Boom driving system for hybrid excavator and control method therefor

Abstract

The present disclosure relates to a boom driving system for a hybrid excavator and a control method therefor, and more particularly, to a boom driving system for a hybrid excavator, which drives a hydraulic pump motor so as to move a boom upward and downward, and collects regenerative power of the boom using an electric motor so as to improve fuel efficiency, and a control method for the boom driving system. Provided in exemplary embodiments of the present disclosure is a boom driving system for a hybrid excavator and a control method therefor, which may allow an electric motor generator to normally produce electricity by allowing retraction speed and force of the boom actuator to be controlled to a target speed when a boom is moved downward.

Claims

1. A boom driving system for a hybrid excavator, comprising: an electric motor which is operated as a motor or a generator; an electric energy storage device which stores electricity produced by the electric motor; a hydraulic pump motor which is operated by the electric motor and supplies a hydraulic fluid to a boom actuator; a boom control valve which configures a closed circuit so as to selectively connect or disconnect a discharge line of the hydraulic pump motor and an inlet line of the hydraulic pump motor to/from a head side or a rod side of a boom cylinder that operates the boom actuator; a first control valve which connects the inlet line to a drain tank; a second control valve which connects the discharge line to the drain tank, and of which the opening area is controlled to be changed according to a size of torque that is applied to the electric motor when the boom actuator performs a downward operation; and a control unit which controls the electric motor, the hydraulic pump motor, the boom control valve, and the first and second control valves, wherein the control unit determines whether operating torque of the electric motor has a plus value or a minus value, and controls the second control valve to be maximally opened when the operating torque has the minus value and controls the opening area of the second control valve to be reduced when the operating torque has the plus value.

2. The boom driving system of claim 1, wherein the first control valve is connected when the boom actuator performs an upward operation, and shut off when the boom actuator performs the downward operation, and the second control valve is shut off when the boom actuator performs the upward operation, and connected when the boom actuator performs the downward operation.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 are views for explaining a boom driving system for a hybrid excavator in the related art.

(2) FIGS. 3 and 4 are views for explaining a boom driving system for a hybrid excavator and a control method therefor according to an exemplary embodiment of the present disclosure, and for explaining a regenerative downward movement of a boom and a load downward movement of the boom when the boom is moved downward.

(3) FIG. 5 is graphs for explaining characteristics of the boom driving system for a hybrid excavator according to the exemplary embodiment of the present disclosure.

(4) FIG. 6 is a flowchart for explaining the boom driving system for a hybrid excavator and the control method therefor according to the exemplary embodiment of the present disclosure.

DESCRIPTION OF MAIN REFERENCE NUMERALS OF DRAWINGS

(5) 100: Boom actuator 110: Electronic device (electric motor, electric energy storage device, inverter, etc.) 120: Hydraulic pump motor 121: Discharge line 122: Inlet line 125: Boom control valve 126, 127, 128: First, second, and third positions 144: Boom auxiliary valve 145: Boom auxiliary line 151, 152: First and second control valves 160: Control unit 200: Motor bypass valve 300: Second control valve 301: Completely opened position 302: Opening area reducing position 303: Completely closed position

DETAILED DESCRIPTION

(6) Advantages and features of some embodiments of the present disclosure and methods of achieving some or all of the advantages and features will be clear with reference to an exemplary embodiment described in detail below together with the accompanying drawings.

(7) Like reference numerals indicate like elements throughout the specification, constituent elements identical to constitute elements in the related art will be indicated by the same reference numerals, and duplicated detailed descriptions thereof will be omitted.

(8) Meanwhile, the terms used in the description are defined considering the functions of the present disclosure and may vary depending on the intention or usual practice of a manufacturer. Therefore, the definitions should be made based on the entire contents of the present specification.

(9) Hereinafter, a boom driving system for a hybrid excavator and a control method therefor according to an exemplary embodiment of the present disclosure will be described with reference to FIGS. 3 to 6.

(10) The attached FIGS. 3 and 4 are views for explaining the boom driving system for a hybrid excavator and the control method therefor according to the exemplary embodiment of the present disclosure, and for explaining a regenerative downward movement of a boom and a load downward movement of the boom when the boom is moved downward. The attached FIG. 5 shows graphs for explaining characteristics of the boom driving system for a hybrid excavator according to the exemplary embodiment of the present disclosure. The attached FIG. 6 is a flowchart for explaining the boom driving system for a hybrid excavator and the control method therefor according to the exemplary embodiment of the present disclosure.

(11) The boom driving system for a hybrid excavator according to the exemplary embodiment of the present disclosure is configured by coupling an electronic device and a hydraulic device.

(12) The electronic device includes an electric motor, an electric energy storage device 115, an inverter, and the like. The electric motor is operated as a motor or a generator. The inverter stabilizes an operation of the electric motor. The electric energy storage device 115 stores electricity produced by an electric motor.

(13) The hydraulic device includes a boom actuator 100, a hydraulic pump motor 120, and a boom control valve 125.

(14) The hydraulic pump motor 120 may serve as both a hydraulic pump and a hydraulic motor. When the hydraulic pump motor 120 is operated as a hydraulic pump, the hydraulic pump motor 120 is operated by the electric motor so as to supply a hydraulic fluid to the boom actuator 100. When the hydraulic pump motor 120 is operated as a hydraulic motor, the hydraulic pump motor 120 is operated by the hydraulic fluid discharged from the boom actuator 100 so as to operate the electric motor.

(15) A discharge line 121 and an inlet line 122 are connected to one side of the hydraulic pump motor 120. The other side of the discharge line 121 and the other side of the inlet line 122 are connected to the boom control valve 125.

(16) The boom control valve 125 may be connected in a forward direction in order to allow the boom actuator 100 to perform an upward operation, may be connected in a reverse direction in order to allow the boom actuator 100 to perform a downward operation, and may have a neutral position so as to stop the upward and downward operations of the boom actuator 100.

(17) On the other hand, one side of a boom auxiliary line 145 may be connected to the discharge line 121, and a boom auxiliary valve 144 may be provided at the other side of the boom auxiliary line 145. The boom auxiliary valve 144 is controlled to add and supply the hydraulic fluid from a main hydraulic pump to the discharge line 121.

(18) On the other hand, the boom driving system for a hybrid excavator according to the exemplary embodiment of the present disclosure may further include a first control valve 151 which connects the inlet line 122, which connects the hydraulic pump motor 120 and the boom control valve 125, to a drain tank for draining the hydraulic fluid. In addition, the boom driving system may further include a second control valve 300 which connects the discharge line 121, which connects the hydraulic pump motor 120 and the boom control valve 125, to the drain tank for draining the hydraulic fluid.

(19) A control unit 160 controls the first control valve 151 and a second control valve 300.

(20) In more detail, the first control valve 151 is connected when the boom actuator 100 performs the upward operation, and shut off when the boom actuator 100 performs the downward operation.

(21) The second control valve 300 is shut off when the boom actuator 100 performs the upward operation, and connected when the boom actuator 100 performs the downward operation.

(22) In addition, the second control valve 300 may be provided as a three-position and two-port type. A first position may be a completely opened position 301, a second position may be an opening area reducing position 302, and a third position may be a completely closed position 303.

(23) Here, an opening area of the second control valve 300 through which the hydraulic fluid passes is changed according to a position of a spool.

(24) Meanwhile, in a case in which a required flow rate, which corresponds to a signal of an upward movement of the boom, exceeds a supply flow rate of the hydraulic pump motor 120, or exceeds a capacity of the electric motor 110, the boom auxiliary valve 144 may be controlled to be opened so that the hydraulic fluid discharged from a first hydraulic pump 141 is supplied to the boom actuator 100.

(25) In addition, in a case in which a flow rate of hydraulic fluid, which flows from the boom actuator 100 into the hydraulic pump motor 120, exceeds a permissible flow rate of the hydraulic pump motor 120, or exceeds a power generation capacity of the electric motor 110 when the boom actuator 100 performs the downward operation, the first control valve 151 may be connected to the tank and may discharge a surplus amount of hydraulic fluid to the tank.

(26) Hereinafter, the control method for the boom driving system for a hybrid excavator according to the exemplary embodiment of the present disclosure will be described with reference to the attached FIGS. 5 and 6.

(27) First detecting step S10: a value of boom downward movement joystick pressure is detected.

(28) Second detecting step S20: operating torque of the boom electric motor is detected.

(29) Determining step S30: whether the operating torque detected in the second detecting step S20 has a plus (+) value or a minus (−) value is determined.

(30) First performing step S40: when the operating torque has a minus (−) value in the determining step S30, the second control valve 300 is maximally opened. That is, a position of the second control valve 300 is controlled to the completely opened position 301.

(31) Second performing step S50: when the operating torque has a plus (+) value in the determining step S30, the opening area of the second control valve 300 is controlled to be reduced. That is, the opening area is controlled to be smaller than the maximum opening area.

(32) In the exemplary embodiment of the present disclosure, as a reference for determining a regenerative downward movement or a load downward movement, a value of the operating torque, which is applied to the electric motor, is determined. In more detail, the regenerative downward movement is determined when the operating torque has a minus (−) value, and the load downward movement is determined when the operating torque has a plus (+) value. Here, the operating torque is torque of the electric motor which is controlled to rotate the electric motor at a target rotational speed.

(33) When the load downward movement of the boom is performed, the second control valve 300 is controlled such that pressure in the discharge line 121, which is connected with the cylinder rod of the boom actuator, is controlled when the boom is moved downward.

(34) When the load downward movement of the boom is performed, a position of the second control valve 300 is controlled to the opening area reducing position 302, such that a flow path connected to the drain tank may be reduced, and as a result, pressure in the discharge line 121 is increased. The pressure, which is increased as described above, is transmitted to the cylinder rod side of the boom actuator 100, and as a result, a speed at which the boom actuator 100 is retracted may be controlled to a desired speed.

(35) Hereinafter, an operation of the second control valve 300 will be described with reference to the graphs illustrated in FIG. 5.

(36) When the regenerative downward movement of the boom is performed, the second control valve 300 is maximally opened. The boom electric motor is operated by the hydraulic pump motor 120 that is operated as a hydraulic motor by pressurized oil that is supplied through the inlet line 122 from a cylinder head of the boom actuator 100. In this case, pressure of a joystick 161 is defined by p1, and a rotational speed of the electric motor is defined by w1.

(37) In this case, an external load, which is applied to the boom actuator 100, is f1, and torque, which is finally transmitted to the boom electric motor, is T1. The boom electric motor regenerates power by w1×T1. In this case, the second control valve 300 is maximally opened, as illustrated in FIG. 5C.

(38) Meanwhile, as external force is applied to a bucket, a regenerable load may be decreased from f1 to f2. In this case, torque, which is transmitted to the boom electric motor, is decreased from T1 to T2. However, even in this case, the boom electric motor regenerates power by T2. Similarly, the second control valve 300 is maximally opened, as illustrated in FIG. 5C.

(39) On the other hand, when a larger amount of external force is applied to the bucket, pressure in the inlet line 122 may not rotate the boom electric motor at a target rotational speed illustrated in FIG. 5A. The boom electric motor is rotated using electric power from the electric energy storage device 115, and in this case, an external load is defined by f3, and torque of the electric motor is defined by T3.

(40) In this case, when torque of the boom electric motor is changed from a minus (−) value to a plus (+) value, the control unit 160 controls the second control valve 300 so that the opening area thereof through which a fluid will pass is decreased to a3. If required torque of the electric motor becomes larger as an external load becomes greater than f3, the second control valve 300 is finally closed such that the overall hydraulic fluid discharged by the hydraulic pump motor is transmitted to the rod side of the boom actuator 100, thereby increasing downward force when the boom is moved downward.

(41) When the opening area of the second control valve 300 connected to the drain tank is decreased, pressure in a flow path of the discharge line 121 is increased. This pressure is transmitted to the rod side of the boom cylinder of the boom actuator 100 so as to control the boom cylinder at a desired speed.

(42) According to the boom driving system for a hybrid excavator and the control method therefor according to the exemplary embodiment of the present disclosure, which are configured as described above, a retraction speed of the boom actuator may be controlled to a target speed when the boom is moved downward, thereby allowing an electric motor generator to normally produce electricity.

(43) The exemplary embodiments of the present disclosure have been described with reference to the accompanying drawings, but those skilled in the art will understand that the present disclosure may be implemented in any other specific form without changing the technical spirit or an essential feature thereof.

(44) Accordingly, it should be understood that the aforementioned exemplary embodiment is described for illustration in all aspects and are not limited, and the scope of the present disclosure shall be represented by the claims to be described below, and it should be construed that all of the changes or modified forms induced from the meaning and the scope of the claims, and an equivalent concept thereto are included in the scope of the present disclosure.

(45) The boom driving system for a hybrid excavator and the control method therefor according to the present disclosure may be used to move the boom upward, and collect regenerative energy when the boom is moved downward.