U.S. patent application number 14/239795 was filed with the patent office on 2014-07-03 for construction machine.
The applicant listed for this patent is Seiji Ishida, Yusuke Kajita, Hideloshi Satake, Shiro Yamaoka. Invention is credited to Seiji Ishida, Yusuke Kajita, Hideloshi Satake, Shiro Yamaoka.
Application Number | 20140188321 14/239795 |
Document ID | / |
Family ID | 47756022 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140188321 |
Kind Code |
A1 |
Ishida; Seiji ; et
al. |
July 3, 2014 |
CONSTRUCTION MACHINE
Abstract
An object of the present invention is to provide a construction
machine that can reduce particulate matter (PM) or nitrogen oxide
(NOx) discharged from an internal combustion engine mounted on the
construction machine. The construction machine 200 includes a
diesel engine 101 controlled based on a torque command, an electric
motor 102 mechanically connected to the diesel engine, an electric
energy storage device 111 that supplies electric power to the
electric motor, and a hydraulic pump 103. The construction machine
performs work by driving the hydraulic pump using the diesel engine
and the electric motor. A speed control device 118 controls a speed
of the electric motor 102 based on a speed command. A torque
limiter 115 obtains the torque command having a rate of change with
time limited based on a torque target.
Inventors: |
Ishida; Seiji; (Tokoy,
JP) ; Satake; Hideloshi; (Ishioka, JP) ;
Kajita; Yusuke; (Ushiku, JP) ; Yamaoka; Shiro;
(Tokoy, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ishida; Seiji
Satake; Hideloshi
Kajita; Yusuke
Yamaoka; Shiro |
Tokoy
Ishioka
Ushiku
Tokoy |
|
JP
JP
JP
JP |
|
|
Family ID: |
47756022 |
Appl. No.: |
14/239795 |
Filed: |
August 10, 2012 |
PCT Filed: |
August 10, 2012 |
PCT NO: |
PCT/JP2012/070557 |
371 Date: |
February 20, 2014 |
Current U.S.
Class: |
701/22 ;
903/902 |
Current CPC
Class: |
B60L 2240/445 20130101;
B60L 2240/421 20130101; B60W 2510/083 20130101; B60W 10/06
20130101; B60L 2270/12 20130101; B60L 1/003 20130101; B60W 20/00
20130101; B60L 7/14 20130101; B60L 2220/14 20130101; B60W 2510/0657
20130101; Y02T 10/62 20130101; B60L 2240/423 20130101; Y02T 10/7072
20130101; B60L 2200/40 20130101; B60W 2050/0055 20130101; B60L
2220/42 20130101; B60W 20/16 20160101; B60W 2510/30 20130101; B60L
58/13 20190201; B60W 2510/0661 20130101; B60L 2240/549 20130101;
Y10S 903/902 20130101; B60L 2240/80 20130101; E02F 9/207 20130101;
B60L 15/20 20130101; B60L 50/61 20190201; B60W 2710/081 20130101;
E02F 3/32 20130101; E02F 9/2075 20130101; Y02T 10/70 20130101; B60L
15/2009 20130101; B60L 50/40 20190201; B60K 6/485 20130101; Y02T
10/64 20130101; B60L 2240/443 20130101; Y02T 10/72 20130101; B60W
2300/17 20130101; B60W 10/08 20130101; B60W 2510/081 20130101 |
Class at
Publication: |
701/22 ;
903/902 |
International
Class: |
B60W 10/06 20060101
B60W010/06; B60W 20/00 20060101 B60W020/00; B60W 10/08 20060101
B60W010/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2011 |
JP |
2011-189555 2011 |
Claims
1. A construction machine including an internal combustion engine
controlled based on a torque command, an electric motor
mechanically connected to the internal combustion engine, an
electric energy storage device that supplies electric power to the
electric motor, and a hydraulic pressure generator, the
construction machine performing work by driving the hydraulic
pressure generator using the internal combustion engine and the
electric motor, the construction machine comprising: first control
means that controls a speed of the electric motor based on a speed
command; and second control means that obtains the torque command
having a rate of change with time limited based on a torque
target.
2. The construction machine according to claim 1, wherein the
internal combustion engine is controlled by a first torque command
obtained based on the speed command and the speed of the internal
combustion engine, and the first control means calculates a second
torque command obtained based on the speed command and the speed of
the electric motor, further includes a high-pass filter that
removes a low-frequency component including a DC component of the
second torque command, and controls the electric motor based on an
output of the high-pass filter.
3. The construction machine according to claim 1, wherein the
electric motor is speed-controlled by the speed command, and torque
of the internal combustion engine is greater than torque of the
electric motor when a rate of change with time in torque of the
hydraulic pressure generator is low, and the torque of the electric
motor is greater than the torque of the internal combustion engine
when the rate of change with time in the torque of the hydraulic
pressure generator is high.
4. The construction machine according to claim 1, wherein the
electric motor is speed-controlled by the speed command, and a
change of a rate of change with time in the torque of the internal
combustion engine is higher than a change of a rate of change with
time in the torque of the hydraulic pressure generator when the
rate of change with time in the torque of the hydraulic pressure
generator is low, and the change of the rate of change with time in
the torque of the internal combustion engine is lower than the
change of the rate of change with time in the torque of the
hydraulic pressure generator when the rate of change with time in
the torque of the hydraulic pressure generator is high.
5. The construction machine according to claim 1, wherein the
torque target is obtained based on a charge amount of the electric
energy storage device.
6. A construction machine comprising: an internal combustion
engine; an electric motor mechanically connected to the internal
combustion engine; an electric energy storage device that supplies
electric power to the electric motor and a hydraulic pressure
generator; the construction machine performing work by driving the
hydraulic pressure generator using the internal combustion engine
and the electric motor; wherein the electric motor is
speed-controlled by a speed command; and torque of the internal
combustion engine is greater than torque of the electric motor when
a rate of change with time in torque of the hydraulic pressure
generator is low; and the torque of the electric motor is greater
than the torque of the internal combustion engine when the rate of
change with time in the torque of the hydraulic pressure generator
is high.
7. A construction machine comprising: an internal combustion
engine; an electric motor mechanically connected to the internal
combustion engine; an electric energy storage device that supplies
electric power to the electric motor and a hydraulic pressure
generator; the construction machine performing work by driving the
hydraulic pressure generator using the internal combustion engine
and the electric motor; wherein the electric motor is
speed-controlled by the speed command; and a change of a rate of
change with time in torque of the internal combustion engine is
higher than a change of a rate of change with time in torque of the
hydraulic pressure generator when the rate of change with time in
the torque of the hydraulic pressure generator is low; and the
change of the rate of change with time in the torque of the
internal combustion engine is lower than the change of the rate of
change with time in the torque of the hydraulic pressure generator
when the rate of change with time in the torque of the hydraulic
pressure generator is high.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to construction
machines and, more particularly, to a construction machine that
performs work hydraulically by driving a hydraulic pressure
generator with an internal combustion engine and an electric
motor.
BACKGROUND ART
[0002] A known technique in a hybrid construction machine
accurately brings an engine to a target operating state by causing
a motor generator to assist the engine or to generate electricity
through an as simple as possible configuration (see, for example,
patent document 1). To achieve that task, the technique disclosed
in patent document 1 incorporates a controller that obtains an
engine speed corresponding to optimum torque of a set speed as a
target speed and performs the following control so as to bring the
engine close to an optimum operating state. Specifically, when the
engine speed is lower than the target speed because of a large load
torque on the engine, the controller causes the motor generator to
operate as an electric motor according to a difference therebetween
to thereby assist torque. When the engine speed is higher than the
target speed because of a small load torque on the engine, the
controller causes the motor generator to operate as a generator
according to the difference therebetween to thereby store the
generated electricity in a battery.
[0003] Another known control technique is, even with a sharp
increase in a hydraulic load, to increase driving power supplied to
a hydraulic pressure generator in response to the increase in the
hydraulic load, while maintaining appropriate operating conditions
of an internal combustion engine (see, for example, patent document
2). To achieve that task, the technique disclosed in patent
document 2, while causing the internal combustion engine to drive
the hydraulic pressure generator, sets a rate of increase in an
output of the internal combustion engine to a predetermined value.
An output upper limit value of the internal combustion engine
obtained from the predetermined value of the rate of increase is
then compared with a driving power requirement obtained from a
hydraulic pressure output that the hydraulic pressure generator is
required to produce. The output of the internal combustion engine
is then controlled so as to be equal to, or smaller than, the
output upper limit value when the driving power requirement exceeds
the output upper limit value.
PRIOR ART DOCUMENTS
Patent Documents
[0004] Patent Document 1: JP-2003-28071-A
[0005] Patent Document 2: JP-2009-216058-A
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0006] The technique disclosed in patent document 1 does not,
however, consider a transient state when the load torque undergoes
a sudden change and thus involves an unavoidable situation in which
a rate of change with time in the output torque of the engine as an
internal combustion engine becomes high. This requires excessive
fuel injection and may produce a large amount of particulate matter
(PM) or nitrogen oxide (NOx).
[0007] The technique disclosed in patent document 2 controls an
electric motor based on the output requirement of the hydraulic
pressure generator and thus requires the output requirement of the
hydraulic pressure generator. With construction machines, however,
it is difficult to identify a load on a work implement, to detect a
flow rate of hydraulic fluid in detail, and thus to accurately
detect or estimate the output requirement. Moreover, because the
electric motor is controlled without having feedback information on
states of the engine, an error involved with the output requirement
hampers accurate control of the rate of change with time in the
engine output torque. For these reasons, a large amount of
particulate matter (PM) or nitrogen oxide (NOx) may be produced, as
with patent document 1.
[0008] An object of the present invention is to provide a
construction machine that can reduce particulate matter (PM) or
nitrogen oxide (NOx) discharged from an internal combustion engine
mounted on the construction machine.
Means for Solving the Problem
[0009] To achieve the foregoing object, the present invention
provides a construction machine including an internal combustion
engine controlled based on a torque command, an electric motor
mechanically connected to the internal combustion engine and an
electric energy storage device that supplies electric power to the
electric motorgenerator. The construction machine performs work by
driving a hydraulic pressure generator using the internal
combustion engine and the electric motor. The construction machine
includes: first control means that controls a speed of the electric
motor based on a speed command; and second control means that
obtains the torque command having a rate of change with time
limited based on a torque target.
[0010] The present invention further provides a construction
machine including an internal combustion engine, an electric motor
mechanically connected to the internal combustion engine and an
electric energy storage device that supplies electric power to the
electric motor. The construction machine performs work by driving a
hydraulic pressure generator using the internal combustion engine
and the electric motor. The electric motor is speed-controlled by a
speed command, and torque of the internal combustion engine is
greater than torque of the electric motor when a rate of change
with time in torque of the hydraulic pressure generator is low, and
the torque of the electric motor is greater than the torque of the
internal combustion engine when the rate of change with time in the
torque of the hydraulic pressure generator is high.
[0011] The present invention still further provides a construction
machine including: an internal combustion engine; an electric motor
mechanically connected to the internal combustion engine; an
electric energy storage device that supplies electric power to the
electric motor; and a hydraulic pressure generator. The
construction machine performs work by driving the hydraulic
pressure generator using the internal combustion engine and the
electric motor. The electric motor is speed-controlled by the speed
command, and a change of a rate of change with time in torque of
the internal combustion engine is higher than a change of a rate of
change with time in torque of the hydraulic pressure generator when
the rate of change with time in the torque of the hydraulic
pressure generator is low, and the change of the rate of change
with time in the torque of the internal combustion engine is lower
than the change of the rate of change with time in the torque of
the hydraulic pressure generator when the rate of change with time
in the torque of the hydraulic pressure generator is high.
[0012] Such arrangements allow the particulate matter (PM) or the
nitrogen oxide (NOx) discharged from the internal combustion engine
mounted on the construction machine to be reduced.
Effect of the Invention
[0013] The present invention can reduce the particulate matter (PM)
or the nitrogen oxide (NOx) discharged from the internal combustion
engine mounted on the construction machine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a side view showing a general arrangement of a
construction machine according to a first embodiment of the present
invention.
[0015] FIG. 2 is a block diagram showing an arrangement of a drive
system that drives the construction machine according to the first
embodiment of the present invention.
[0016] FIG. 3 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0017] FIG. 4 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0018] FIG. 5 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0019] FIG. 6 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0020] FIG. 7 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0021] FIG. 8 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0022] FIG. 9 is a block diagram showing an arrangement of a drive
system that drives a construction machine according to a second
embodiment of the present invention.
[0023] FIG. 10 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the second embodiment of the present invention.
[0024] FIG. 11 is a set of timing charts showing operations of the
drive system incorporated in the construction machine according to
the second embodiment of the present invention.
MODES FOR CARRYING OUT THE INVENTION
[0025] Arrangements and operations of a construction machine
according to a first embodiment of the present invention will be
described below with reference to FIGS. 1 to 8. The following
description assumes that the construction machine is a hydraulic
excavator as a representative construction machine.
[0026] A general arrangement of the construction machine according
to the first embodiment of the present invention will be described
with reference to FIG. 1.
[0027] FIG. 1 is a side view showing the general arrangement of the
construction machine according to the first embodiment of the
present invention.
[0028] A hydraulic excavator 200 includes a track structure 201 and
a swing structure 202. The track structure 201 has a function of
causing the construction machine to travel with a track hydraulic
motor. The track structure includes a right track structure and a
left track structure, each being driven by an independent track
hydraulic motor. The swing structure 202 is rotated relative to the
track structure 201 by a swing mechanism 113.
[0029] The swing structure 202 includes a boom 203, an arm 204, and
a bucket 205 that perform excavating work, the boom 203, the arm
204, and the bucket 205 being disposed on the other side (e.g., on
the right-hand side, looking to the front) at a front portion of
the swing structure 202. The boom 203, the arm 204, and the bucket
205 are driven by a hydraulic cylinder 107, a hydraulic cylinder
106, and a hydraulic cylinder 105, respectively.
[0030] The swing structure 202 further includes a cab 206. An
operator gets on board the cab 206 and uses an operating lever to
operate the construction machine 200.
[0031] An arrangement of a drive system that drives the
construction machine according to the first embodiment will be
described below with reference to FIG. 2.
[0032] FIG. 2 is a block diagram showing the arrangement of the
drive system that drives the construction machine according to the
first embodiment of the present invention.
[0033] A diesel engine 101 as an internal combustion engine and a
first electric motor 102 are mechanically connected to each other
to thereby drive a hydraulic pump 103 as a hydraulic pressure
generator. It is here noted that, for example, the diesel engine
101, the first electric motor 102, and the hydraulic pump 103 are
mechanically connected so as to run at an identical speed.
Hydraulic fluid sent from the hydraulic pump 103 is distributed by
a control valve 104 based on an operation by the operator and
supplied to the hydraulic cylinders 105, 106 and 107, a left track
hydraulic motor 108, and a right track hydraulic motor 109. The
hydraulic cylinder 105 drives the bucket 205 shown in FIG. 1. The
hydraulic cylinder 106 drives the arm 204 shown in FIG. 1. The
hydraulic cylinder 107 drives the boom 203 shown in FIG. 1. The
left track hydraulic motor 108 and the right track hydraulic motor
109 drive the left track structure and the right track structure,
respectively, of the track structure 201 shown in FIG. 1.
[0034] The first electric motor 102 and a second electric motor 112
that drives the swing mechanism 113 are each a three-phase
synchronous motor and a motor generator. An electric power
converter 110 converts direct current (DC) electric power stored in
an electric energy storage device 111 to three-phase alternating
current (AC) electric power and supplies the three-phase AC
electric power to, and thereby drive, the first electric motor 102
and the second electric motor 112. The first electric motor 102 is
also operated as a generator to charge the electric energy storage
device 111 via the electric power converter 110. The second
electric motor 112 operates as a generator when the swing structure
202 rotating is to be braked, thereby charging the electric energy
storage device 111 via the electric power converter 110.
[0035] A capacitor having a relatively small capacity is used for
the electric energy storage device 111. In this case, a charge
amount of the electric energy storage device 111 needs to be
appropriately controlled.
[0036] A subtractor 120 calculates a difference between a charge
amount command Q* and a charge amount Q of the electric energy
storage device 111. The charge amount command Q* is given by a host
controller and is a predetermined value that corresponds to, for
example, an 80% charge amount of the electric energy storage device
111.
[0037] A charge amount control device 114 calculates and outputs a
torque target so that the difference obtained by the subtractor 120
becomes equal to 0, specifically, the charge amount Q of the
electric energy storage device 111 agrees with the charge amount
command Q*. A torque limiter 115 obtains and outputs a first torque
command T1* that limits a rate of change with time relative to the
torque target output by the charge amount control device 114. If,
for example, the torque target value changes in a step fashion, the
torque target value is made to change gradually, so that the rate
of change with time in the torque target may be limited to a level
below a predetermined value.
[0038] An engine controller 116 controls the diesel engine 101 so
that output torque of the diesel engine 101 becomes equal to the
first torque command T1*. Specifically, the engine controller 116
controls an amount of fuel supplied by a fuel injection valve of
the diesel engine 101 to a combustion chamber of the diesel engine
101 or an EGR recirculation amount.
[0039] A subtractor 117 calculates a difference between a
rotational speed command N* and a rotational speed N of the first
electric motor. The rotational speed command N* is given by a host
controller and is, for example, a predetermined value.
[0040] A speed control device 118 obtains a second torque command
T2* based on the difference calculated by the subtractor 117 so
that the rotational speed command N* agrees with the rotational
speed N of the first electric motor and outputs the second torque
command T2* to the electric power converter 110. The electric power
converter 110 controls so that torque of the first electric motor
102 becomes equal to the second torque command T2*.
[0041] A swing control device 119 obtains a third torque command
T3* based on an operating amount of a swing lever operated by the
operator and outputs the third torque command T3* to the electric
power converter 110 in order to control the second electric motor
112. The electric power converter 110 controls so that torque of
the second electric motor 112 becomes equal to the third torque
command T3*.
[0042] The electric power converter 110 includes first and second
electric power converting portions built therein, the first
electric power converting portion controlling the first electric
motor 102, the second electric power converting portion controlling
the second electric motor 112. For example, the first electric
power converting portion includes a plurality of switching elements
and a control part. The switching elements convert DC electric
power to three-phase AC electric power. The control part performs
PWM control for opening or closing the switching elements so that
current flowing through the first electric motor 102 agrees with a
current command corresponding to the abovementioned second torque
command T2*. The first electric power converting portion thereby
controls so that the torque of the first electric motor 102 becomes
equal to the second torque command T2*. Additionally, when the
first electric motor 102 operates as a generator, the control part
controls the switching elements and converts an output of electric
power generated by the first electric motor 102 to DC electric
power and stores the DC electric power in the electric energy
storage device 111. The second electric power converting portion,
having arrangements and operations identical to those of the first
electric power converting portion, controls so that the torque of
the second electric motor 112 becomes equal to the third torque
command T3*. When the second electric motor 112 operates as a
generator, the control part controls the switching elements and
converts an output of electric power generated by the second
electric motor 112 to DC electric power and stores the DC electric
power in the electric energy storage device 111.
[0043] Operations of the drive system incorporated in the
construction machine according to the first embodiment will be
described below with reference to FIGS. 3 to 8.
[0044] FIGS. 3 to 8 are timing charts showing the operations of the
drive system incorporated in the construction machine according to
the first embodiment of the present invention.
[0045] Operations of different parts of the drive system when, for
example, the arm is operated will first be described below with
reference to FIG. 3.
[0046] The abscissas on FIG. 3 represent elapsed time. The ordinate
on FIG. 3(a) represents pump torque of the hydraulic pump 103 and
the ordinate on FIG. 3(b) represents the rotational speed N of the
first electric motor 102. It is assumed that the diesel engine 101,
the first electric motor 102, and the hydraulic pump 103 are
mechanically connected so as to run at an identical speed. The
ordinate on FIG. 3(c) represents torque of the first electric motor
102 and the ordinate on FIG. 3(d) represents discharge current of
the electric energy storage device 111. The ordinate on FIG. 3(e)
represents the charge amount Q of the electric energy storage
device 111 and the ordinate on FIG. 3(f) represents torque of the
diesel engine 101. FIG. 3 then shows that torque of the hydraulic
pump 103 increases as a result of an operation performed by the
operator at time t1. One of the cases in which the torque of the
hydraulic pump 103 increases as a result of an operation of the
operator is when, for example, the operator operates an operating
lever for the bucket 205 shown in FIG. 1 and the torque of the
hydraulic pump 103 is increased to drive the hydraulic cylinder 105
according to the operation. Other possible cases include when each
one of the boom 203, the arm 204 or the track structure 201 is
driven.
[0047] When the torque of the hydraulic pump 103 is increased at
time t1 as shown in FIG. 3(a), the rotational speed N decreases as
shown in FIG. 3(b) with a resultant increase in the difference from
the rotational speed command N*; this increases the second torque
command T2*, which increases the torque of the first electric motor
102 as shown in FIG. 3(c). This causes the rotational speed N to
start increasing and to recover at time t2 as shown in FIG. 3(b).
Specifically, even with fluctuations in pump torque, the speed
control device 118 controls the torque of the first electric motor
102 and the rotational speed N is maintained at a constant
level.
[0048] When the torque of the first electric motor 102 is increased
at time t1 as shown in FIG. 3(c), the discharge current of the
electric energy storage device 111 increases at time t1 to supply
electric power as shown in FIG. 3(d) and the charge amount Q
decreases as shown in FIG. 3(e). This increases the difference from
the charge amount command Q* calculated by the subtractor 120,
which increases the engine torque target output by the charge
amount control device 114. The torque target is subject to
limitation of the rate of change with time imposed by the torque
limiter 115 and output as the first torque command T1* to the
engine controller 116. FIG. 3(f) shows the diesel engine torque
when the rate of change with time in the first torque command T1*
is limited as described above. Changes in torque after time t1
follow the rate of change with time limited by the torque limiter
115 or lower. This eliminates the likelihood that the diesel engine
101 will change its torque sharply and allows the diesel engine 101
to avoid combustion in a condition of high equivalence ratios due
to excessive fuel injection with which particulate matter tends to
be produced or in a condition of excessive combustion temperatures
at which nitrogen oxide tends to be produced.
[0049] When the torque of the diesel engine 101 increases at time
t2 to time t3 as shown in FIG. 3(f), the torque of the first
electric motor 102 decreases in proportion thereto as shown in FIG.
3(c). This is because of the torque of the first electric motor 102
being controlled so that a sum of the torque of the diesel engine
101 and the torque of the first electric motor 102 balances the
pump torque to thereby keep the rotational speed N constant.
[0050] The control at time t2 to time t3 will be described in
greater detail below. Because the charge amount Q of the electric
energy storage device 111 decreases at time t2, the difference
output by the subtractor 120 increases. Accordingly, the torque
target value output by the charge amount control device 114
increases. The engine controller 116 controls the output torque of
the diesel engine 101 according to the torque target value, which
causes the torque of the diesel engine 101 to increase gradually as
shown in FIG. 3(f). Meanwhile, when the output torque of the diesel
engine 101 increases, the rotational speed of the diesel engine 101
increases and the rotational speed of the first electric motor 101
connected to the diesel engine 101 also increases. As a result, the
speed difference output by the subtractor 117 increases. This
causes the second torque command T2* output by the speed control
device 118 to decrease. The torque of the first electric motor 101,
being controlled by the electric power converter 110 according to
the second torque command T2*, gradually decreases as shown in FIG.
3(c).
[0051] When the torque of the diesel engine 101 exceeds the pump
torque at time t3, the torque of the first electric motor 102
becomes negative, specifically, the first electric motor 102
performs an electric power generating operation and the diesel
engine 101 drives the first electric motor 102 that performs the
electric power generating operation as well as the hydraulic pump
103. In addition, the electric power generated by the first
electric motor 102 is supplied to the electric energy storage
device 111, which causes the charge amount Q to start increasing
toward the charge amount command Q* as shown in FIG. 3(e).
[0052] At time t4, the charge amount Q shown in FIG. 3(e)
substantially agrees with the charge amount command Q*. At this
time, the torque of the first electric motor 102 is 0 as shown in
FIG. 3(c) and the torque of the diesel engine 101 balances the pump
torque with the rotational speed N controlled at the rotational
speed command N*.
[0053] Operations of different parts of the drive system when the
swing structure 202 performs a swing operation will be described
below with reference to FIG. 4. The ordinates on FIGS. 4(a) to 4(f)
represent the same as those on FIGS. 3(a) to 3(f). FIG. 4(g) shows
the output of the second electric motor 112. FIG. 4 shows that the
second electric motor 112 is started by an operation of the swing
lever performed by the operator at time t1, the second electric
motor 112 is braked by an operation of the swing lever performed by
the operator at time t2, and the second electric motor 112 is
brought to a stop at time t4.
[0054] When the second electric motor 112 starts rotating at time
t1, the rotational speed starts increasing, which increases the
output of the second electric motor 112 as shown in FIG. 4(g).
Accordingly, to prevent the charge amount Q of the electric energy
storage device 111 from being decreased due to an increase in the
discharge current of the electric energy storage device 111, the
torque target output by the charge amount control device 114
increases. This increases the torque of the diesel engine 101 as
shown in FIG. 4(f). Meanwhile, to prevent the rotational speed N
from increasing due to the increase in the torque of the diesel
engine 101, the speed control device 118 decreases the second
torque command T2*. This makes the torque of the first electric
motor 102 negative as shown in FIG. 4(c). The first electric motor
102 then performs the electric power generating operation and the
discharge current of the electric energy storage device 111 is
prevented from increasing, so that the charge amount Q can be
prevented from decreasing. Specifically, the torque of the diesel
engine 101 increases in proportion to the output of the second
electric motor 112. The first electric motor 102 then generates
electric power with the increased torque, so that the rotational
speed N and the charge amount Q are controlled so as to agree with
the rotational speed command N* and the charge amount command Q*,
respectively. It is noted that the rate of change with time in the
torque target associated with the increase in the output of the
second electric motor 112 at this time is equal to, or lower than,
the limited value and the first torque command T1* agrees with the
torque target.
[0055] Through the foregoing control, at time t1 to time t2, the
torque of the diesel engine 101 increases as shown in FIG. 4(f) and
the torque of the first electric motor 102 decreases (the amount of
electric power generated increases) as shown in FIG. 4(c), in
proportion to the increase in the output of the second electric
motor 112 as shown in FIG. 4(g).
[0056] When deceleration of the second electric motor 112 is
started at time t2, the output suddenly changes from powering to
regeneration. The output of the second electric motor 112 undergoes
a sudden change from positive to negative as shown in FIG. 4(g).
Accordingly, in order to absorb electric power regenerated by the
second electric motor 112 and electric power generated by the first
electric motor 102, the discharge current of the electric energy
storage device 111 is decreased as shown in FIG. 4(d),
specifically, charging of the electric energy storage device 111 is
started as shown in FIG. 4(e) to increase the charge amount Q. As
the charge amount Q increases, the torque target is decreased by
the charge amount control device 114. At this time, the torque
target tends to change sharply because of the precipitous change in
the output of the second electric motor 112; however, because of
the rate of change in the first torque command T1* being limited by
the torque limiter 115, the torque of the diesel engine 101 does
not change precipitously, as shown in FIG. 4(f).
[0057] This prevents the diesel engine 101 from changing its torque
precipitously and allows the diesel engine 101 to avoid combustion
in a condition of high equivalence ratios due to excessive fuel
injection with which particulate matter tends to be produced or in
a condition of excessive combustion temperatures at which nitrogen
oxide tends to be produced.
[0058] The torque of the first electric motor 102 with its
rotational speed N controlled at a constant level increases with
the deceasing torque of the diesel engine 101 as shown in FIG. 4(c)
and the amount of electric power generated by the first electric
motor 102 decreases slowly. Thus, the charge amount Q continues to
increase for some while.
[0059] The torque of the first electric motor 102 continues to
increase and the first electric motor 102 shifts from an electric
power generating state to a powering state. Then, when power
consumption exceeds the electric power regenerated by the second
electric motor 112 at time t3, the charge amount Q starts
decreasing as shown in FIG. 4(e). When the charge amount Q
decreases, the torque target is increased by the charge amount
control device 114 and, as shown in FIG. 4(f), the torque of the
diesel engine 101 increases. To prevent the rotational speed N from
increasing due to the increase in the torque of the diesel engine
101, the speed control device 118 decreases the torque of the first
electric motor 102 and the discharge current of the electric energy
storage device 111 decreases as shown in FIG. 4(c).
[0060] As a result, the following conditions develop at time t5:
specifically, the torque of the first electric motor 102 is 0 as
shown in FIG. 4(c), the discharge current of the electric energy
storage device 111 is 0 as shown in FIG. 4(d), the charge amount Q
agrees with the charge amount command Q* as shown in FIG. 4(e), and
the torque of the diesel engine 101 agrees with the pump
torque.
[0061] As described above, even when the second electric motor 112
performs powering and regenerative operations as a result of a
swing operation, the rotational speed N is controlled so as to
agree with the rotational speed command N*, the rate of change with
time in the torque of the diesel engine 101 can be limited, and the
charge amount Q of the electric energy storage device 111 is
controlled so as to agree with the charge amount command Q*.
[0062] Changes with time of the pump torque, the rotational speed
N, the torque of the first electric motor 102, and the torque of
the diesel engine 101 when the rate of change with time in the pump
torque is changed will be described below with reference to FIGS. 5
to 8.
[0063] FIGS. 5 to 8 are each concerned with a specific condition of
the rate of change with time in the pump torque, the conditions
being labeled as condition 1 to condition 4. Conditions 1 and 2
show cases with low rates of change with time in the pump torque
and conditions 3 and 4 show cases with high rates of change with
time in the pump torque. Conditions 2 and 4 are concerned with
rates of change with time in the pump torque twice as high as those
of conditions 1 and 3, respectively.
[0064] The abscissas on FIGS. 5 to 8 represent time. The ordinate
on FIG. 5(a) represents the pump torque of the hydraulic pump 103
and the ordinate on FIG. 5(b) represents the rotational speed N of
the first electric motor 102. It is assumed that the diesel engine
101, the first electric motor 102, and the hydraulic pump 103 are
mechanically connected so as to run at an identical speed. The
ordinate on FIG. 5(c) represents the torque of the first electric
motor 102 and the ordinate on FIG. 5(f) represents the torque of
the diesel engine 101. The broad dotted line on FIG. 5(f) is a
reference line that serves as a guide easily determining an
inclination of a torque line. The ordinates on FIGS. 6(a) to 6(c)
and 6(f) to FIGS. 8(a) to 8(c) and 8(f) represent the same as those
represented by the ordinates on FIGS. 5(a) to 5(c) and 5(f).
[0065] In condition 1 (FIG. 5) and condition 2 (FIG. 6), because of
the low rates of change with time in the pump torque as shown in
FIGS. 5(a) and 6(a), the torque of the diesel engine 101 can follow
the increase in the pump torque as shown in FIGS. 5(f) and 6(f).
This eliminates the need for making the torque of the first
electric motor 102 large and, as shown in FIGS. 5(c) and 6(c) and
the torque of the first electric motor 102 is smaller than the
torque of the diesel engine 101 at the peak of the torque of the
first electric motor 102.
[0066] In contrast, in condition 3 (FIG. 7) and condition 4 (FIG.
8), because of the high rates of change with time in the pump
torque as shown in FIGS. 7(a) and 8(a), the torque of the diesel
engine 101 cannot follow the increase in the pump torque. To
maintain the rotational speed N, the torque of the first electric
motor 102 needs to be made large as shown in FIGS. 7(c) and 8(c)
and becomes larger than the torque of the diesel engine 101 at the
peak of the torque of the first electric motor 102.
[0067] Attention is now focused on the rate of change with time in
the pump torque of the diesel engine 101 when the rate of change
with time in the pump torque changes from condition 1 to condition
2 in conditions 1 and 2 having the low rates of change with time in
the pump torque. The rate of change with time in the torque of the
diesel engine 101 in condition 2 (FIG. 6) changes greatly relative
to that in condition 1 (FIG. 5). In contrast, in conditions 3 and 4
having the low rates of change with time in the pump torque,
because of the limitation imposed by the torque limiter 115, the
rate of change with time in the torque of the diesel engine 101 in
condition 4 (FIG. 8) changes a little relative to that in condition
3 (FIG. 7) when the rate of change with time in the pump torque
changes from condition 3 to condition 4. Specifically, when the
rates of change with time in the pump torque are low (conditions 1
and 2), the increase in the rate of change with time in the torque
of the diesel engine 101 relative to the increase in the rate of
change with time in the pump torque is high; and when the rates of
change with time in the pump torque are high (conditions 3 and 4),
the increase in the rate of change with time in the torque of the
diesel engine 101 relative to the increase in the rate of change
with time in the pump torque is low.
[0068] In either case, because of the functioning of the speed
control device 116, the rotational speed N is controlled so as to
agree with the rotational speed command N*. Specifically, in the
construction machine according to the first embodiment, the torque
of the diesel engine 101 is controlled according to the pump torque
when the rate of change with time in the pump torque is low;
because the rate of change with time in the torque of the diesel
engine 101 is low at this time, the diesel engine 101 does not
develop a condition in which particulate matter and nitrogen oxide
tend to be produced.
[0069] In contrast, when the rate of change with time in the pump
torque is high, the rate of change with time in the torque of the
diesel engine 101 is limited and is not controlled according to the
pump torque. Thus, in this case, too, the rate of change with time
in the torque of the diesel engine 101 is limited, so that the
diesel engine 101 does not develop a condition in which particulate
matter and nitrogen oxide tend to be produced.
[0070] As described heretofore, in the first embodiment, the
particulate matter (PM) or the nitrogen oxide (NOx) discharged from
the internal combustion engine mounted on the construction machine
can be reduced and the charge amount of the electric energy storage
device that supplies electric power to the electric motor can be
appropriately controlled.
[0071] Additionally, the charge amount of a capacitor having a
small capacity, if used for the electric energy storage device, can
also be appropriately controlled.
[0072] Arrangements and operations of a construction machine
according to a second embodiment of the present invention will be
described below with reference to FIGS. 9 to 11. A hydraulic
excavator as the construction machine according to the second
embodiment has a general arrangement identical to that shown in
FIG. 1.
[0073] An arrangement of a drive system that drives the
construction machine according to the second embodiment will be
described below with reference to FIG. 9.
[0074] FIG. 9 is a block diagram showing the arrangement of the
drive system that drives the construction machine according to the
second embodiment of the present invention. Like or equal parts are
identified by the same reference numerals as those used in FIG.
2.
[0075] Based on a difference between a rotational speed command N*
and a rotational speed N' of a diesel engine 101 obtained by a
subtractor 130, a second speed control device 131 calculates a
torque target such that the rotational speed N' of the diesel
engine 101 agrees with the rotational speed command N*. The second
speed control device 131 then outputs the torque target to a torque
limiter 115.
[0076] A high-pass filter 132 produces an output of a speed control
device 118 from which a low-frequency component including a DC
component is removed. A subtractor 133 subtracts an output of a
charge amount control device 114 from the output of the high-pass
filter 132 representing the output of the speed control device 118
from which the low-frequency component including the DC component
is removed. The subtractor 133 then outputs the result as a second
torque command T2*.
[0077] It is noted that the diesel engine 101 and a first electric
motor 102 are mechanically connected to each other and thus run at
an identical speed that will hereinafter be represented by a
rotational speed N.
[0078] Operations of the drive system according to the second
embodiment will be described below.
[0079] When torque of a hydraulic pump 103 changes, the second
speed control device 131 limits fluctuations in the rotational
speed N; still, the torque limiter 115 limits the rate of change in
torque of the diesel engine 101. This prevents the diesel engine
101 from developing a condition in which particulate matter or
nitrogen oxide tends to be produced. Meanwhile, because of the rate
of change in the torque of the diesel engine 101 being limited, it
is difficult to sufficiently limit the fluctuations in the
rotational speed N only with the second speed control device 131.
Thus, the fluctuations in the rotational speed N is limited
transiently by the speed control device 118. In addition, because
the low-frequency component is removed by the high-pass filter 132
in a steady state, control of the charge amount Q by the charge
amount control device 114 is performed.
[0080] Operations of the drive system incorporated in the
construction machine according to the second embodiment will be
described below with reference to FIGS. 10 to 11.
[0081] FIGS. 10 and 11 are timing charts showing operations of the
drive system incorporated in the construction machine according to
the second embodiment of the present invention.
[0082] FIG. 10 shows operations of different parts of the drive
system when, for example, the arm is operated and the pump torque
is changed. The operations are the same as those described with
reference to FIG. 3.
[0083] In this case, the rotational speed N is controlled so as to
agree with the rotational speed command N*, the rate of change with
time in the torque of the diesel engine 101 is limited, and the
charge amount Q of an electric energy storage device 111 is
controlled so as to agree with the charge amount command Q*.
[0084] FIG. 11 shows operations of different parts of the drive
system when a second electric motor 112 is operated. The operations
are the same as those described with reference to FIG. 4.
[0085] In this case, the rotational speed N is controlled so as to
agree with the rotational speed command N*, the rate of change with
time in the torque of the diesel engine 101 is limited, and the
charge amount Q of the electric energy storage device 111 is
controlled so as to agree with the charge amount command Q*.
[0086] As described heretofore, in the second embodiment, too, the
particulate matter (PM) or the nitrogen oxide (NOx) discharged from
the internal combustion engine mounted on the construction machine
can be reduced and the charge amount of the electric energy storage
device that supplies electric power to the electric motor can be
appropriately controlled.
[0087] Additionally, the charge amount of a capacitor having a
small capacity, if used for the electric energy storage device, can
also be appropriately controlled.
[0088] In the above-described embodiments, a predetermined constant
value is given as the rotational speed command N*. The rotational
speed command N* may, however, be decreased for a light hydraulic
pump load or increased for a heavy hydraulic pump load. Varying the
rotational speed command N* in this manner still allows the
rotational speed N to follow the rotational speed command N*
because of the control performed based on the difference
therebetween.
[0089] The rate of change with time of the torque limiter 105,
while it has been described to be constant, may still be varied
depending on the operating condition of the diesel engine 101
within a range in which the particulate matter or the nitrogen
oxide does not increase to a level more than a predetermined
amount. Additionally, an input to, and an output from, the torque
limiter 105 are made to agree with each other such that the
particulate matter or the nitrogen oxide does not increase to a
level more than a predetermined amount and the torque limiter 105
may be configured so as to limit the rate of change with time in
the output if the particulate matter or the nitrogen oxide
increases to a level more than the predetermined amount with the
input made to agree with the output.
[0090] Additionally, the diesel engine 101, the first electric
motor 102, and the hydraulic pump 103 are mechanically connected so
as to run at an identical speed. The connection may nonetheless be
achieved via a transmission, in which case, the rotational speed
command N*, the rotational speed N', and the rotational speed N
need to be converted in consideration of a gear ratio.
DESCRIPTION OF REFERENCE NUMERALS
[0091] 101 Diesel engine (internal combustion engine) [0092] 102
First electric motor [0093] 103 Hydraulic pump (hydraulic pressure
generator) [0094] 104 Control valve [0095] 105, 106, 107 Hydraulic
cylinder [0096] 108, 109 Hydraulic motor [0097] 110 Electric power
converter [0098] 111 Electric energy storage device [0099] 112
Second electric motor [0100] 113 Swing mechanism [0101] 114 Charge
amount control device [0102] 115 Torque limiter (second control
means) [0103] 116 Engine controller [0104] 118 Speed control device
(first control means) [0105] 119 Swing control device [0106] 131
Second speed control device [0107] 132 High-pass filter [0108] 200
Hydraulic excavator (exemplary construction machine)
* * * * *