Patent Description:
Construction equipment, for example, an excavator generates large force using hydraulic pressure. The force enables a work unit of the excavator to excavate earth and sand/solid rock or dump excavated earth and sand/solid rock.

In order to use this hydraulic pressure, a hydraulic pump pumps up oil stored in an oil tank and supplies the oil as a pressurized oil to an actuator that actuates the work unit. An engine needs to be operated to drive the hydraulic pump and fuel needs to be consumed to operate the engine.

Energy recuperation technology has been used to increase fuel efficiency of construction equipment by reducing fuel consumption. The energy recuperation technology has a mechanism that charges an accumulator with a pressurized oil, which has been supplied to the actuator while the work unit freely drops, without discharging the pressurized oil to the oil tank and then supplies the charged oil to another hydraulic component. According to its abstract, <CIT> relates to a hydraulic circuit capable of saving a pump flow rate while hydraulic fluid is being accumulated in an accumulator. Further, <CIT> relates to a work vehicle having a hydrostatic drive system which provides for the recovery and reuse of the vehicle's kinetic energy by conducting pressurized hydraulic fluid out of the hydrostatic drive system into an accumulator during vehicle deceleration, and conducting the pressurized fluid back into the drive system during vehicle acceleration to assist the vehicle's engine in accelerating the vehicle.

According to the energy recuperation technology, an energy recuperation ratio may be low, depending on a pressure condition of the accumulator, or in order to increase an energy recuperation ratio, the response speed of an excavator may be reduced. Accordingly, energy is not efficiently recuperated.

An object of the present invention is to provide energy recuperation system and method for construction equipment, the system and method being able to improve energy recuperation efficiency by maintaining a dischargeable lowest limit pressure of an accumulator at an optimum level in energy recuperation while construction equipment is in operation.

Another object of the present invention is to provide energy recuperation system and method for construction equipment, the system and method being able to increase not only a response speed of construction equipment, but also energy recuperation efficiency.

According to an exemplary embodiment of the present invention, there is provided an energy recuperation system for construction equipment including: an actuator driving upward and downward operations of a work unit; an accumulator connected to the actuator; and a controller determining a predicted downward mode associated with the downward operation of the work unit, regulating a dischargeable lowest limit pressure of the accumulator to a target pressure corresponding to the predicted downward mode, and charging the accumulator having the dischargeable lowest limit pressure regulated to the target pressure with pressurized oil discharged from the actuator during the downward operation of the work unit to recuperate energy.

The system may further include: a memory configured to store information associated with the predicted downward mode and the target pressure, and to be controlled by the controller, in which the predicted downward mode may include: a first predicted downward mode where the work unit has a first downward acceleration force at the downward operation; and a second predicted downward mode where the work unit has a second downward acceleration force at the downward operation, the second downward acceleration force being less than the first downward acceleration force, in which the target pressure may include: a first target pressure; and a second target pressure having a higher pressure level than the first target pressure, in which the controller may be configured to correspond the first predicted downward mode with the first target pressure, and to correspond the second predicted downward mode with the second target pressure.

The system may further include: a hydraulic pump configured to supply pressurized oil to the actuator; an assist motor configured to assist an engine to drive the hydraulic pump; an assist passage connecting the accumulator and the assist motor to each other; and an assist valve disposed in the assist passage and configured to control supply of the pressurized oil charged in the accumulator to the assist motor through the assist passage, in which the controller may control opening/closing of the assist valve so that the dischargeable lowest limit pressure of the accumulator reaches the first target pressure or the second target pressure.

The accumulator may include a plurality of sub-accumulators having different initial pressures, and the controller may charge a sub-accumulator, which has an initial pressure corresponding to the target pressure, of the sub-accumulators with the pressurized oil.

The system may further include: a charge passage connecting the accumulator and the actuator to each other; and a charge valve disposed in the charge passage, in which the controller may regulate pressure of the pressurized oil to be supplied into the accumulator by controlling the charge valve.

The system may further include a motion sensor configured to measure information about one of upward and downward operations of the work unit, in which the controller may acquire upward/downward operation pattern information by analyzing information measured by the motion sensor and may determine the predicted downward mode on the basis of the upward/downward operation pattern information.

The system may further include: a lower driving structure; an upper swing structure on which the work unit is mounted; and a swing module connecting the upper swing structure rotatably to the lower driving structure, in which the controller may additionally charge the accumulator, which has been charged with the pressurized oil during downward of the work unit under the second target pressure, with pressurized oil discharged from the swing module while the swing module stops a swing operation.

According to another exemplary embodiment of the present invention, there is provided an energy recuperation method for construction equipment including: determining a predicted downward mode of a work unit; regulating a dischargeable lowest limit pressure of an accumulator to a target pressure on the basis of the predicted downward mode; and charging the accumulator having the dischargeable lowest limit pressure regulated to the target pressure with pressurized oil discharged from the actuator actuating the work unit during downward of the work unit to recuperate energy.

The determining of the predicted downward mode of the work unit may further include: referring to a memory storing information about the predicted downward mode and the target pressure wherein the predicted downward mode includes a first predicted downward mode and a second predicted downward mode and the target pressure includes a first target pressure and a second target pressure having a higher pressure level than the first target pressure, and the regulating of the dischargeable lowest limit pressure of the accumulator to the target pressure on the basis of the predicted downward mode may include setting the dischargeable lowest limit pressure to the first target pressure to correspond to the first predicted downward mode, or setting the dischargeable lowest limit pressure to the second target pressure to correspond to the second predicted downward mode.

The regulating of the dischargeable lowest limit pressure of the accumulator to the target pressure on the basis of the predicted downward mode may include regulating opening/closing of an assist valve such that the dischargeable lowest limit pressure reaches the first target pressure or the second target pressure while the pressurized oil charged in the accumulator is discharged to an assist motor.

The accumulator may include a plurality of sub-accumulators having different initial pressures, and the regulating of the dischargeable lowest limit pressure of the accumulator to the target pressure on the basis of the predicted downward mode may include selecting a sub-accumulator having an initial pressure corresponding to the first target pressure or the second target pressure from the sub-accumulators as an object to be charged with the pressurized oil discharged from the actuator.

The selecting of the sub-accumulator having the initial pressure corresponding to the first target pressure or the second target pressure from the sub-accumulators as an object to be charged with the pressurized oil discharged from the actuator may include making some of the sub-accumulators be objects to be charged with pressurized oil by selectively opening/closing selection valves disposed for the sub-accumulators, respectively.

The accumulator may include a plurality of sub-accumulators having different initial pressures, and the charging of the accumulator having the dischargeable lowest limit pressure regulated to the target pressure with pressurized oil discharged from the actuator actuating the work unit during downward of the work unit to recuperate energy may include sequentially charging the sub-accumulators with the pressurized oil discharged from the actuator such that the dischargeable lowest limit pressure of the accumulator reaches the first target pressure and the second target pressure with an interval.

The determining of the predicted downward mode may include selecting one of the first predicted downward mode and the second predicted downward mode as the predicted downward mode on the basis of work input from an operator through a work selector.

The first predicted downward mode may be a mode where the work unit is turned down with a first downward acceleration force and the second predicted downward mode may be a mode where the work unit is turned down with a second downward acceleration force less than the first downward acceleration force.

The method may further include acquiring upward/downward operation pattern information by analyzing one of upward and downward operations of the work unit, in which the determining of the predicted downward mode of the work unit may include determining the predicted downward mode as one of the first predicted downward mode and the second predicted downward mode on the basis of the upward/downward operation pattern information.

The method may further include acquiring upward/downward operation pattern information by analyzing one of upward and downward operations of the work unit, in which the acquiring of the upward/downward operation pattern information by analyzing one of upward and downward operations of the work unit may include acquiring upward operation pattern information by analyzing upward factor information associated with upward of the work unit.

The upward operation pattern information may include one of a stroke value of the actuator, an operation amount of an operation lever for the actuator, operation time of the operation lever, and an upward acceleration value of the work unit.

The determining of the predicted downward mode of the work unit may include determining the predicted downward mode as the first predicted downward mode if the stroke value is larger than a reference stroke value, or determining the predicted downward mode as the second predicted downward mode if the stroke value is smaller than the reference stroke value.

The method may further include determining a starting time to charge the accumulator on the basis of the upward/downward operation pattern information.

According to the energy recuperation system and method of the present invention, since a dischargeable lowest limit pressure of an accumulator is regulated to a target pressure suitable for a downward operation of a work unit to recuperate energy while construction equipment is in operation, pressurized oil discharged from the work unit can be maximally supplied into the accumulator, so a high energy recuperation ratio can be achieved.

Further, when the accumulator is charged with the pressurized oil, the difference between the pressure of the pressurized oil discharged from the work unit and the dischargeable lowest limit pressure of the accumulator is reduced, so a loss of pressure (a loss of energy) due to the difference can also be reduced.

Further, since the dischargeable lowest limit pressure of the accumulator is regulated, the energy of the pressurized oil discharged from the work unit can be recuperated and the response speed of operations of the work unit can be improved.

Further, since the dischargeable lowest limit pressure of the accumulator is regulated by combining different initial pressures of a plurality of sub-accumulators, it is possible to provide various designs to the accumulator in terms of energy recuperation and response speed.

Hereinafter, energy recuperation system and method for construction equipment according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. The same and like reference numerals are used for the same and like components herein even in different embodiments and the latter description refers to the earlier description.

<FIG> is a perspective view showing construction equipment <NUM> having an energy recuperation system for construction equipment according to an embodiment of the present invention.

Referring to the figure, the construction equipment <NUM> will be described by exemplifying an excavator. The excavator is given reference number '<NUM>' hereafter, the same as the construction equipment <NUM>. However, the construction equipment <NUM> is not limited to an excavator. The construction equipment <NUM> may include a back-hoe and a dragline as long as they have a work unit that is hydraulically turned up and down such as a boom or an arm.

The excavator <NUM> may include a lower driving structure <NUM>, an upper swing structure <NUM>, work units <NUM>, <NUM>, and <NUM>, actuators <NUM>, <NUM>, and <NUM>, and a swing module <NUM>.

The lower driving structure <NUM> is disposed at a lower portion in the excavator <NUM> and is in charge of moving the excavator <NUM>. The lower driving structure <NUM>, in detail, includes a frame <NUM> and crawlers <NUM>. The frame <NUM> has a substantially rectangular top. The crawlers <NUM> are coupled to both sides of the frame <NUM> and protrude up further than the frame <NUM>. The crawlers <NUM> are rotated by power from an engine or an electric motor so that the excavator <NUM> can move. Unlike the crawler excavator, wheels and covers that cover the wheels may be employed instead of the crawlers <NUM> in a wheel excavator.

The upper swing structure <NUM> is disposed at an upper portion in the excavator <NUM> and is in direct charge of work by the excavator <NUM>. To this end, the boom <NUM> of the work units <NUM>, <NUM>, and <NUM> is rotatably mounted on the upper swing structure <NUM>. Further, the upper swing structure <NUM> may have a cab <NUM> and a machine room <NUM>. An operator controls the work units <NUM>, <NUM>, and <NUM> by operating an operation lever <NUM> (see <FIG>) in the cab <NUM>. Hydraulic machines such as a hydraulic pump <NUM> (see <FIG>) are disposed in the machine room <NUM> and drive the actuators <NUM>, <NUM>, and <NUM> using hydraulic power.

The work units <NUM>, <NUM>, and <NUM> are components that directly perform various works on earth and sand, or solid rocks, for example, digging and grading, using hydraulic power. The work units <NUM>, <NUM>, and <NUM>, in detail, may include a boom <NUM>, an arm <NUM>, and a bucket <NUM>. The boom <NUM> is rotatably connected to the upper swing structure <NUM> and the free end of the boom <NUM> can be moved along an arc-shaped path. The arm <NUM> is also rotatably connected to the free end of the boom <NUM>. The arm <NUM> may be shorter than the boom <NUM>. The bucket <NUM> is rotatably connected to the free end of the arm <NUM> and has a structure that can load earth and sand therein. Instead of the bucket <NUM>, a ripper or a crusher may be coupled to the arm <NUM>.

The actuators <NUM>, <NUM>, and <NUM> actuate the work units <NUM>, <NUM>, and <NUM> by supplying hydraulic power to the work units <NUM>, <NUM>, and <NUM>. The actuators <NUM>, <NUM>, and <NUM>, in detail, may include a boom cylinder <NUM>, an arm cylinder <NUM>, and a bucket cylinder <NUM>. The boom cylinder <NUM> connects the upper swing structure <NUM> and the arm cylinder <NUM> to turn up and down the boom <NUM> by stretching and contracting. The arm cylinder <NUM> connects the boom <NUM> and the arm <NUM> to each other to turn up and down the arm <NUM>. Similarly, the bucket cylinder <NUM> connects the bucket <NUM> and the arm <NUM> to each other to turn up and down the bucket <NUM>.

The swing module <NUM> connects the lower driving structure <NUM> and the upper swing structure <NUM> to each other. Further, the swing module <NUM> includes parts such as a swing bearing that enables the upper swing structure <NUM> to swing with respect the lower driving structure <NUM> and a swing motor that generates hydraulic force for a swing operation.

The energy recuperation system and method according to the present invention are described with a focus on the boom <NUM> of the work units <NUM>, <NUM>, and <NUM>. Accordingly, the actuators <NUM>, <NUM>, and <NUM> are described with a focus on the boom cylinder <NUM> associated with the boom <NUM>. Even though described with a focus on the boom <NUM> and the boom cylinder <NUM>, the energy recuperation system and method can be equivalently applied to the arm <NUM> and the arm cylinder <NUM>, etc..

<FIG> is a conceptual view showing the main configuration of the energy recuperation system for construction equipment shown in <FIG>.

Referring to <FIG>, the energy recuperation system may include a pressurized oil production module, a pressurized oil guide module, a pressurized flow control module, and a pressurized oil storage module.

The pressurized oil production module produces a pressurized oil at high pressure, for example, a pressurized oil having pressure required for the boom cylinder <NUM> from oil at the atmospheric pressure. The pressurized oil production module may include an engine <NUM>, a hydraulic pump <NUM>, an assist motor <NUM>, and an oil tank <NUM>. The engine <NUM> generates mechanical torque by burning fuel such as diesel. The hydraulic pump <NUM> is rotated by the torque from the engine <NUM>, thereby pumping the oil in the oil tank <NUM> as the pressurized oil. The assist motor <NUM> is disposed between the engine <NUM> and the hydraulic pump <NUM> and assists the engine <NUM> to rotate the hydraulic pump <NUM>. The assist motor <NUM> is a hydraulic motor that is operated by hydraulic pressure.

The pressurized oil guide module has passages for guiding the pressurized oil discharged from the hydraulic pump <NUM> to the boom cylinder <NUM>, the assist motor <NUM>, the oil tank <NUM>, or an accumulator <NUM>. The passages, in detail, may include an output passage <NUM>, a supply passage A <NUM>, a supply passage B <NUM>, an assist passage <NUM>, and a charge passage <NUM>. The output passage <NUM> means a passage through which the pressurized oil is discharged from the hydraulic pump <NUM>. The supply passage A <NUM> is connected to the output passage <NUM> and to a chamber A 41a of the boom cylinder <NUM>. The supply passage B <NUM> is connected to the output passage <NUM> and to a chamber B 41b of the boom cylinder <NUM>. The assist passage <NUM> connects the assist motor <NUM> and the accumulator <NUM> to each other. The charge passage <NUM> connects the supply passage A <NUM> and the accumulator <NUM> to each other. Further, there may be provided a bridge passage <NUM> connecting the supply passage A <NUM> and the supply passage B <NUM> to each other and a return passage <NUM> connecting the supply passage A <NUM> and the supply passage B <NUM> to the oil tank <NUM>.

The pressurized flow control module controls flow of the pressurized oil in the passages by opening/closing the passages. The pressurized flow control module may include a supply valve A <NUM>, a supply valve B <NUM>, a return valve A <NUM>, a return valve <NUM>, a bridge valve <NUM>, an assist valve <NUM>, and a charge valve <NUM>. The supply valve A <NUM> is disposed in the supply passage A <NUM> and controls the pressurized oil that is supplied to the chamber A 41a of the boom cylinder <NUM> through the output passage <NUM> and the supply passage A <NUM>. The supply valve B <NUM> is disposed in the supply passage B <NUM> and controls the pressurized oil that is supplied to the chamber B 41b of the boom cylinder <NUM> through the output passage <NUM> and the supply passage B <NUM>. The return valve A <NUM> and the return valve B <NUM> open/close the passage for returning the pressurized oil from the chamber A 41a/chamber B 41b of the boom cylinder <NUM> to the oil tank <NUM>. The bridge valve <NUM> is disposed in the bridge passage <NUM> and controls the pressurized oil that is supplied from one of the chamber A 41a and the chamber B 41b to the other one. The assist valve <NUM> controls the pressurized oil that is supplied to the assist module <NUM> from the accumulator <NUM>. The charge valve <NUM> is disposed in the charge passage <NUM> and opened/closed so that the pressurized oil discharged from the chamber 41a is supplied into the accumulator <NUM> or stops being supplied.

<FIG> is a control block diagram of the construction equipment <NUM> for illustrating additional components of the energy recuperation system shown in <FIG>.

Referring to this figure, the excavator <NUM>, in addition to the engine <NUM> and valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, may further include a controller <NUM>, a motion sensor <NUM>, a work selector <NUM>, an operation lever <NUM>, and a memory <NUM>.

The controller <NUM> is electrically connected to the engine <NUM>, the valves <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>, the motion sensor <NUM>, and the like, thereby controlling them or receiving information from them. The controller <NUM> controls the assist valve <NUM>, the charge valve <NUM> etc. to recuperate energy from the pressurized oil discharged from the boom cylinder <NUM>, which will be described with reference to <FIG> etc..

Referring back to <FIG>, the motion sensor <NUM> acquires information about an upward operation and a downward operation of the boom <NUM>. To this end, a sensor that measures upward angle/upward acceleration/stroke of the boom <NUM> or a sensor that measures operation amount/operation time of the operation lever <NUM> may be employed as the motion sensor <NUM>.

The work selector <NUM> is provided to select next works to be performed by an operator. The controller <NUM> can predict information about an upward operation and a downward operation of the boom <NUM> during working from a selected work. The work selector <NUM> may be a manual button for selecting exemplary works or a touch button on a control screen.

The operation lever <NUM> produces instructions for an upward operation and a downward operation of the boom <NUM> when being operated by the operator, and inputs the instructions to the controller <NUM>.

The memory <NUM> stores information on a predicted downward mode associated with a downward operation of the boom <NUM> and a target pressure of the accumulator <NUM> (see <FIG>). The predicted downward mode is divided into a first predicted downward mode and a second predicted downward mode on the basis of the downward acceleration force of the boom <NUM>. The downward acceleration force is larger in the first predicted downward mode than in the second predicted downward mode. The target pressure is a target pressure value for setting the dischargeable lowest limit pressure of the accumulator <NUM>. The dischargeable lowest limit pressure means the lower limit of pressure that the accumulator <NUM> can have in consideration of the efficiency of recuperating energy from the boom cylinder <NUM> under the assumption that a pressurized oil is maximally discharged and sent to the assist motor <NUM> from the accumulator <NUM>.

The target pressure may be divided into a first target pressure and a second target pressure higher than the first target pressure. A control program may be stored in the memory <NUM>. The control program may contain instructions to correspond the first target pressure with the first predicted downward mode and the second target pressure with the second predicted downward mode.

The energy recuperation method is described hereafter with reference to <FIG> on the basis of the above description.

<FIG> is a flow chart illustrating an energy recuperation method for construction equipment according to another embodiment of the present invention.

Referring to this figure (and <FIG>), the energy recuperation method may include determining a predicted downward mode (S1), regulating a dischargeable lowest limit pressure of the accumulator (S3), and charging the accumulator (S5).

First, in the determining of the predicted downward mode (S1), the controller <NUM> predicts which mode the boom <NUM> is turned down in after an upward operation. As described above, the controller <NUM> determines whether the predicted downward mode is the first predicted downward mode or the second predicted downward mode. The predicted downward modes are obtained by predicting actual downward operations of the boom <NUM>, but the actual downward operations may not follow the predicted downward modes.

In the regulating of the dischargeable lowest limit pressure of the accumulator (S3), the controller <NUM> differently regulates the dischargeable lowest limit pressure of the accumulator <NUM>, depending on the predicted downward modes. In other words, the controller <NUM> should increase or decrease the dischargeable lowest limit pressure of the accumulator <NUM>.

In the charging of the accumulator (S5), the controller <NUM> opens the charge valve <NUM> so that the accumulator <NUM> is charged with the pressurized oil in the chamber A 41a of the boom cylinder <NUM> through the charge passage <NUM>. The accumulator <NUM> is charged while the boom <NUM> is actually turned down. In detail, the pressurized oil in the chamber A 41a of the boom cylinder <NUM> is not discharged to the oil tank <NUM>, but supplied into the accumulator <NUM> to turn down the boom <NUM>, thereby recuperating the energy of the pressurized oil. Further, as the pressurized oil in the chamber A 41a is discharged to the accumulator <NUM>, the boom <NUM> is freely dropped by its own weight.

The controller <NUM> can regulate the flow rate of the pressurized oil to be supplied into the accumulator <NUM> by controlling the charge valve <NUM>. The control of a flow rate is in connection with the pressure of the pressurized oil that is supplied into the accumulator <NUM>. Accordingly, as the pressure of the pressurized oil is regulated, the speed of the pressurized oil discharged from the chamber A 41a can be regulated. This means that the downward speed of the boom <NUM> is regulated, so the response speed of the excavator <NUM> can be regulated.

The determining of the predicted downward mode (S1) is described hereafter with reference to <FIG>.

<FIG> is a flow chart illustrating in detail the determining of the predicted downward mode (S1).

Referring to this figure (and <FIG>), the controller <NUM> analyzes first (actual) upward and downward operations of the boom <NUM> to determine a predicted downward mode of the boom <NUM> (S11). Operation information about one or several upward operations and downward operations of the boom <NUM> is stored in the memory <NUM> to analyze operations of the boom <NUM>. The operation information may include upward angle/acceleration force or the like when the boom <NUM> is turned up and downward angle/acceleration force when the boom <NUM> is turned down. The controller <NUM> can analyze the upward and downward operations for those operations with reference to the memory <NUM>.

Next, the controller <NUM> determines whether it is possible to acquire upward/downward operation pattern information through the operation analysis, and if possible, it can acquire the information (S13 and S15). The upward/downward operation pattern information is defined by finding predetermined patterns in the upward operations and the downward operations from the operation information. The upward/downward operation pattern information may include, for example, information that the boom <NUM> is quickly turned up and also quickly turned down. Further, the upward/downward operation pattern information may include information about the interval between the end of the upward operation and the beginning of the downward operation. Accordingly, the controller <NUM> can determine when to charge the accumulator <NUM> on the basis of the information about the interval.

The controller <NUM> may refer to only upward operation pattern information as a part of the upward/downward operation pattern information (S17). The upward operation pattern information means which pattern the upward/downward operation shows. For example, the upward/downward operation pattern information is information about whether the boom <NUM> has been turned up a little or a lot. Under a common work environment, when the boom <NUM> has been turned up a little, the boom <NUM> will be turned down at a low acceleration force, while when the boom <NUM> has been turned up a lot, the boom <NUM> will be turned down at a large acceleration force. The controller <NUM> can determine the predicted downward mode on the basis of this estimation. The upward operation pattern information can be acquired by analyzing upward factor information associated with the upward operation of the boom <NUM>. The upward factor information, for example, may be any one of an upward acceleration value of the boom <NUM>, an upward stroke value of the boom cylinder <NUM> driving the boom <NUM>, and the operation amount or operation time of the operation lever <NUM> driving the boom cylinder <NUM>.

Accordingly, it is possible to determine a predicted downward mode of the boom <NUM> as a first predicted downward mode and a second predicted downward mode on the basis of the information about the upward operations and the downward operations included in the upward/downward operation pattern information (S19). For example, if the downward operation with large downward acceleration force is repeated after the upward operation, the controller <NUM> can determine the predicted downward mode as the first predicted downward mode.

Unlikely, the controller <NUM> can determine the predicted downward mode from an upward operation immediately before a downward operation of the boom <NUM> on the basis of the upward operation pattern information. For example, if the boom <NUM> is turned up a little in the upward operation (the upward stroke value is smaller than a reference stroke value), it is possible to determine the predicted downward mode as the second predicted downward mode by predicting that the downward acceleration force of the boom <NUM> would also be small while the boom <NUM> is turned down. Unlikely, if the upward stroke value is larger than the reference stroke value, it is possible to determine the predicted downward mode as the first predicted downward mode.

Further, the controller <NUM> can determine a predicted downward mode of the boom <NUM> as one of a first predicted downward mode and a second predicted downward mode in the above work on the basis of work inputted by an operator through the work selector <NUM>. For example, if an operate selects grading, the controller <NUM> can predict that the downward acceleration force of the boom <NUM> would be small on the basis of a grading pattern. Accordingly, the controller <NUM> can determine the predicted downward mode as the second predicted downward mode.

<FIG> is a flow chart illustrating in detail the regulating of the dischargeable lowest limit pressure of the accumulator shown in <FIG> (S3).

Referring to the figure (and <FIG>), depending on whether the predicted downward mode is the first predicted downward mode (S21), the controller <NUM> differently regulates corresponding dischargeable lowest limit pressure of the accumulator <NUM>.

In detail, when the predicted downward mode is a first predicted downward mode, the controller <NUM> determines the dischargeable lowest limit pressure of the accumulator <NUM> as the first target pressure (S23 and S27). Unlikely, when the predicted downward mode is a second predicted downward mode, the controller <NUM> determines the dischargeable lowest limit pressure of the accumulator <NUM> as the second target pressure (S25 and S29).

In order to finally set the dischargeable lowest limit pressure to the first target pressure, the controller <NUM> opens the assist valve <NUM> so that the pressurized oil charged in the accumulator <NUM> is supplied to the assist motor <NUM> (S31). If the pressurized oil is being supplied to the assist motor <NUM>, the controller <NUM> can keep the pressurized oil being supplied for a predetermined time. Accordingly, the dischargeable lowest limit pressure of the accumulator <NUM> is reduced to the first target pressure.

On the contrary, in order to finally set the dischargeable lowest limit pressure to the second target pressure, the controller <NUM> closes the assist valve <NUM> so that the pressurized oil in the accumulator <NUM> is maintained therein. Accordingly, the pressurized oil is not supplied to the assist motor <NUM> (S33). If the pressurized oil is being supplied to the assist motor <NUM>, the controller <NUM> can stop the supply to the assist motor <NUM>. Accordingly, the dischargeable lowest limit pressure of the accumulator <NUM> can reach the second target pressure higher than the first target pressure.

With the dischargeable lowest limit pressure of the accumulator <NUM> reaching the second target pressure, the accumulator <NUM> can be additionally charged with the pressurized oil in the swing module <NUM> after the accumulator <NUM> is charged with the pressurized oil from the boom cylinder <NUM>. This is a method of additionally recuperating energy from the pressurized oil that is discharged from the swing module <NUM> while the swing module <NUM> stops a swing operation.

Energy recuperation efficiency while the accumulator <NUM> is charged with the pressurized oil discharged from the boom cylinder <NUM> is described hereafter.

<FIG> is a graph showing pressure changes of a boom cylinder and an accumulator while a work unit is turned down in a first predicted downward mode.

Referring to this figure (and <FIG>), when an operator rapidly operates the operation lever <NUM> to turn down the boom <NUM>, the controller <NUM> is supposed to quickly discharge pressurized oil in the chamber A 41a of the boom cylinder <NUM>.

The controller <NUM> has determined the predicted downward mode as the first predicted downward mode by predicting this situation in advance. The controller <NUM> has set the dischargeable lowest limit pressure of the accumulator <NUM> to the first target pressure before the boom <NUM> is actually turned down.

Accordingly, even if the pressurized oil in the chamber A 41a is quickly discharged and the pressure CP1 in the chamber A 41a is greatly reduced, the minimum of the pressure of the pressurized oil discharged from the chamber A 41a can be regulated to be slightly larger than or equivalent to the first target pressure AP1. Therefore, most of the pressurized oil in the chamber A 41a can be supplied into the accumulator <NUM> without being discharged to the oil tank <NUM>. Further, as the accumulator <NUM> is charged with the pressurized oil, the size of the first target pressure AP1 constructs a gradually increasing line.

Accordingly, all of the pressurized oil discharged from the boom cylinder <NUM> is restored, so the energy recuperation efficiency can be maximized. Further, since the pressurized oil is quickly discharged from the boom cylinder <NUM>, the response speed for the downward operation of the boom <NUM> to operation for downward by an operator can be increased.

If the dischargeable lowest limit pressure of the accumulator <NUM> has reached the second target pressure, the controller <NUM> cannot rapidly discharge the pressurized oil in the chamber A 41a in order to increase the energy recuperation efficiency. This reduces the response speed for the downward operation of the boom <NUM>, which may cause complaint of the operator.

<FIG> is a graph showing pressure changes of a boom cylinder and an accumulator while a work unit is turned down in a second predicted downward mode.

Referring to this figure (and <FIG>), when an operator smoothly pulls the operation lever <NUM> to turn down the boom <NUM>, the controller <NUM> is supposed to discharge only slightly the pressurized oil in the chamber A 41a of the boom cylinder <NUM>.

The controller <NUM> has determined the predicted downward mode as the second predicted downward mode by predicting this situation in advance. The controller <NUM> has set the dischargeable lowest limit pressure of the accumulator <NUM> to the second target pressure CP2 before the boom <NUM> is actually turned down.

Accordingly, even if the pressurized oil in the chamber A 41a is slowly discharged and the pressure CP2 in the chamber A 41a is slightly reduced, the minimum of the pressure of the pressurized oil discharged from the chamber A 41a can be regulated to be slightly larger than or equivalent to the second target pressure AP2. Therefore, most of the pressurized oil discharged from the chamber A 41a can be supplied into the accumulator <NUM> without being discharged to the oil tank <NUM>. Further, as the accumulator <NUM> is charged with the pressurized oil, the size of the second target pressure AP2 constructs a gradually increasing line.

It can be seen that the pressure difference L1 between the pressure CP2 of the pressurized oil in the chamber A 41a and the second target pressure AP2 is smaller than the pressure difference L2 between the pressure CP2 of the pressurized oil in the chamber A 41a and the first target pressure AP1. This means that it is possible to reduce a loss of energy due to a pressure difference by regulating the dischargeable lowest limit pressure of the accumulator <NUM> to the second target pressure AP2 rather than the first target pressure AP1.

<FIG> is a conceptual view showing the main configuration of an energy recuperation system for construction equipment according to another embodiment of the present invention.

Referring to <FIG>, construction equipment <NUM> is similar to the construction equipment <NUM> of the previous embodiment for the most part, but is different from the construction equipment <NUM> having only one accumulator <NUM> in that it has a plurality of sub-accumulators.

Three sub-accumulators <NUM>, <NUM>, and <NUM> are exemplified as the plurality of sub-accumulators. The sub-accumulators <NUM>, <NUM>, and <NUM> are connected in parallel to a charge passage <NUM>. The sub-accumulators <NUM>, <NUM>, and <NUM> have different initial pressures. The initial pressures mean precharged gas pressure of the sub-accumulators <NUM>, <NUM>, and <NUM>. For example, the initial pressures of a first sub-accumulator <NUM>, a second sub-accumulator <NUM>, and a third sub-accumulator <NUM> may be <NUM> bar, <NUM> bar, and <NUM> bar, respectively. In this configuration, the pressure of a boom cylinder <NUM> is higher than the initial pressure of the third sub-accumulator <NUM>, for example, may be <NUM> bar.

According to this configuration, the sub-accumulators <NUM>, <NUM>, and <NUM> can be sequentially charged with pressurized oil that is discharged from a chamber A 141a through the charge passage <NUM> during a downward operation of the boom cylinder <NUM>.

The charging process is described hereafter in detail with reference to <FIG>.

<FIG> is a graph showing pressure changes of a boom cylinder and an accumulator while a work unit is turned down in a first predicted downward mode in the construction equipment <NUM> shown in <FIG>.

Referring to this figure (and <FIG>), when an operator rapidly pulls the operation lever <NUM> to turn down the boom <NUM>, the controller <NUM> is supposed to quickly discharge pressurized oil in the chamber A 141a of the boom cylinder <NUM>.

The controller <NUM> has determined the predicted downward mode as the first predicted downward mode by predicting this situation in advance. The controller <NUM> has set the dischargeable lowest limit pressure of the accumulator to the first target pressure before the boom <NUM> is actually turned down. As a detailed method for this purpose, the controller <NUM> opens a charge valve <NUM> so that one, which has an initial pressure corresponding to the first target pressure, of the sub-accumulators <NUM>, <NUM>, and <NUM>, is selected and charged with pressurized oil in the chamber A 141a. If the dischargeable lowest limit pressure of the accumulator has to be set to the second target pressure, the pressurized oil discharged from the chamber A 141a may be supplied into the sub-accumulator having an initial pressure corresponding to the second target pressure of the sub-accumulators <NUM>, <NUM>, and <NUM>. This is because the pressurized oil cannot be supplied into sub-accumulators having an initial pressure lower than the second target pressure.

Accordingly, when the pressurized oil in the chamber A 141a is discharged, the pressure change of the accumulator does not follow the existing graph AP1, but follows a pressure change graph APC by combination of the three sub-accumulators <NUM>, <NUM>, and <NUM>. In other words, the first sub-accumulator <NUM> having the lowest initial pressure to the third sub-accumulator <NUM> having the highest initial pressure can be sequentially charged with the pressurized oil.

When the pressure change of the accumulator follows the graph AP1, the dischargeable lowest limit pressure of the accumulator is higher than the pressure of the pressurized oil in the loss period G, so the pressurized oil cannot be supplied into the accumulator. Accordingly, the pressurized oil in the chamber A 141a has to be sent to the oil tank <NUM>, so energy cannot be recuperated from the pressurized oil.

Unlikely, when the pressure change of the accumulator follows a new graph APC, the pressure of the pressurized oil is higher than the dischargeable lowest limit pressure of the accumulator even in the loss period G, so the pressurized oil cannot be supplied into the accumulator.

Referring to <FIG>, construction equipment <NUM> according to a new embodiment, similar to the construction equipment <NUM> of the previous embodiment, has a plurality of sub-accumulators <NUM>, <NUM>, and <NUM> having different initial pressures as accumulators. The initial pressures of the sub-accumulators <NUM>, <NUM>, and <NUM> may be <NUM> bar, <NUM> bar, and <NUM> bar, respectively, the same as in the previous embodiment.

The sub-accumulators <NUM>, <NUM>, and <NUM> are connected to each other by inflow passages 269a, 269b, and 269c in parallel with a charge passage <NUM>. Selection valves 279a, 279b, and 279c are respectively disposed in the inflow passages 269a, 269b, and 269c. The controller <NUM> can make the sub-accumulators <NUM>, <NUM>, and <NUM> be objects to be charged or not with pressurized oil by selectively opening/closing the selection valves 279a, 279b, and 279c.

Further, check valves 279d and 279e may be disposed between the inflow passages 269a, 269b, and 269c. The check valves 279d and 279e allow sub-accumulators having a higher initial pressure to be charged with the pressurized oil as the pressure of the pressurized oil increases after sub-accumulators having a lower initial pressure is charged with the pressurized oil, but does not allow for the opposite case.

A charge operation in the construction equipment <NUM> is described hereafter in detail with reference to <FIG>.

<FIG> is a graph showing pressure changes of a boom cylinder and an accumulator while a work unit is turned down in a second predicted downward mode in the construction equipment <NUM> shown in <FIG>.

Referring to this figure (and <FIG>), when an operator smoothly pulls the operation lever <NUM> to turn down the boom <NUM>, the controller <NUM> is supposed to only slightly discharge pressurized oil in the chamber A 241a of the boom cylinder <NUM>.

The controller <NUM> has determined the predicted downward mode as the second predicted downward mode by predicting this situation in advance. Accordingly, the controller <NUM> has set the dischargeable lowest limit pressure of an accumulator to the second target pressure before the boom <NUM> is actually turned down.

As a detailed method of setting the second target pressure, the controller <NUM> opens the charge valve <NUM> and opens only a second selection valve 279b of the selection valves 279a, 279b, and 279c. Accordingly, the pressurized oil in the boom cylinder <NUM> is supplied first into the second sub-accumulator <NUM>. Thereafter, when the pressure of the pressurized oil increases, the pressurized oil can be supplied a third sub-accumulator <NUM> through a second check valve 279e. This process can be seen from a pressure change graph APS showing the actual charge process of an accumulator. Accordingly, the two sub-accumulators <NUM> and <NUM> are sequentially charged with the pressurized oil, but the initial pressures are different, so the dischargeable lowest limit pressures of the accumulators can reach the first target pressure and the second target pressure with an interval.

For reference, another pressure change graph APC of the accumulators show a pressure change when the first selection valve 279a is opened with the charge valve <NUM> by the controller <NUM> and the first sub-accumulator <NUM> to the third sub-accumulator <NUM> are sequentially charged with the pressurized oil.

As a result, since the controller <NUM> opens not the first selection valve 279a, but the second selection valve 279b, it is possible to set the dischargeable lowest limit pressure of the accumulator to the second target pressure. Accordingly, it is possible to prevent a decrease in energy recuperation ratio due to a loss of pressure while an accumulator is charged with the pressurized oil.

The energy recuperation systems and methods for construction equipment described above are not limited to the configurations and operation methods of the embodiments described above. The embodiments may be selectively partially or fully combined for various modifications.

Claim 1:
An energy recuperation system for construction equipment (<NUM>), comprising:
an actuator (<NUM>, <NUM>, <NUM>) configured to drive an upward operation and a downward operation of a work unit (<NUM>, <NUM>, <NUM>);
an accumulator (<NUM>) connected to the actuator; and
a controller (<NUM>), characterized in that the controller is configured to determine a predicted downward mode associated with the downward operation of the work unit, to regulate an dischargeable lowest limit pressure of the accumulator (<NUM>) to a target pressure corresponding to the predicted downward mode, and to charge the accumulator having the dischargeable lowest limit pressure regulated to the target pressure with pressurized oil discharged from the actuator during the downward operation of the work unit (<NUM>, <NUM>, <NUM>) such that an energy recuperation is achieved.