Power generation control method of hybrid construction machine and hybrid construction machine

A power generation control method of a hybrid construction machine capable of maintaining voltage of a capacitor in an appropriate range while minimizing capacitance of the capacitor and of surely preventing a system from being rendered inoperative, and the hybrid construction machine are provided. For this purpose, swing power corresponding to electric power consumed by a swing motor for swinging a part of a body relative to other parts is sequentially calculated, a value of the calculated swing power is converted to a smaller value, a power generation command of a generator motor is sequentially generated using the converted value, and the generated power generation command is output to an inverter for driving the generator motor.

TECHNICAL FIELD

The present invention relates to a power generation control method of a hybrid construction machine provided with an engine and a generator motor coupled to each other as drive sources and with a swing motor for swinging a part of a body relative to other parts, and the hybrid construction machine.

BACKGROUND ART

Conventionally, in a hybrid vehicle provided with the engine and the generator motor coupled to each other as the drive sources, various approaches are made regarding power generation control of the generator motor at the time of operation.

For example, as a technique in the hybrid construction machine such as a hydraulic shovel provided with the swing motor for swinging a part of the vehicle relative to other parts, it is disclosed the technique to change a target power storage amount of a capacitor based on various energies of an operation machine to perform power generation control in order to obtain a small capacitor, which is a power storage device, and a longer operating life thereof (refer to patent document 1, for example).

It is difficult to estimate electric power consumed by the swing motor in the hybrid construction machine provided with the swing motor. This is because there are a variety of works and there is variation in lever operation by the operator. In the above-described conventional technique, the power generation control is performed substantially independently of the electric power consumed by the swing motor based on characteristics of such hybrid construction machine.Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2002-359935

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

However, there was a possibility that voltage of the capacitor rapidly increased and deviated from an appropriate range at the time of regeneration of the swing motor, when the power generation control was performed without sufficiently taking into account the electric power consumed by the swing motor. When the voltage of the capacitor deviates from the appropriate range, the system is rendered inoperative and the operating life of the capacitor becomes short. Therefore, it is considered to inhibit rapid increase in the voltage of the capacitor by increasing capacitance of the capacitor; however, the capacitor gets larger in this case and there was a problem of a space on which the capacitor is mounted, and weight and cost of the capacitor.

The present invention is made under above-described circumstances and an object thereof is to provide the power generation control method of the hybrid construction machine capable of maintaining the voltage of the capacitor in the appropriate range while minimizing the capacitance of the capacitor and of surely preventing the system from being rendered inoperative, and the hybrid construction machine.

Means for Solving Problem

According to an aspect of the present invention, a power generation control method of a hybrid construction machine provided with an engine and a generator motor coupled to each other, an inverter connected to the generator motor for driving the generator motor, a capacitor connected in parallel to the inverter for storing electric power generated by the generator motor and supplying electric power to the generator motor, and a swing motor supplied with electric power from the generator motor and the capacitor for swinging a part of a body relative to other parts, includes: a swing power calculating step of sequentially calculating swing power corresponding to electric power consumed by the swing motor; a swing power converting step of converting a value of the swing power at the time of power running of the swing motor calculated at the swing power calculating step to a smaller value; a power generation command generating step of sequentially generating a power generation command of the generator motor using the value converted at the swing power converting step; and an outputting step of outputting the power generation command generated at the power generation command generating step to the inverter.

Advantageously, in the power generation control method of the hybrid construction machine, the swing power converting step converts the value of the swing power such that, even when voltage of the capacitor changes at the time of regeneration of the swing motor, the voltage is within a predetermined range.

Advantageously, in the power generation control method of the hybrid construction machine, the swing power converting step carries out an operation of multiplying the value of the swing power by a coefficient smaller than 1.

Advantageously, in the power generation control method of the hybrid construction machine, the swing power converting step changes the coefficient to multiply the value of the swing power according to a predetermined measured value measured inside or outside the hybrid construction machine.

Advantageously, the power generation control method of the hybrid construction machine further includes: a target voltage setting step of setting target voltage of the capacitor according to a motor speed of the swing motor; a voltage difference calculating step for calculating difference between the target voltage set at the target voltage setting step and the voltage of the capacitor; and a voltage difference converting step for converting the voltage difference calculated at the voltage difference calculating step to a physical amount having same dimension as the swing power. The power generation command generating step calculates a sum of the value converted at the voltage difference converting step and the value converted at the swing power converting step, and generates the power generation command using the calculated sum.

According to another aspect of the present invention, a hybrid construction machine provided with an engine and a generator motor coupled to each other as drive sources and with a swing motor for swinging a part of a body relative to other parts, includes: an inverter connected to the generator motor for driving the generator motor; a capacitor connected in parallel to the inverter for storing electric power generated by the generator motor and supplying electric power to the generator motor; and a control unit for sequentially calculating swing power corresponding to electric power consumed by the swing motor, converting a value of the calculated swing power to a smaller value, sequentially generating a power generation command of the generator motor using the converted value, and outputting the generated power generation command to the inverter.

Advantageously, in the hybrid construction machine, the control unit sets target voltage of the capacitor according to a motor speed of the swing motor, calculates voltage difference between the set target voltage and voltage of the capacitor, converts the calculated voltage difference to a physical amount having same dimension as the swing power, and calculates a sum of a value obtained by converting the voltage difference and a value obtained by converting the swing power and generates the power generation command using the calculated sum.

Effect of the Invention

According to the present invention, the swing power corresponding to the electric power consumed by the swing motor is sequentially calculated, the calculated swing power is converted to a smaller value, the power generation command of the generator motor is sequentially generated using the converted value, and the generated power generation command is output to an inverter for the generator motor, so that the generator motor may generate power in consideration of energy to be returned from the swing motor at the time of regeneration. Therefore, it becomes possible to realize control within an operating voltage range in which the capacitor may offer performance thereof without unnecessarily increasing the capacitance of the capacitor, and it becomes possible to surely prevent the system from being rendered inoperative due to the deviation from the operating voltage range thereof or the like.

EXPLANATIONS OF LETTERS OR NUMERALS

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Hereinafter, a best mode for carrying out the present invention (hereinafter, referred to as an “embodiment”) is described with reference to attached drawings.

First Embodiment

FIG. 1is a view showing a configuration of a substantial part of a hybrid construction machine according to a first embodiment of the present invention. The hybrid construction machine according to the first embodiment has an engine and a generator motor coupled to each other as drive sources, and has an electric swing function. Although a case of a hydraulic shovel having an excavation function is described as the hybrid construction machine in the first embodiment, this is no more than one example.

FIG. 2is a view showing an external configuration of the hydraulic shovel, which is the hybrid construction machine. A hydraulic shovel1shown in the drawing is provided with a running body101having a right-and-left pair of crawler tracks, and a swing body102located above the running body101and pivotable about a swing axis oriented in a predetermined direction relative to the running body101. In addition, the hydraulic shovel1has an operating machine for excavating composed of a boom103, an arm104and a bucket105. Out of them, the boom103is connected so as to be rotatable in an up and down direction relative to the running body101.

Next, an internal configuration of the hydraulic shovel1is described with reference toFIG. 1. The hydraulic shovel1is provided with an engine2, which is the drive source, a generator motor3and a hydraulic pump4each having a drive axis coupled to an output axis of the engine2, an inverter5connected to the generator motor3to drive the generator motor3, and a capacitor6connected in parallel to the inverter5to store electric power generated by the generator motor3and supply the electric power to the generator motor3.

Also, the hydraulic shovel1is provided with a swing motor7, which is the drive source for swinging the swing body102, a swing inverter8connected in parallel to the capacitor6and connected in parallel to the inverter5for driving the swing motor7, and swing machinery9coupled to a drive axis of the swing motor7for swinging the swing body102.

Further, the hydraulic shovel1is provided with a controller10for electronically controlling the engine2, the hydraulic pump4, the inverter5and the swing inverter8, and an operation input unit11composed of an operating lever or the like for an operator to input desired operation.

The hydraulic pump4is connected to various operation valves such as an boom operation valve21, an arm operation valve22, an bucket operation valve23, a left running operation valve24, and a right running operation valve25, through piping. The hydraulic pump4is a variable displacement type, and capacity thereof changes due to a change in tilt angle of a tilted plate.

Pressurized oil discharged from the hydraulic pump4is supplied to a boom hydraulic cylinder31, a arm hydraulic cylinder32, a bucket hydraulic cylinder33, a left running hydraulic cylinder34and a right running hydraulic cylinder35, which serve as actuators, through the boom operation valve21, the arm operation valve22, the bucket operation valve23, the left running operation valve24, and the right running operation valve25, respectively. This allows the boom103, the arm104, the bucket105, the left crawler track and the right crawler track to operate.

The controller10receives input of a engine speed of the engine2, discharge pressure of the hydraulic pump4, voltage of the capacitor6, direct-current electricity to be input to the swing inverter8(with a reversed sign at the time of output), a motor speed of the swing motor7, and an operational amount of the operation input unit11by the operator, each measured by predetermined measuring means, and drive-controls the hydraulic shovel1based on the input of the various measured values. The various measured values are measured substantially in real time. The controller10has a memory10afor storing a program for controlling various operations of the hydraulic shovel1and the above-described various measured values.

FIG. 3is a flowchart showing an overview of a process of a power generation control method of the hybrid construction machine according to the first embodiment.

First, the controller10calculates swing power consumed by the swing motor7(step S1). The controller10performs a process to be described later only when the swing power of the swing motor7is positive (at a time of power running) (step S2, Yes). When the swing power of the swing motor7is negative (at a time of regeneration) (step S2, No), the procedure returns to the step S1.

When the swing power calculated by the controller10is positive, the controller10reads a value of the swing power from the memory10a, and converts the read value of the swing power to a smaller value (step S3). Next, the controller10generates a power generation command to the generator motor3using the converted swing power (step S4), and outputs the generated power generation command to the inverter5(step S5). Thereafter, the controller10returns to the step S1.

FIG. 4is a view schematically showing the overview of the process of the power generation control method of the hybrid construction machine described above. A curve C1represents a change over time of an amount of power generation G generated by the generator motor3based on the power generation command output by the controller10at the step S5. In addition, a curve C2represents the change over time of the amount of power generation G of the generator motor3controlled by a conventional power generation control method. That is to say, the curve C2represents the change over time of the amount of power generation G generated by the generator motor3based on the power generation command output by the controller10when the process at the step S3is not performed.

A curve C3represents a change over time of swing power PSof the swing motor7. In the curve C3, a range of PS>0 corresponds to the time of power running of the swing motor7, and a range of PS<0 corresponds to the time of generation of the swing motor7. A size of the swing power PSis determined according to the operational amount of the operating lever of the operation input unit11by the operator, and when the operating lever of the operation input unit11returns to an original position, the swing motor7performs regenerative operation. In general, the electric power consumed at the time of power running of the swing motor7is larger than the electric power generated at the time of regeneration of the swing motor7.

A curve C4represents a change over time of capacitor voltage V of the capacitor6in a case in which the amount of power generation G of the generator power3changes over time according to the curve C1and which the swing power PSof the swing motor7changes over time according to the curve C3. Also, a curve C5represents the change over time of the capacitor voltage V in a case in which the amount of power generation G of the generator motor3changes over time according to the curve C2and which the swing power PSof the swing motor7changes over time according to the curve C3. InFIG. 4, an operating voltage range in which the capacitor6may offer performance thereof is set to (V1, V2).

In the first embodiment, in order to supply the swing power PSconsumed at the time of power running of the swing motor7, the electric power generated by the generator motor3is not sufficient and the electric power from the capacitor6is also required. Therefore, the capacitor voltage V decreases at the time of power running of the swing motor7. On the other hand, the electric power is returned from the swing motor7to the capacitor6at the time of regeneration of the swing motor7, so that an electric charge amount of the capacitor6increases and the capacitor voltage V increases.

It is preferable that the controller10controls such that energy obtained by temporally integrating a decrease in the amount of power generation G (area of a range D1enclosed by the curves C1and C2) substantially equals to energy obtained by temporally integrating the electric power generated at the time of regeneration of the swing motor7(area of a range D2enclosed by the curve C3and a t-axis). Since the energy corresponding to the decrease in the amount of power generation G equals to the energy supplied by the capacitor6at the time of power running of the swing motor7, by performing the above-described control, the energy supplied by the capacitor6at the time of power running of the swing motor7substantially equals to the energy returned to the capacitor6at the time of regeneration of the swing motor7. Therefore, the capacitor voltage V is substantially the same before and after the generation of the swing power PSby the swing motor7(V0inFIG. 4).

Herein, the conventional power generation control method is described for comparison. In a case of the conventional power generation control method, it is not necessary that the capacitor6supply the electric power at the time of power running of the swing motor7. Therefore, the capacitor voltage V is constant at the time of power running of the swing motor7. Also, since the electric power is returned from the swing motor7to the capacitor6at the time of regeneration of the swing motor7, the capacitor voltage V increases from a value V0before generation of the swing power PSby the swing motor7. In the curve C5shown inFIG. 4, a maximum value Vmax of the capacitor voltage V is higher than an upper limit value V2of the operating voltage range of the capacitor6.

In this manner, in the conventional power generation control method, there has been a case in which the capacitor voltage V deviated from the operating voltage range of the capacitor6and the system was rendered inoperative. On the other hand, according to the first embodiment, when supplying the electric power to the swing motor7, the amount of power generation of the generator motor3is decreased and the decrease is compensated by the supply from the capacitor6, so that it is possible to always maintain the capacitor voltage V in an operable range. Therefore, stable system operation may be realized.

FIG. 5is a process flow diagram showing an overview of a more detailed process of the power generation control method of the hybrid construction machine described with reference toFIGS. 3 and 4. The controller10sequentially calculates the electric power of the swing inverter8(swing inverter electric power P) as the swing power consumed by the swing motor7to store in the memory10a(step S11). The swing inverter electric power P is calculated by multiplying the measured value of the voltage of the capacitor6by the measured value of the direct-current electricity input to the swing inverter8.FIG. 6is a view showing an example of a change over time of the swing inverter electric power P when the operator carries out certain operation (hereinafter, referred to as “operation A”). A curve L1shown inFIG. 6varies while repeating the power running (P>0) and the regeneration (P<0), and the maximum value at the time of power running is Pmax.

Thereafter, the controller10performs a process to be described later only when the swing inverter electric power P is positive, that is to say, at the time of power running (step S12, Yes). When the swing inverter electric power P is negative, that is to say, at the time of regeneration (step S12, No), the procedure returns to the step S11.

When the swing inverter electric power P is positive, the controller10carries out an operation of multiplying the swing inverter electric power P by a predetermined coefficient K2(step S13). The coefficient K2is a constant smaller than 1 and a specific value thereof is set while taking into account the electric power returned to the capacitor6by the power generation by the swing motor7at the time of regeneration of the swing motor7(corresponding to a range of P<0 inFIG. 6). However, it is physically substantially impossible that the swing motor7returns the electric power, which is larger than that at the time of power running, to the capacitor6at the time of regeneration, so that it is necessary that the coefficient K2be a value not smaller than 0. Meanwhile, the operation giving a value smaller than the swing inverter electric power P may be used as the operation at the step S13, and it is possible to subtract a predetermined constant from the swing inverter electric power P, for example.

The controller10also receives the motor speed of the swing motor7(swing motor speed ω) in real time (step S14).FIG. 7is a view showing an example of a change over time of the swing motor speed ω. A curve L2shown inFIG. 7corresponds to the swing inverter electric power P shown inFIG. 6, and represents the change over time in the same time period as inFIG. 6in which the operator carries out the operation A. In such curve L2, the swing motor7rotates according to a swing direction with a maximum motor speed of ωmax. The rotation of the swing motor7changes according to the lever operation carried out by the operator in the operation input unit11. That is to say, the change over time shown inFIG. 7is that when the operator carries out certain lever operation.

Next, the controller10takes an absolute value of the swing motor speed ω (step S15), and sets target voltage Vcap0of the capacitor6according to this value (step S16).

FIG. 8is a view showing a relationship between (the absolute value of) the swing motor speed ω and the capacitor target voltage Vcap0. In general, the capacitor6has the operating voltage range in which this may offer the performance thereof. Therefore, it is preferable that the capacitor target voltage Vcap0is set to be included in the operating voltage range regardless of the value of the swing motor speed ω. In addition, it is considered that the energy returned at the time of regeneration of the swing motor7is larger with increasing absolute value of the swing motor speed ω, so that it is more preferable that the capacitor target voltage Vcap0is set to be lower with increasing absolute value of the swing motor speed ω, to leave place to store the energy.

A straight line L3shown inFIG. 8is set such that the relationship between the swing motor speed ω and the capacitor target voltage Vcap0satisfies the above-described two characteristics. InFIG. 8, the operating voltage range of the capacitor6is set to (Vcap1, Vcap2). In addition, inFIG. 8, it is also possible to set the range of the value of the capacitor target voltage Vcap0narrower than the operating voltage range (Vcap1, Vcap2) in consideration of a case in which the controller10performs another control.

Meanwhile, it is not necessary that the relationship between the swing motor speed ω and the capacitor target voltage Vcap0be necessarily linear as long as this at least satisfies the above-described two characteristics. Also, it is possible to make the capacitor target voltage Vcap0constant regardless of the swing motor speed ω.

Following the step S16, the controller10calculates difference Vcap0−Vcap between the set capacitor target voltage Vcap0and the voltage Vcap of the capacitor6received in real time (step S17), and multiplies the difference by a coefficient K1(step S18). Herein, the coefficient K1is a predetermined constant, which is the coefficient to convert the voltage difference Vcap0−Vcap obtained at the step S17to an electric power value (dimension of the swing inverter electric power P), and has physical dimension (herein, dimension of current) unlike the above-described coefficient K2. Meanwhile, the physical dimension of K1may be dimension of the capacitor capacitance or dimension of multiplication of the current and the capacitor.

The controller10obtains a sum of P×K2obtained at the step S13and (Vcap0−Vcap)×K1obtained at the step S18(step S19), and generates the power generation command to be output to the inverter5using the sum (step S20). At the step S20, the controller10generates the power generation command only when the output at the step S19is positive, and outputs power generation capacity of the generator motor3as the power generation command when the generated power generation command excesses the power generation capacity of the generation motor3. Also, at the step S20, a filter of a predetermined frequency may be interposed.

In a value of the sum obtained at the step S19, P×K2is basically dominant, and it is set that a contribution of (Vcap0−Vcap)×K1increases when the hydraulic shovel1performs unusual operation. Specifically, there is a tendency that the value of Vcap0−Vcap is larger at the time of unusual operation than at the time of normal operation. As the unusual operation herein used, a case in which the bucket105suddenly collides with something to stop, for example, is considered. When the bucket105suddenly stops due to an external cause, the swing motor speed ω suddenly becomes 0, so that the capacitor target voltage Vcap0suddenly becomes large (refer toFIG. 8). As a result, the difference Vcap0−Vcap between the same and the capacitor voltage Vcap becomes large and a ratio of the contribution of (Vcap0−Vcap)×K1in the sum obtained at the step S19increases.

After that, the controller10outputs the generated power generation command to the inverter5. The inverter5drives the generator motor3according to the input power generation command. This allows the generator motor3to generate electric power (step S21).

According to the power generation by the generator motor3, the capacitor voltage Vcap changes over time. As described above, the controller10receives the measured value of the capacitor voltage Vcap substantially in real time (step S22). Therefore, the change in the capacitor voltage Vcap by the power generation by the generator motor3is transmitted to the controller10substantially in real time.

FIG. 9is a view showing an example of a change over time of the capacitor voltage Vcap. A curve L4shown inFIG. 9corresponds to the swing inverter electric power P shown inFIG. 6and the swing motor speed ω shown inFIG. 7, and represents the change over time in the same time period as inFIGS. 6 and 7in which the operator carries out the operation A. The curve L4always varies within the operating voltage range without deviating from the operating voltage range (Vcap1, Vcap2) of the capacitor6. As is clear from this, according to the power generation control method of the hybrid construction machine according to the first embodiment, it is possible to maintain the voltage of the capacitor6in an appropriate range.

Meanwhile, as described in the above-described step S17, the controller10sequentially uses the measured value of the capacitor voltage Vcap when calculating the voltage difference between the capacitor voltage Vcap and the capacitor target voltage Vcap0.

According to the above-described first embodiment of the present invention, the swing power (swing inverter electric power) corresponding to the electric power consumed by the swing motor is sequentially calculated, the calculated swing power is converted to the smaller value, the power generation command of the generator motor is sequentially generated using the converted value, and the generated power generation command is output to the inverter for the generator motor, so that the generator motor may generate power in consideration of the energy to be returned from the swing motor at the time of regeneration. Therefore, it becomes possible to realize the control of the capacitor within the operating voltage range without unnecessarily increasing the capacitance of the capacitor, and it becomes possible to surely prevent the system failure due to the deviation of the capacitor from the operating voltage range.

Also, according to the first embodiment, the swing power corresponding to the power consumed by the swing motor is sequentially calculated, the calculated swing power is converted to the smaller value, the power generation command of the generator motor is sequentially generated using the converted value, and the generated power generation command is output to the inverter for the generator motor, so that the generator motor may generate power in consideration of the energy to be returned from the swing motor at the time of regeneration. Therefore, it becomes possible to realize the control within the operating voltage range in which the capacitor may offer performance thereof without unnecessarily increasing the capacitance of the capacitor, and it becomes possible to surely prevent the system from being rendered inoperative due to deviation from the operating voltage range thereof or the like.

Meanwhile, although the swing inverter electric power is used as the swing power in the first embodiment, torque and the motor speed of the swing motor may be used instead, or an operational amount of the operation input unit (lever stroke) may be used.

Second Embodiment

FIG. 10is a process flow diagram showing an overview of a process of the power generation control method of the hybrid construction machine according to a second embodiment of the present invention. In the second embodiment, the value of the coefficient K2is changed according to the motor speed ω of the swing motor7when the controller10carries out the operation of multiplying the swing inverter electric power P by the predetermined coefficient K2(step S13′).

FIG. 11is a view showing a relationship between the motor speed ω of the swing motor7and the coefficient K2. In a straight line L5shown inFIG. 11, the coefficient K2gets smaller as the motor speed ω of the swing motor7gets larger. The coefficient K2is thus set because the larger the swing motor speed ω is, the smaller the amount of power generation by the generator motor3may be.

The configuration of the hybrid construction machine and the process of the power generation control method of the hybrid construction machine except the above-described points are the same as those of the above-described first embodiment.

Another Embodiment

Although the best mode for carrying out the invention is described so far, the present invention is not limited only by the above-described two embodiments.FIG. 12is a view showing another setting example of the coefficient K2to be multiplied by the swing inverter output (swing power). A straight line L6shown in the drawing represents a case in which the coefficient K2is changed according to the swing inverter electric power P(>0). In this case, it is necessary to increase the amount of power generation of the generator motor3with increasing swing inverter power P, so that it is configured that the value of the coefficient K2increases with increasing swing inverter electric power P.

FIG. 13is a view showing yet another setting example of the coefficient K2to be multiplied by the swing inverter output (swing power). A straight line L7shown in the drawing represents a case in which the coefficient K2is changed according to an exterior temperature T (centigrade temperature is supposed inFIG. 13). The construction machine is supposed to be used in a wide temperature range from a low temperature of 0 degrees C. or lower to a high temperature (Tmim to Tmax). In general, efficiency of the generator motor3increases with increasing exterior temperature T, so that the higher the exterior temperature T is, the smaller the coefficient K2may be made. Meanwhile, an internal temperature of the capacitor may be used in place of the exterior temperature T.

Although only a case in which the relationship between the coefficient K2and various conditions is linearly changed is described in the above description, the change may be set by an appropriate function.

Also, the value of the coefficient K1to be multiplied by the voltage difference between the capacitor target voltage Vcap0and the capacitor voltage Vcap may be made variable. For example, it may be configured that the controller10performs control to change the value of the coefficient K1, when a time period in which the contribution of (Vcap0−Vcap)×K1is larger than a predetermined reference value in the sum obtained at the step S19inFIG. 5continues for predetermined time. Also, it is possible to convert the voltage difference Vcap0−Vcap by an appropriate function to output, instead of multiplying the coefficient K1.

In this manner, the present invention may include various embodiments not described herein, and it is possible to make various design changes or the like without departing from the scope of technical idea specified by claims.

INDUSTRIAL APPLICABILITY

As described above, the present invention is useful in controlling the power generation of the hybrid construction machine provided with the capacitor as a power storage device and the swing motor.