in advance by the predetermined minimum area. As such, in case that the first bypass control valve <NUM> is opened in advance by the minimum predetermined area, the first bypass control valve <NUM> may be opened rapidly in the sudden stop manipulation of the actuator. Thus, a response speed of the first bypass control valve <NUM> may be improved more. In this case, the first hydraulic pump <NUM> may be controlled such that the amount of the working oil to be discharged may be greater than the predicted amount in consideration that the first bypass control valve <NUM> is opened in advance.

As illustrated in <FIG>, when the joystick of the manipulation portion <NUM> corresponding to the third actuator <NUM> is manipulated, the third control valve <NUM> may be switched and the working oil discharged from the first hydraulic pump <NUM> may be supplied to the third actuator <NUM>. In here, the first bypass control valve <NUM> may be maintained to be closed or be opened by the minimum opening area.

As illustrated in <FIG>, in case of the sudden stop manipulation of the third actuator <NUM>, the third control valve <NUM> may return to a neutral position, and the first bypass control valve <NUM> may be opened by a calculated opening area. Additionally, the swash plate angle of the first hydraulic pump <NUM> may be decreased according to the pump control signal such that the discharge amount of the working oil may be decreased.

Referring to <FIG>, graphs of the pilot pressure A at the spool of the control valve, the pump pressure B, the opening area C of the first bypass control valve <NUM> and the pump discharge amount D in case of the joystick sudden stop manipulation are illustrated.

As an operator starts to manipulate the joystick for driving the actuator, the pilot pressure A may be increased. Then, at the joystick sudden stop manipulation (t2), the pilot pressure A may drop sharply, the spool of the control valve may return rapidly to the neutral position. If the first center bypass line <NUM> is closed by the first bypass control valve <NUM>, the pressure of the first center bypass line <NUM>, that is, pump pressure B generated by the working oil discharged from the hydraulic pump <NUM> may rise sharply so that the pump peak occurs.

In example embodiments, the controller <NUM> may open the first bypass control valve <NUM> in advance by the minimum opening area A1 at times (t0 - t2) before the joystick sudden stop manipulation. The controller <NUM> may open the first bypass control valve <NUM> by the predetermined opening area (A2) at the joystick sudden stop manipulation (t2 - t3) and then may close at a constant inclination (t3 - t4).

There may be physical dynamic characteristic differences between the first hydraulic pump <NUM> and the control valve. In particular, because the response time of the control valve is relatively faster than the response time of the first hydraulic pump <NUM>, in case of the sudden stop manipulation even though the control valve returns already to the neutral position, the working oil may be discharged from the first hydraulic pump <NUM> so that the pump discharge pressure may rise rapidly. In here, the first bypass control valve <NUM> may be opened rapidly such that the discharged working oil may return to the drain tank T through the first bypass control valve <NUM>, to thereby prevent the pump peak which may occur in the main hydraulic line <NUM> in case of the sudden stop manipulation.

In example embodiments, the control system for construction machinery may further sensors installed in the working oil supply line such as the first and second main hydraulic lines <NUM>, <NUM> to detect pressures, and sensors for detecting positions, angles, pressures, etc. of the first to fourth actuators <NUM>, <NUM>, <NUM>, <NUM>. For example, the sensor may detect the pressure of the working oil supply line or the position of the actuators. In this case, the controller <NUM> may receive the pressure signal of the working oil supply line or the position signal of the actuator, and may determine whether or not a pump peak occurs due to external impacts or loads.

For example, if the bucket encounters rock in a ground during an excavation operation, a pump peak may occur due to a load exerted on the bucket cylinder. In here, the controller <NUM> may determine whether or not the pump peak occurs according to the pressure increase in the working oil supply line or the sudden stop of the actuator. That is, when it is determined that the actuator stops suddenly by the external load, the controller <NUM> may determine that the pump peak occurs, and may output the bypass control signal to the first electromagnetic control valve <NUM>. When the bypass control signal is inputted to the first electromagnetic control valve <NUM>, the first bypass control valve <NUM> may be opened by the opening area corresponding to the inputted bypass control signal, to thereby prevent the pump pressure peak.

<FIG> is a hydraulic circuit diagram illustrating a control system for construction machinery in accordance with a comparative example embodiment.

Referring to <FIG>, a control system for construction machinery in accordance with a comparative example embodiment may include first and second bypass valves <NUM>, <NUM> installed in first and second center bypass lines <NUM>, <NUM> respectively, and a solenoid valve <NUM> for opening and closing the first and second bypass valves <NUM>, <NUM>. Additionally, the control system for construction machinery in accordance with a comparative example embodiment may include first and second pump peak reducing valves <NUM>, <NUM> installed in first and second main hydraulic lines <NUM>, <NUM> respectively to evacuate the working oil discharged from the first and second hydraulic pumps <NUM>, <NUM> to thereby prevent a pump peak.

In the control system for construction machinery in accordance with a comparative example embodiment, the solenoid valve <NUM> may be turned ON at an initial engine ignition time or a warm up after ignition to open the first and second center bypass lines <NUM>, <NUM>, and may be tuned OFF during a general operation to close the first and second center bypass lines <NUM>, <NUM>.

Thus, because the first and second center bypass lines <NUM>, <NUM> are closed in case of the joystick sudden stop manipulation, the pressure of the working oil discharged from the first and second hydraulic pumps <NUM>, <NUM> may rise rapidly. And then, the first and second pump peak reducing valves <NUM>, <NUM> may evacuate the working oil discharged from the first and second hydraulic pumps <NUM>, <NUM> late to reduce the increased pump pressure. The first and second center bypass lines <NUM>, <NUM> may be opened and closed by one solenoid valve <NUM>.

On the contrary, in the control system of construction machinery in accordance with example embodiments, as illustrated in <FIG>, the opening areas of the first and second center bypass lines <NUM>, <NUM> may be adjusted by the first and second electromagnetic proportional valves <NUM>, <NUM> respectively. In case of the joystick sudden stop manipulation, whether or not the sudden stop manipulation occurs may be determined through manipulation signals of the joystick in advance and then the first and second center bypass lines <NUM>, <NUM> may be opened to remove the pump peak. Accordingly, a center bypass line control of each of the first and second hydraulic pumps <NUM>, <NUM> may be performed independently, to prevent unnecessary flow loss. Further, the first and second electromagnetic proportional control valves <NUM>, <NUM> may perform functions to temporarily open the first and second center bypass lines <NUM>, <NUM> at the initial engine ignition time or the warm up after ignition similarly to the comparative example embodiment. However, differently to the comparative example embodiments using the solenoid valve, in example embodiments, the electromagnetic proportional control valve may be used to prevent the bypass lines from being opened rapidly or more than needed.

Hereinafter, a control method for construction machinery using the control system in <FIG> will be explained.

<FIG> is a flow chart illustrating a control method for construction machinery in accordance with example embodiments.

Referring to <FIG>, <FIG> and <FIG>, a manipulation signal of an operator for first and third actuators <NUM> and <NUM> and a discharge pressure and a swash plate angle of a first hydraulic pump <NUM> may be received (S100), and then, whether or not a sudden stop manipulation occurs may be determined based on the manipulation signal (S <NUM>). Then, in case of the sudden stop manipulation, a first bypass control valve <NUM> may be opened (S <NUM>), and in case of no sudden stop manipulation, the first bypass control valve <NUM> may be closed (S <NUM>).

In example embodiments, the manipulation signals for the first and third actuators <NUM>, <NUM>, for example, joystick pilot pressure, joystick displacement amount, etc., may be received, and it may be determined that the sudden stop manipulation occurs when a decreasing inclination is greater than a predetermined value.

Additionally, it may be determined that the sudden stop manipulation does not occur when the decreasing inclination of the manipulation signal for any one of the actuators <NUM>, <NUM> during a multiple operation of the actuators <NUM>, <NUM> is less than the predetermined value.

In here, a pump peak which occurs in case of the sudden stop manipulation when the first center bypass line <NUM> is closed may be predicted, and an opening area, an opening duration time, a closing inclination, etc. of the first bypass control valve <NUM> may be calculated based on a size and duration time of the pump peak. For example, the opening area of the first bypass control valve <NUM> according to the duration time of the predicted pump peak may be calculated. The closing speed of the first bypass control valve <NUM> may be determined based on whether or not a secondary pump peak occurs when the first bypass control valve <NUM> is closed again.

Additionally, the swash plate angle and the discharge pressure of the first hydraulic pump <NUM> may be used to calculate a minimum opening area of the first bypass control valve <NUM> when the amount of the working oil discharged from the first hydraulic pump <NUM> is greater than a predetermined value.

In case of the sudden stop manipulation, the first bypass control valve <NUM> may be opened by the calculated opening area and then may be closed at the calculated closing inclination. When the amount of the working oil discharged from the first hydraulic pump <NUM> is greater than the predetermined value before the sudden stop manipulation, the first bypass control valve <NUM> may be opened in advance by the minimum predetermined area. In case of no sudden stop manipulation, the first bypass control valve <NUM> may be maintained to be closed.

As mentioned above, in case of the joystick sudden stop manipulation, the first bypass control valve <NUM> installed downstream from the main control valve in the center bypass line <NUM> is opened such that the working oil discharged from the first hydraulic pump <NUM> returns to the drain tank T through the first center bypass line <NUM>. In case of no joystick sudden stop manipulation, the first bypass control valve <NUM> may be closed.

Thus, in a closed center type of a hydraulic system, in case of the joystick sudden stop manipulation, the pump peak which occurs due to physical dynamic characteristic differences between the hydraulic pump and the control valve may be prevented.

Claim 1:
A control system for construction machinery, comprising:
a first hydraulic pump (<NUM>);
at least one control valve (<NUM>, <NUM>) installed in a first center bypass line (<NUM>) connected to the first hydraulic pump (<NUM>), and configured to control a flow direction of a working oil discharged from the first hydraulic pump (<NUM>) to selectively supply the working oil to at least one actuator (<NUM>, <NUM>);
a first bypass control valve (<NUM>) installed downstream from the at least one control valve (<NUM>, <NUM>) in the first center bypass line (<NUM>) to variably control an amount of the working oil draining to a drain tank (T) through the first center bypass line (<NUM>); and
a controller (<NUM>) configured to control operations of the first hydraulic pump (<NUM>) and the first bypass control valve (<NUM>) according to a manipulation signal of an operator,
wherein the controller (<NUM>) is configured to
determine whether or not a sudden stop manipulation of the at least one actuator (<NUM>, <NUM>) occurs based on a joystick manipulation signal of the operator, and
open the first bypass control valve (<NUM>) to prevent a pump peak when the sudden stop manipulation occurs.