Hydraulic control device and hydraulic control method for construction machine

A hydraulic control apparatus for construction machinery, includes an accumulator to accumulate a high-pressure hydraulic oil discharged from a boom cylinder for driving a boom of the construction machinery, a hydraulic pump connected to the accumulator and driven by the high-pressure hydraulic oil, a pressure sensor configured to detect a pressure of the accumulator, and a control unit connected to the accumulator and the hydraulic motor and configured to control operations of the accumulator and the hydraulic motor, and having a determiner that receives a pressure value of the accumulator and number of revolution of the hydraulic motor to determine whether or not the hydraulic motor fails when the hydraulic oil accumulated in the accumulator is supplied to the hydraulic motor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage of International Application No. PCT/KR2016/005791, filed on Jun. 1, 2016, which claims priority to Korean Patent Application No. 10-2015-0172641, filed on Dec. 4, 2015, the entire contents of each of which are being incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a hydraulic control apparatus and a hydraulic control method for construction machinery, more particularly, to a hydraulic control apparatus including a regeneration device for regenerating boom energy in construction machinery and a hydraulic control method.

BACKGROUND ART

Construction machinery may raise and lower a front work apparatus using a hydraulic cylinder to. For example, an engine power may be used to drive a hydraulic pump, and a hydraulic oil discharged from the hydraulic pump may be supplied to a boom cylinder through a main control valve to generate stoke of the boom cylinder, thereby raising a boom. On the other hand, when the boom is lowered, the hydraulic oil from the boom cylinder may be drained to a drain tank through the main control valve due to gravity of the front work apparatus. During the boom down operation, potential energy of the front work apparatus may not be effectively utilized. Accordingly, a new technique of regenerating the potential energy may have been developed.

Especially, even if a regeneration device such as a hydraulic motor for regenerating the boom energy has abnormality and thus cannot operate normally, the boom cylinder should be controlled to operate normally.

DISCLOSURE OF THE INVENTION

Problems to be Solved

An object of the present invention provides a hydraulic control apparatus for construction machinery capable of effectively regenerating boom energy of the construction machinery.

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

Means to Solve the Problems

According to example embodiments, a hydraulic control apparatus for construction machinery, includes an accumulator to accumulate a high-pressure hydraulic oil discharged from a boom cylinder for driving a boom of the construction machinery, a hydraulic pump connected to the accumulator and driven by the high-pressure hydraulic oil, a pressure sensor configured to detect a pressure of the accumulator, and a control unit connected to the accumulator and the hydraulic motor and configured to control operations of the accumulator and the hydraulic motor, and having a determiner that receives a pressure value of the accumulator and number of revolution of the hydraulic motor to determine whether or not the hydraulic motor fails when the hydraulic oil accumulated in the accumulator is supplied to the hydraulic motor.

In example embodiments, the determiner may include a first calculator to calculate a volume change of the accumulator from the pressure value of the accumulator, a second calculator to calculate a flow rate of the hydraulic oil flowing through the hydraulic motor from the number of revolution of the hydraulic motor, and a compares to compare the volume change and the flow rate to determine a failure in the hydraulic motor and output a control signal.

In example embodiments, the hydraulic motor may include a variable displacement hydraulic motor.

In example embodiments, when it is determined that the hydraulic motor fails, the control unit may control such that the hydraulic oil discharged from the boom cylinder is blocked from being supplied to the hydraulic motor and a pilot pressure from a manipulation portion is supplied to a main control valve.

In example embodiments, the hydraulic oil discharged from a boom head chamber of the boom cylinder may be drained to a drain tank through the main control valve.

In example embodiments, when it is determined that the hydraulic motor operates normally, the control unit may control such that a pilot pressure from a manipulation portion is blocked from being transferred to a main control valve.

In example embodiments, the hydraulic control apparatus for construction machinery may further include a bypass valve provided between the manipulation portion and the main control valve to block the pilot pressure from being transferred to the main control valve.

In example embodiments, the accumulator and the hydraulic motor may be connected to a boom head chamber of the boom cylinder through a hydraulic regeneration line.

In example embodiments, the hydraulic control apparatus for construction machinery may further include a regeneration valve unit installed in the hydraulic regeneration line, and the regeneration valve unit may include a discharge amount control valve to control an amount of the hydraulic oil flowing through the hydraulic regeneration line.

In example embodiments, the hydraulic motor may be connected to a drive axis of an engine to provide a rotational force to a hydraulic pump that supplies the hydraulic oil to the boom cylinder.

According to example embodiments, in a hydraulic control method for construction machinery, a hydraulic oil accumulated in an accumulator is supplied to a hydraulic motor so as to regenerate energy of the hydraulic oil discharged from a boom cylinder of the construction machinery. A volume change of the accumulator and a flow rate of the hydraulic oil flowing through the hydraulic motor are calculated. The volume change and the flow rate are compared to determine whether or not the hydraulic motor fails.

In example embodiments, calculating the volume change of the accumulator and the flow rate of the hydraulic oil flowing through the hydraulic motor may include detecting a pressure of the accumulator to calculate the volume change of the accumulator, and calculating the flow rate of the hydraulic oil flowing through the hydraulic motor from number of revolution of the hydraulic motor.

In example embodiments, the hydraulic control method for construction machinery may further include when it is determined that the hydraulic motor fails, blocking the hydraulic oil discharged from the boom cylinder from being supplied to the hydraulic motor and supplying a pilot pressure from a manipulation portion to a main control valve.

In example embodiments, the hydraulic control method for construction machinery may further include draining the hydraulic oil discharged from a boom head chamber of the boom cylinder to a drain tank through the main control valve.

In example embodiments, the hydraulic control method for construction machinery may further include when it is determined that the hydraulic motor operates normally, blocking a pilot pressure from a manipulation portion from being transferred to a main control valve.

In example embodiments, the hydraulic control method for construction machinery may further include supplying the hydraulic oil from a boom head chamber of the boom cylinder to the accumulator or the hydraulic motor through a hydraulic regeneration line.

In example embodiments, the hydraulic motor may be connected to a drive axis of an engine to provide a rotational force to a hydraulic pump that supplies the hydraulic oil to the boom cylinder.

Effects of the Invention

According to example embodiments, in a hydraulic control apparatus and a hydraulic control method for construction machinery, a calculated volume change due to a pressure change in an accumulator and a theoretical flow rate value of a hydraulic motor may be calculated to determine whether or not the hydraulic motor fails.

Accordingly, because an extra swash plate sensor for detecting a failure in the hydraulic motor is not needed, a design modification of the hydraulic motor may not be required, and whether or not the hydraulic motor fails may be determined using software calculation. When it is determined that the hydraulic motor fails, a boom energy regeneration device may discontinue to operate and an operator may be notified of an alarm signal for rapid repairs.

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

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferable embodiments of the present invention will be explained in detail with reference to the accompanying drawings. Like numerals refer to like elements throughout example embodiments, and any further repetitive explanation concerning the similar elements will be omitted.

FIG. 1is a side view illustrating construction machinery in accordance with example embodiments.FIG. 2is a hydraulic circuit diagram illustrating a hydraulic system for construction machinery in accordance with example embodiments.FIG. 3is a block diagram illustrating a determiner configured to determine a failure in a regeneration device of the hydraulic system inFIG. 2.

Referring toFIGS. 1 to 3, construction machinery10may include a lower travelling body20, an upper swing body30mounted rotatably on the lower travelling body20, and a cabin50and a front work apparatus60installed in the upper swing body30.

The lower travelling body20may support the upper swing body30, and may use a driving force generated by an engine100to travel the construction machinery10such as an excavator. The lower travelling body20may be a crawler type travelling body having a track shoe assembly. Alternatively, the lower travelling body20may be a wheel type travelling body including driving wheels. The upper swing body30may include an upper frame32as a base, and may rotate on a plane parallel with a ground to determine a working direction. The cabin50may be installed in a left front portion of the upper frame32, and the front work apparatus60may be installed in a front body of the upper frame32.

The front work apparatus60may include a boom70, an arm80and a bucket90. A boom cylinder72may be installed between the boom70and the upper frame32to control a movement of the boom70. An arm cylinder82may be installed between the arm80and the boom70to control a movement of the arm80. A bucket cylinder92may be installed between the bucket90and the arm80to control a movement of the bucket90. As the boom cylinder72, the arm cylinder82and the bucket cylinder92expand or contract, the boom70, the arm80and the bucket90may implement various movements, so that the front work apparatus60may perform various works. The boom cylinder72, the arm cylinder82and the bucket cylinder92may expand or contract by a hydraulic oil supplied from a hydraulic pump200,202.

In addition, an energy regeneration system may be provided to regenerate boom energy which is wasted from the boom cylinder72when the boom70is lowered. The energy regeneration system may include a regeneration valve unit400having a plurality of valves.

The energy regeneration system may accumulate the hydraulic oil, which is discharged from the boom cylinder72when the boom70is lowered, in an accumulator500or to supply the hydraulic oil to a hydraulic motor510to thereby assist an output of the engine, as described later.

As illustrated inFIG. 2, a hydraulic system of construction machinery in accordance with example embodiments, may include at least one hydraulic pump200,202connected to the engine100, at least one actuator72,82,92configured to operate the front work apparatus, a main control valve (MCV)300installed between the hydraulic pump and the actuator to control an operation of the actuator, a regeneration device configured to regenerate energy of the front work apparatus, and a control unit600configured to control an operation of the front work apparatus.

In example embodiments, the engine100may include a diesel engine as a driving source for a construction machine, for example, excavator. At least one hydraulic pump200,202may be connected to the engine100through a power take off (PTO). Although it is not illustrated in the figures, a pilot pump or additional hydraulic pumps may be connected to the engine100. Accordingly, a power of the engine100may be transferred to the hydraulic pump200,202and the pilot pump.

The hydraulic pump200,202may be connected to the main control valve300through a hydraulic line210. The main control valve300may supply a hydraulic oil which is discharged from the hydraulic pump200,202, to the actuator such as the boom cylinder72, arm cylinder82, the bucket cylinder92, etc.

The main control valve300may be connected to a plurality of actuators including the boom cylinder72, the arm cylinder82and the bucket cylinder92through a high-pressure hydraulic line220, respectively. Accordingly, the actuators such as the boom cylinder, the arm cylinder and the bucket cylinder may be driven by the hydraulic oil discharged from the hydraulic pump200,202.

For example, a boom control spool310may be connected to a boom head chamber72aand a boom rod chamber72bby a boom head hydraulic line222and a boom rod hydraulic line224respectively. Accordingly, the boom control spool310may be switched to selectively supply the hydraulic oil discharged from the hydraulic pump200to the boom head chamber72aand the boom rod chamber72b.

The hydraulic oil which drives the actuator may return to a drain tank T through a return hydraulic line212. In example embodiments, when the boom is lowered, the hydraulic oil from the boom head chamber72amay be drained to the drain tank T through the boom head hydraulic line222via the boom control spool310. When the boom is raised, the hydraulic oil from the boom rod chamber72bmay be drained to the drain tank T through the boom rod hydraulic line224via the boom control spool310.

In example embodiments, the hydraulic system for construction machinery may include the regeneration valve unit400which is installed in a hydraulic regeneration line230connected to the boom head chamber72ato control a supply of the hydraulic oil to the regeneration device. The regeneration valve unit may include a discharge amount control valve410, a check valve420and an auxiliary flow control valve430. However, it may not be limited thereto, and the regeneration valve unit may have various valves adapted for the energy regeneration system.

The hydraulic regeneration line230may be connected to the boom head chamber72a. A hydraulic line from a boom lock valve76may branch into the boom head hydraulic line222and the hydraulic regeneration line230. The discharge amount control valve410may be installed in the hydraulic regeneration line230to control an amount of the hydraulic oil flowing through the hydraulic regeneration line230. The check valve420for holding the boom70may be installed in the hydraulic regeneration line230in front of the discharge amount control valve410to selectively open and close the hydraulic regeneration line230. An opening/closing valve430may be installed in a connection line240which connects the hydraulic regeneration line230to the boom rod chamber72b, to selectively supply a portion of the hydraulic oil discharged through the hydraulic regeneration line230to the boom rod chamber72bof the boom cylinder72.

In example embodiments, the control unit600may output a pilot signal pressure to the regeneration valve unit to control supplying of the hydraulic oil to the regeneration device through the hydraulic regeneration line230. The control unit600may include a controller to apply electrical signals and first to third control valves to output pilot signal pressures corresponding to the applied electrical signals.

In particular, the first control valve may apply a pilot signal pressure corresponding to an electrical signal applied from the controller, to the discharge amount control valve410. The first control valve may include an electro proportional pressure reducing valve (EPPRV). The pilot signal pressure outputted from the first control valve may be supplied to a left port of the discharge amount control valve410to switch to the right direction inFIG. 2, to thereby open the hydraulic regeneration line230. An opening area of the discharge amount control valve410through which the hydraulic oil passes may be changed according to a position of a control spool. Accordingly, the discharge amount control valve410may control opening/closing of the hydraulic regeneration line230or the amount of the hydraulic oil passing through the hydraulic regeneration line230.

The second control valve may apply a pilot signal pressure corresponding to an electrical signal applied from the controller, to the check valve420. The first control valve may include an electro proportional pressure reducing valve (EPPRV). The pilot signal pressure outputted from the second control valve may be supplied to the check valve420to open the hydraulic regeneration line230. The check valve420may be a pilot-operated check valve which is held open by the pilot signal pressure. Alternatively, the second control valve may be a solenoid valve. In this case, the check valve420may be opened/closed by ON/OFF signal of the solenoid valve.

The third control valve may apply a pilot signal pressure corresponding to an electrical signal applied from the controller, to the opening/closing valve430. The third control valve may include an electro proportional pressure reducing valve (EPPRV). The pilot signal pressure outputted from the third control valve may be supplied to a left port of the opening/closing valve430to switch to the right direction inFIG. 2, to thereby open the connection line240. Thus, as the boom rod chamber72bis connected to the hydraulic regeneration line230through the connection line240, insufficient flow rates due to an area difference between the head side and the rod side of the boom cylinder when the boom is lowered, may be supplied to the boom rod chamber72bof the boom cylinder72.

In example embodiments, the regeneration device may regenerate energy using the high-pressure hydraulic oil discharged from the boom head chamber72aof the boom cylinder72. The regeneration device may include an accumulator500and a hydraulic motor510. A distal end of the hydraulic regeneration line230may branch to be connected to the accumulator500and the hydraulic motor510.

The accumulator500may accumulate the high-pressure hydraulic oil which is discharged from the boom head chamber72aof the boom cylinder72when the boom is lowered. An opening/closing valve502may be installed in the hydraulic regeneration line230connected to the accumulator500to control supplying/discharging of the hydraulic oil to/from the accumulator500.

In particular, the control unit may include a fourth control valve to output a pilot signal pressure corresponding to an applied electrical signal, and the fourth control valve may output the pilot signal pressure to the opening/closing valve502. The fourth control valve may include an electro proportional pressure reducing valve (EPPRV). The opening/closing valve502may be switched by the pilot signal pressure outputted from the fourth control valve, to control supplying/discharging of the hydraulic oil to/from the accumulator500.

The hydraulic motor510may be connected to a drive axis of the engine100to assist driving power of the engine. The hydraulic motor510may be connected to the drive axis of the engine100through the power take off (PTO) having a predetermined gear ratio.

In example embodiments, the main control valve300may include a hydraulic type control valve. The boom control spool310may be controlled by a pilot pressure in proportion to a manipulation signal of a manipulation portion52.

In particular, as an operator manipulates the manipulating portion52, the manipulation portion52may generate a pilot oil, which is discharged from the pilot pump, to have the pilot pressure in proportion to the manipulation signal and may supply the pilot oil to the boom control spool310through control lines. Accordingly, the boom control spool310may be displaced in proportion to the pilot pressure of the pilot oil, and thus, the hydraulic oil discharge from the hydraulic pump200may be supplied to the boom cylinder through the boom control spool310.

The control unit may include a bypass valve610which is provided in the control lines between the manipulation portion52and the main control valve300to block the control pressure (pilot pressure) from being transferred to the main control valve300. The bypass valve610may include an opening/closing valve.

In this case, the control unit may include a fifth control valve to output a pilot signal pressure corresponding to an applied electrical signal, and the fifth control valve may output the pilot signal pressure to the bypass valve610. The fifth control valve may include an electro proportional pressure reducing valve (EPPRV). The bypass valve502may be switched by the pilot signal pressure outputted from the fifth control valve to open and close the control lines, and thus, the pilot pressure from the manipulation portion52may be selectively blocked from being transferred to the boom control spool310.

As illustrated inFIGS. 2 and 3, in example embodiments, the control unit600may include a determiner620which receives a pressure of the accumulator500detected by a pressure sensor504and determines whether or not the hydraulic pump510fails when the hydraulic oil accumulated in the accumulator500is supplied to the hydraulic pump510.

In particular, the determiner620may include a first calculator622to calculate a volume change of the accumulator from the pressure value of the accumulator500, a second calculator624to calculate a flow rate of the hydraulic motor from number of revolution of the hydraulic motor510, and a comparer626to compare the volume change and the flow rate to determine a failure in the hydraulic motor and output a control signal.

FIG. 4is a graph illustrating a pressure change of the accumulator when the hydraulic oil accumulated in the accumulator is supplied to the hydraulic motor inFIG. 2.

Referring toFIG. 4, when the hydraulic oil is supplied from the accumulator500to the hydraulic motor510, a PV curve may represent that state A(t1) moves state B(t2). That is, the pressure of the accumulator500may be decreased from P1to P2and the volume of a gas portion in the accumulator500may be increased from V1to V2. The pressure P of the accumulator500and the volume V of the gas portion may be represented by following equation (1).
PVn=const  Equation (1)

Here, P is a pressure of the accumulator, V is a volume of a gas portion of the accumulator, and n is polytropic index.

The first calculator622may receive a pressure value of the accumulator500from the pressure sensor504and may calculate the volume of the hydraulic oil discharged from the accumulator500using the equation (1).

The hydraulic oil discharged from the accumulator500may be supplied to the hydraulic motor510to generate torque and then may be drained to a drain tank T. The hydraulic motor510may be a variable displacement hydraulic motor. Accordingly, a swash plate angle of the hydraulic motor510may be controlled and an output torque of the hydraulic motor510may be controlled.

The second calculator624may calculate a flow rate of the hydraulic oil discharged through the hydraulic motor510. The flow rate Q of the hydraulic oil flowing through the hydraulic motor510may be represented by following equation (2).

Here, Qmotor_ideal is a flow rate of the hydraulic motor, ωmotor is number of revolution of the hydraulic motor, θmax is a maximum volume of the hydraulic motor, θcmd_current is a current command value of the swash plate of the hydraulic motor, and θcmd_max is a maximum command value of the swash plate of the hydraulic motor.

Because the hydraulic motor510is connected to the drive axis of the engine100through the power take off (PTO) having a predetermined gear ratio, the number of revolution of the hydraulic motor may be represented by following equation (3).
wmotor=wengine×GEquation (3)

Here, wmotor is number of revolution of the hydraulic motor, wengine is engine rpm, G is PTO gear ratio.

The second calculator624may receive engine rpm information from an engine ECU to calculate the number of revolution of the hydraulic motor510using the equation (3) and may calculate the flow rate Q of the hydraulic oil flowing through the hydraulic motor510.

The comparer626may receive and compare the volume value of the hydraulic oil discharged from the accumulator and the flow rate value of the hydraulic oil flowing through the hydraulic motor to determine whether or not the hydraulic motor fails and output a control signal.

When the hydraulic motor510operates normally, the calculated volume change of the accumulator and the calculated flow rate of the hydraulic motor may be identical to each other. When the hydraulic motor510operates abnormally, the calculated volume change of the accumulator and the calculated flow rate of the hydraulic motor may not be identical to each other. Accordingly, the volume change due to the pressure change in the accumulator and the theoretical flow rate value of the hydraulic motor may be calculated to determine whether or not the hydraulic motor fails.

When it is determined that the hydraulic motor fails, the comparer626may output a control signal such that the hydraulic oil discharged from the boom cylinder72may be blocked from being supplied to the regeneration device through the hydraulic regeneration line230and the pilot oil from the manipulation portion52may be supplied to the main control valve300.

In particular, when it is determined that the hydraulic motor fails, if an operator inputs a boom down signal through the manipulation portion52, the control unit may close the hydraulic regeneration line230to block the hydraulic oil from being supplied to the regeneration device through the hydraulic regeneration line230. Additionally, the control unit may open the bypass valve610such that the pilot pressure from the manipulation portion52may be transferred to the boom control spool310of the main control valve300.

Accordingly, the hydraulic oil from the boom head chamber72aof the boom cylinder72may be supplied to the boom control spool310of the main control valve300. The hydraulic oil discharged from the boom cylinder72may be drained to the drain tank T through the main control valve300. On the other hand, the hydraulic regeneration line230may be closed such that the hydraulic oil from the boom head chamber72amay not be supplied to the regeneration device.

When it is determined that the hydraulic motor operates normally, the comparer626may output a control signal such that the hydraulic oil discharged from the boom cylinder72may be supplied to the regeneration device through the hydraulic regeneration line230and the pilot oil from the manipulation portion52may be blocked from being supplied to the main control valve300.

In particular, when it is determined that the hydraulic motor does not fail, if an operator inputs a boom down signal through the manipulation portion52, the control unit may apply a pilot signal pressure to the discharge amount control valve410, the check valve420and the opening/closing valve430to open the hydraulic regeneration line230. Additionally, the control unit may apply a pilot signal pressure to the bypass valve610such that the pilot pressure from the manipulation portion52may be blocked from being applied to the boom control spool310of the main control valve300.

Accordingly, the hydraulic oil from the boom head chamber72aof the boom cylinder72may be supplied to the regeneration device through the hydraulic regeneration line230to regenerate potential energy of the boom. On the other hand, the pilot pressure from the manipulation portion52may not be supplied to the boom control spool310of the main control valve300by the bypass valve610, and accordingly, the boom control spool310may not be switched by the boom down signal and the hydraulic oil discharged from the boom head chamber72amay not be discharged through the boom head hydraulic line222. Thus, the hydraulic oil discharged from the boom cylinder72may be drained to the drain tank T through the hydraulic motor510of the regeneration device.

As mentioned above, the hydraulic control apparatus of construction machinery may calculate the volume change due to the pressure change in the accumulator500and the theoretical flow rate value of the hydraulic motor510to determine whether or not the hydraulic motor510fails.

Accordingly, because an extra swash plate sensor for detecting a failure in the hydraulic motor is not needed, a design modification of the hydraulic motor may not be required, and whether or not the hydraulic motor fails may be determined using the above software calculation. When it is determined that the hydraulic motor fails, the boom energy regeneration device may discontinue to operate and an operator may be informed of an alarm signal in order for rapid repairs.

FIG. 5is a hydraulic circuit diagram illustrating a hydraulic system for construction machinery in accordance with example embodiments. The hydraulic system for construction machinery may be substantially the same as or similar to the hydraulic system for construction machinery as described with reference toFIGS. 1 to 3, except that the hydraulic system includes an electro-hydraulic control valve. Thus, same reference numerals will be used to refer to the same or like elements and any further repetitive explanation concerning the above elements will be omitted.

Referring toFIG. 5, in example embodiments, a main control valve300may include an electro-hydraulic control valve. A boom control spool310may be controlled by an electro proportional pressure reducing valve (EPPRV) which outputs a secondary pressure (pilot pressure) in proportion to an external pressure command signal (control current signal).

In particular, a control unit may receive an electrical signal in proportion to a manipulation amount of an operator from a manipulation portion52, and may output the pressure command signal (control current signal) to the electro proportional pressure reducing valves312corresponding to the electrical signal. The electro proportional pressure reducing valves312may output the secondary pressure in proportion to the pressure command signal to the boom control spool310to control the boom control spool with the electrical signal.

A pair of the electro proportional pressure reducing valves312may be provided in both sides of the boom control spool310. The electro proportional pressure reducing valve may supply a secondary pressure in proportion to the pressure command signal to the boom control spool such that the boom control spool may be displaced in proportion to the secondary pressure. Thus, a hydraulic oil from a hydraulic pump200may be supplied to a boom cylinder72through the boom control spool310.

The control unit may include a controller to apply a pressure command signal (for example, control current signal) as an electrical signal to the electro proportional pressure reducing valves312of the main control valve300. The controller may selectively apply the pressure command signal corresponding to the electrical signal applied from the manipulation portion52, to the electro proportional pressure reducing valves312of the main control valve300. For example, the controller may not apply the pressure command signal to the electro proportional pressure reducing valves312, such that a control pressure (pilot pressure) from the manipulation portion52may be blocked from being transferred to the main control valve300.

When it is determined that a hydraulic pump fails, a comparer626may output a control signal such that the hydraulic oil discharged from the boom cylinder72may be blocked from being supplied to a regeneration device through a hydraulic regeneration line230and the pilot pressure from the manipulation portion52may be supplied to the main control valve300.

In particular, when it is determined that the hydraulic motor fails, if an operator inputs a boom down signal through the manipulation portion52, the control unit may close the hydraulic regeneration line230to block the hydraulic oil from being supplied to the regeneration device through the hydraulic regeneration line230. Additionally, the control unit may apply the pressure command signal to the electro proportional pressure reducing valves312such that the pilot pressure from the manipulation portion52may be transferred to the boom control spool310of the main control valve300.

Accordingly, the hydraulic oil from the boom head chamber72aof the boom cylinder72may be supplied to the boom control spool310of the main control valve300. The hydraulic oil discharged from the boom cylinder72may be drained to the drain tank T through the main control valve300. On the other hand, the hydraulic regeneration line230may be closed such that the hydraulic oil from the boom head chamber72amay not be supplied to the regeneration device.

When it is determined that the hydraulic motor operates normally, the comparer626may output a control signal such that the hydraulic oil discharged from the boom cylinder72may be supplied to the regeneration device through the hydraulic regeneration line230and the pilot oil from the manipulation portion52may be blocked from being supplied to the main control valve300.

In particular, when it is determined that the hydraulic motor does not fail, if an operator inputs a boom down signal through the manipulation portion52, the control unit may apply a pilot signal pressure to a discharge amount control valve410, a check valve420and a opening/closing valve430to open the hydraulic regeneration line230. Additionally, the control unit may not apply the pressure command signal to the electro proportional pressure reducing valves312such that the pilot pressure from the manipulation portion52may be blocked from being applied to the boom control spool310of the main control valve300.

Accordingly, the hydraulic oil from the boom head chamber72aof the boom cylinder72may be supplied to the regeneration device through the hydraulic regeneration line230to regenerate potential energy of the boom. On the other hand, the boom control spool310of the main control valve300may not be switched such that the hydraulic oil discharged from the boom head chamber72amay not be discharged through the boom head hydraulic line222. In the boom down regeneration mode, the hydraulic oil may be drained to the drain tank T through the hydraulic motor of the regeneration device.

Hereinafter, a hydraulic control method for construction machinery using the hydraulic system inFIGS. 2 and 5will be explained.

FIG. 6is a flow chart illustrating a hydraulic control method of construction machinery in accordance with example embodiments.

Referring toFIGS. 2, 5 and 6, first, a hydraulic oil discharged from a boom cylinder72of construction machinery may be accumulated in an accumulator500, and then, the hydraulic oil accumulated in the accumulator500may be supplied to a hydraulic motor510.

In example embodiments, a regeneration device including the accumulator500and the hydraulic motor510may regenerate energy using the high-pressure hydraulic oil discharged from a boom head chamber72aof the boom cylinder72when a boom70is lowered.

The accumulator500may accumulate the high-pressure hydraulic oil which is discharged from the boom head chamber72aof the boom cylinder72when the boom is lowered. The hydraulic motor510may be connected to the accumulator500. The hydraulic motor510may be driven by the hydraulic oil accumulated in the accumulator500. The hydraulic motor510may be connected to a drive axis of an engine100to assist an output power of the engine, thereby providing a rotational force to a hydraulic pump200,202.

When the hydraulic oil accumulated in the accumulator500is supplied to the hydraulic motor510, a pressure of the accumulator500may be detected to calculate a volume change of the accumulator500and number of revolution of the hydraulic motor510may be detected to calculate a flow rate of the hydraulic oil flowing through the hydraulic motor510(S100, S110).

In example embodiments, a first calculator622may receive a pressure value of the accumulator500from a pressure sensor504and may calculate the volume of the hydraulic oil discharged from the accumulator500. A second calculator624may receive engine rpm information from an engine ECU to calculate the number of revolution of the hydraulic motor510and may calculate the flow rate of the hydraulic oil flowing through the hydraulic motor510.

Then, the volume value of the hydraulic oil discharged from the accumulator and the flow rate value of the hydraulic oil flowing through the hydraulic motor may be compared to determine whether or not the hydraulic motor510fails and an operation of the regeneration device may be controlled (S120, S130).

When the hydraulic pump510operates normally, the calculated volume change of the accumulator and the calculated flow rate of the hydraulic motor may be identical to each other. When the hydraulic motor510operates abnormally, the calculated volume change of the accumulator and the calculated flow rate of the hydraulic motor may not be identical to each other. Accordingly, the calculated volume change due to the pressure change in the accumulator and the theoretical flow rate value of the hydraulic motor may be calculated to determine whether or not the hydraulic motor fails.

When it is determined that the hydraulic motor fails, the hydraulic oil discharged from the boom cylinder72may be blocked from being supplied to the regeneration device through a hydraulic regeneration line230and a pilot oil from a manipulation portion52may be supplied to a main control valve300.

Accordingly, the hydraulic oil from a boom head chamber72aof the boom cylinder72may be supplied to a boom control spool310of the main control valve300. The hydraulic oil discharged from the boom cylinder72may be drained to the drain tank T through the main control valve300. On the other hand, the hydraulic regeneration line230may be closed such that the hydraulic oil from the boom head chamber72amay not be supplied to the regeneration device.

When it is determined that the hydraulic motor operates normally, the hydraulic oil discharged from the boom cylinder72may be supplied to the regeneration device through the hydraulic regeneration line230and the pilot oil from the manipulation portion52may be blocked from being supplied to the main control valve300.

Accordingly, the hydraulic oil from the boom head chamber72aof the boom cylinder72may be supplied to the regeneration device through the hydraulic regeneration line230to regenerate potential energy of the boom.

The present invention has been explained with reference to preferable embodiments, however, those skilled in the art may understand that the present invention may be modified or changed without being deviated from the concept and the scope of the present invention disclosed in the following claims.

THE DESCRIPTION OF THE REFERENCE NUMERALS