U.S. patent application number 14/122250 was filed with the patent office on 2014-07-03 for construction machine.
This patent application is currently assigned to HITACHI CONSTRUCTION MACHINERY CO., LTD.. The applicant listed for this patent is Yuichiro Morita, Takashi Ogawa, Kohei Sakurai. Invention is credited to Yuichiro Morita, Takashi Ogawa, Kohei Sakurai.
Application Number | 20140184122 14/122250 |
Document ID | / |
Family ID | 47295979 |
Filed Date | 2014-07-03 |
United States Patent
Application |
20140184122 |
Kind Code |
A1 |
Ogawa; Takashi ; et
al. |
July 3, 2014 |
CONSTRUCTION MACHINE
Abstract
A construction machine includes: a swing structure (1d); an
electric motor (16) that drives the swing structure; an operating
device (4b) that outputs an operating signal according to an
operating amount and an operating direction; an inverter device
(13) that controls the electric motor based on a control signal
generated based on the operating signal; a position sensor (24)
that detects an actual speed of the electric motor; and a second
controller (22) that determines whether at least one of a first
condition and a second condition is satisfied. The first condition
is satisfied when a sign of a value computed by subtracting the
actual speed V from a target speed V* of the electric motor that
defined by the control signal; and the second condition is
satisfied when a difference between the target speed and the actual
speed is greater than a reference value Vth, and when the
acceleration is greater than a reference value .beta.th. This
prevents erroneous determination and failure of detection relating
to determination of faults in an electronic control system from
occurring.
Inventors: |
Ogawa; Takashi; (Tokyo,
JP) ; Sakurai; Kohei; (Tokyo, JP) ; Morita;
Yuichiro; (Hitachi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ogawa; Takashi
Sakurai; Kohei
Morita; Yuichiro |
Tokyo
Tokyo
Hitachi |
|
JP
JP
JP |
|
|
Assignee: |
HITACHI CONSTRUCTION MACHINERY CO.,
LTD.
Tokyo
JP
|
Family ID: |
47295979 |
Appl. No.: |
14/122250 |
Filed: |
May 30, 2012 |
PCT Filed: |
May 30, 2012 |
PCT NO: |
PCT/JP2012/063989 |
371 Date: |
November 26, 2013 |
Current U.S.
Class: |
318/461 ;
318/490 |
Current CPC
Class: |
H02P 3/18 20130101; H02P
3/04 20130101; H02P 6/06 20130101; E02F 9/128 20130101; B60L
2200/40 20130101; Y02T 10/642 20130101; G01P 3/44 20130101; E02F
9/2095 20130101; E02F 9/267 20130101; H02P 6/12 20130101; Y02T
10/64 20130101; H02P 29/0241 20160201 |
Class at
Publication: |
318/461 ;
318/490 |
International
Class: |
H02P 3/04 20060101
H02P003/04; G01P 3/44 20060101 G01P003/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 2011 |
JP |
2011-130630 |
Claims
1. A construction machine comprising: a swing structure; an
electric motor that drives the swing structure; an operating device
that outputs an operating signal for operating the electric motor
according to an operating amount and an operating direction; first
control means that controls the electric motor based on a control
signal generated based on the operating signal; detecting means
that detects an actual speed of the electric motor; and second
control means that determines whether at least one of a first
condition and a second condition is satisfied, the first condition
that is satisfied when a sign of a value computed by subtracting
the actual speed from a target speed of the electric motor, the
target speed defined by the control signal, is different from a
sign of acceleration of the electric motor, and the second
condition that is satisfied when a difference value between the
target speed and the actual speed is greater than a first reference
value and when the acceleration is greater than a second reference
value.
2. The construction machine according to claim 1, further
comprising: a braking device that brakes the electric motor based
on a braking signal, wherein the second control means outputs the
braking signal to the braking device when at least one of the first
condition and the second condition is satisfied.
3. The construction machine according to claim 1, further
comprising: an annunciating device that annunciates occurrence of a
fault in the construction machine based on an annunciation signal,
wherein the second control means outputs the annunciation signal to
the annunciating device when at least one of the first condition
and the second condition is satisfied.
4. The construction machine according to claim 1, further
comprising: acceleration detecting means that detects acceleration
of the electric motor.
5. The construction machine according to claim 1, wherein the
acceleration of the electric motor is calculated based on target
torque of the electric motor defined by the control signal or
actual torque generated by the electric motor.
6. The construction machine according to claim 1, wherein the first
control means differs from the second control means.
Description
TECHNICAL FIELD
[0001] The present invention relates to a construction machine
including an electric motor for driving a swing structure.
BACKGROUND ART
[0002] In recent years, more and more construction machines are
electrified with the aim of, for example, improved engine fuel
efficiency and reduced amounts of exhaust gases based on the
techniques relating to hydraulic excavators. Examples of such
construction machines include a hybrid construction machine that
incorporates both a hydraulic actuator and an electric motor as
actuators for driving different parts of the machine, in addition
to an engine and an electric motor (a generator motor) as prime
movers for a hydraulic pump. A known hybrid construction machine
drives hydraulic actuators (hydraulic cylinders and hydraulic
motors) to cause a work implement to perform work and a track
structure to perform a traveling operation. It also drives an
electric motor to cause a swing structure (e.g., an upper swing
structure in a hydraulic excavator) to perform a swing
operation.
[0003] The hybrid construction machine of the foregoing type may
use a controller (e.g., an inverter device) for controlling the
electric motor to achieve intended swing control by converting an
operation amount of a swing operating lever operated by an operator
to a corresponding electric signal and applying the electric signal
to the controller. A fault that may occur in an electronic control
system that includes a sensor for detecting a state of the electric
motor (e.g., a magnetic pole position sensor of the electric
motor), the controller, and the electric motor in a series of
control processes, however, hampers correct swing control,
resulting in a swing operation not intended by the operator being
performed.
[0004] A known technique for avoiding such a situation as that
described above uses a controller that monitors a difference
between a speed command of an electric motor (a target speed)
generated based on the operation amount of the swing operating
lever and an actual speed of the electric motor and determines the
operation to be a faulty operation when the difference falls
outside a permissible range (see JP-A-2007-228721).
PRIOR ART DOCUMENT
Patent Document
[0005] Patent Document 1: JP-2007-228721-A
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
[0006] In a construction machine including a swing structure that
has a large inertia, however, the speed command often differs
widely from the actual speed. Use of only the magnitude of the
difference between the speed command and the actual speed to
determine whether a faulty operation occurs, as in the
abovementioned related art, can cause inconveniences. Specifically,
if the permissible range of the difference is set to be excessively
small, a normal operation may be erroneously determined to be a
faulty one, which may reduce work efficiency. By contrast, with a
permissible range set to be excessively large, the controller can
fail to detect a faulty operation, resulting in reduced
reliability.
[0007] The present invention has been made in view of the foregoing
situation and it is an object of the present invention to provide a
construction machine that can prevent erroneous determination and
failure of detection relating to determination of faults in an
electronic control system.
Means for Solving the Problem
[0008] To achieve the foregoing object, an aspect of the present
invention provides a construction machine comprising: a swing
structure; an electric motor that drives the swing structure; an
operating device that outputs an operating signal for operating the
electric motor according to an operating amount and an operating
direction; first control means that controls the electric motor
based on a control signal generated based on the operating signal;
detecting means that detects an actual speed of the electric motor;
and second control means that determines whether at least one of a
first condition and a second condition is satisfied, the first
condition that is satisfied when a sign of a value computed by
subtracting the actual speed from a target speed of the electric
motor, the target speed defined by the control signal, is different
from a sign of acceleration of the electric motor, and the second
condition that is satisfied when a difference value between the
target speed and the actual speed is greater than a first reference
value and when the acceleration is greater than a second reference
value.
Effects of the Invention
[0009] In the aspect of the present invention, erroneous
determination and failure of detection relating to determination of
faults in an electronic control system can be prevented and thus
work efficiency and reliability can be enhanced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an illustration showing an appearance of a hybrid
hydraulic excavator including a construction machine control system
according to an embodiment of the present invention.
[0011] FIG. 2 is a configuration diagram showing the construction
machine control system according to the embodiment of the present
invention.
[0012] FIG. 3 is a diagram showing an exemplary application of the
construction machine control system according to the embodiment of
the present invention to a specific construction machine.
[0013] FIG. 4 is a schematic diagram showing a hardware
configuration of an inverter device 13 and its surrounding
components according to the embodiment of the present
invention.
[0014] FIG. 5 is a functional block diagram showing a main
microprocessor 31 according to the embodiment of the present
invention.
[0015] FIG. 6 is a block diagram showing a fault determining unit
65 according to the embodiment of the present invention.
[0016] FIG. 7A is a graph showing an exemplary relation between a
speed command V* and an actual speed V.
[0017] FIG. 7B is a graph showing an exemplary relation between the
speed command V* and the speed V.
[0018] FIG. 7C is a graph showing an exemplary relation between the
speed command V* and the actual speed V.
[0019] FIG. 7D is a graph showing an exemplary relation between the
speed command V* and the actual speed V.
MODES FOR CARRYING OUT THE INVENTION
[0020] An embodiment of the present invention will be described
below with reference to the accompanying drawings. It is noted that
a first controller, a second controller, a first hydraulic sensor,
and a second hydraulic sensor to be described hereunder may be
denoted by controller 1, controller 2, hydraulic sensor 1, and
hydraulic sensor 2, respectively, in the drawings.
[0021] FIG. 1 is an illustration showing an appearance of a hybrid
hydraulic excavator including a construction machine control system
according to the embodiment of the present invention. This
hydraulic excavator shown in the figure includes an articulated
work implement 1A and a vehicle body 1B. The work implement 1A
includes a boom 1a, an arm 1b, and a bucket 1c. The vehicle body 1B
includes an upper swing structure 1d and a lower track structure
1e.
[0022] The boom 1a is rotatably supported by the upper swing
structure 1d and driven by a hydraulic cylinder (boom cylinder) 3a.
The arm 1b is rotatably supported by the boom 1a and driven by a
hydraulic cylinder (arm cylinder) 3b. The bucket 1c is rotatably
supported by the arm 1b and driven by a hydraulic cylinder (bucket
cylinder) 3c. The upper swing structure 1d is swingably driven by
an electric motor (swing motor) 16 (see FIG. 3). The lower track
structure 1e is driven by left and right track motors (hydraulic
motors) 3e and 3f (see FIG. 3). The hydraulic cylinder 3a, the
hydraulic cylinder 3b, the hydraulic cylinder 3c, and the electric
motor 16 are controlled for driving by operating devices 4a and 4b
(see FIG. 3) disposed in a cab of the upper swing structure 1d, the
operating devices 4a, 4b outputting hydraulic operating
signals.
[0023] FIG. 2 is a configuration diagram showing the construction
machine control system according to the embodiment of the present
invention. The system shown in the figure includes the electric
motor 16, a position sensor (e.g., magnetic pole position sensor)
24, the operating device (swing operating lever) 4b, a first
hydraulic sensor 20, a second hydraulic sensor 21, a first
controller 11, an inverter device (electric power conversion
device) 13, and a swing emergency brake 25. Specifically, the
electric motor 16 drives the upper swing structure ld. The position
sensor 24 detects a rotational position of the electric motor 16.
The operating device 4b outputs a hydraulic operating signal (pilot
pressure) for a swing motion of the upper swing structure ld
according to an amount through which the operating device 4b is
operated (operating amount) and a direction in which the operating
device 4b is operated (operating direction). The first hydraulic
sensor 20 and the second hydraulic sensor 21 each detect pressure
corresponding to the hydraulic operating signal output from the
operating device 4b and output an electric operating signal
corresponding to the pressure. The first controller 11 calculates a
target speed V* of the electric motor 16 based on the electric
operating signal output from the first hydraulic sensor 20 and an
actual speed V (that may be calculated, for example, from the
rotational position detected by the position sensor 24) of the
electric motor 16 and outputs a control signal (speed command)
according to the target speed V*. The inverter device 13 controls
the electric motor 16 based on the control signal (speed command)
output from the first controller 11. The swing emergency brake 25
brakes the upper swing structure ld based on a braking signal
output from the first controller 11 or the inverter device 13.
[0024] The inverter device (electric power conversion device) 13 is
connected to an electric energy storage device (see FIG. 3), such
as a battery. Converting direct current (DC) power charged in the
electric energy storage device 15 into alternating current (AC)
power (three-phase AC) through switching, the inverter device 13
supplies the AC power to the electric motor 16 to thereby control
the electric motor 16. The inverter device 13 includes an inverter
circuit, a driver circuit, and a second controller (control
circuit) 22. The inverter circuit includes a switching device
(e.g., an insulated gate bipolar transistor (IGBT)). The driver
circuit controls driving of the inverter circuit. The second
controller 22 outputs a control signal (torque command) to the
driver circuit to thereby control to turn on and off the switching
device in the inverter circuit. It is noted that, in the
accompanying drawings, the inverter circuit and the driver
circuit-in the inverter device 13 are denoted by "IGBT" as an
exemplary switching device. Thus, in the following, IGBT 23
represents both the inverter circuit and the driver circuit.
[0025] The first hydraulic sensor 20 and the second hydraulic
sensor 21 may be each configured as a set of two hydraulic sensors
for individually detecting a clockwise swing and a counterclockwise
swing of the upper swing structure id as will be described later.
FIG. 2, however, simply shows one hydraulic sensor each. In
addition, in the embodiment, the pilot pressure (hydraulic
operating signal) output from the operating device 4b is detected
by the first hydraulic sensors 20 and 21 for conversion into a
corresponding electric signal. An arrangement may nonetheless be
made in which the electric operating signal according to the
operating direction and the operating amount of the operating
device 4b is directly output. In this case, a position sensor that
detects rotational displacement of the operating lever in the
operating device 4b (e.g., a rotary encoder) may be used.
Additionally, in the embodiment, the operating device 4b has two
hydraulic sensors 20 and 21. Sensors operating on different
detection schemes may nonetheless be combined together; for
example, a combination of the hydraulic sensor and the position
sensor. This can enhance reliability of the system.
[0026] The electric operating signal output from the first
hydraulic sensor 20 is applied to the first controller 11. The
electric operating signal output from the second hydraulic sensor
21 is applied to the second controller 22 disposed in the inverter
device 13.
[0027] The first controller 11 calculates the target speed V* of
the electric motor 16 based on the electric operating signal output
from the first hydraulic sensor 20 and the actual rotational speed
(actual speed V) of the electric motor 16 applied via the second
controller 22. The first controller 11 then outputs a control
signal (speed command) corresponding to the target speed V* to the
second controller 22.
[0028] The second controller 22 outputs a torque command (control
signal) generated in consideration of the speed command (control
signal) applied thereto from the first controller 11, a torque
limit defined by, for example, device performance restrictions
(e.g., pressing force, electricity, DC line voltage), the
rotational position (actual speed V) of the electric motor 16
detected by the position sensor 24, and a current value (actual
current) detected by a three-phase motor current sensor 30. The
second controller 22 then turns on or off the IGBT 23 based on the
torque command, thereby controlling the electric motor 16 (see FIG.
5). Additionally, the second controller 22 calculates the actual
speed V of the electric motor 16 using the rotational position of
the electric motor 16 detected by the position sensor 24 and
outputs the calculated actual speed V (produces a feedback output)
to the first controller 11.
[0029] It is noted that, in the embodiment, the speed command is
output as a command value from the first controller 11; however, a
swing torque command may be used instead. In this case, the second
controller 22 is produce a feedback output of the actual torque
value of the electric motor 16 to the first controller 11.
[0030] A hydraulic brake may, for example, be used for the swing
emergency brake (braking device) 25. The hydraulic brake includes a
plurality of discs pressed by brake shoe springs. The brake is
released when hydraulic pressure for releasing the brake is applied
and the hydraulic pressure overcomes a force of the springs.
[0031] FIG. 3 is a diagram showing an exemplary application of the
construction machine control system according to the embodiment of
the present invention to a specific construction machine. In FIG.
3, like or corresponding parts are identified by the same reference
numerals as used in the preceding figures and descriptions for
those parts may not be duplicated (this applies to each of the
subsequent figures).
[0032] In FIG. 3, the operating devices 4a and 4b each include an
operating lever and generate a pilot pressure according to the
operating direction and the operating amount of the operating lever
operated by an operator. The pilot pressure is generated by a
primary pressure generated in a pilot pump (not shown) being
reduced to a secondary pressure according to the operating amount
of the operating devices 4a and 4b. The pilot pressure defined
according to the operating amount of the operating device 4a is
sent to a pressure receiving part of each of spool type directional
control valves 5a to 5f. This causes the directional control valves
5a to 5f to change their positions from the neutral positions shown
in the figure. The directional control valves 5a to 5f change the
direction of flow of hydraulic fluid generated from a hydraulic
pump 6 powered by an engine 7 to thereby control driving of
hydraulic actuators 3a to 3f. Should pressure inside a hydraulic
line rise inordinately, the hydraulic fluid is released to a tank 9
via a relief valve 8. The hydraulic actuators 3a to 3c serve as the
hydraulic cylinders that drive the boom 1a, the arm 1b, and the
bucket 1c, respectively. The hydraulic actuators 3e and 3f serve as
hydraulic motors that drive the left and right track devices
disposed at the lower track structure 1e.
[0033] A driving power conversion machine (generator motor) 10 is
connected between the hydraulic pump 6 and the engine 7. The
driving power conversion machine 10 functions as both a generator
and a motor. As the generator, the driving power conversion machine
10 converts driving power of the engine 7 to electric energy and
outputs the electric energy to inverter devices 12 and 13. As the
motor, the driving power conversion machine 10 uses electric energy
supplied from the electric energy storage device 15 to assist in
driving the hydraulic pump 6. The inverter device 12 converts
electric energy of the electric energy storage device 15 to AC
electric power and supplies the AC electric power to the driving
power conversion machine 10 to assist in driving the hydraulic pump
6.
[0034] The inverter device 13 supplies electric power output from
the driving power conversion machine 10 or the electric energy
storage device 15 to the electric motor 16 and corresponds to the
inverter device 13 shown in FIG. 2. Thus, the inverter device 13
includes the second controller 22 shown in FIG. 2. With an input of
a speed command (control signal) received from the first controller
11, the inverter device 13 controls driving of the electric motor
16. The inverter device 13 also determines whether a fault occurs
in an electronic control system (the electric motor 16, the
position sensor 24, and the inverter device 13) relating to the
electric motor 16 based on the target speed V* defined by the speed
command output from the first controller 11, the actual speed V of
the electric motor 16 calculated from a detected value of the
position sensor 24, and acceleration dV/dt that is a change with
time of the actual speed V of the electric motor 16. The second
hydraulic sensors 21 (21a, 21b) are disposed in, out of pilot lines
connecting between the operating devices 4a and 4b and the
directional control valves 5a to 5f, two pilot lines that control
swing motions of the upper swing structure id in clockwise and
counterclockwise directions.
[0035] A chopper 14 controls voltage of a DC electric power line
L1. The electric energy storage device 15 supplies electric power
to the inverter devices 12 and 13 via the chopper 14 and stores
electric energy generated by the driving power conversion machine
10 and electric energy regenerated from the electric motor 16. A
capacitor, a battery, or both may be used for the electric energy
storage device 15.
[0036] The first controller 11 calculates the target speed V* of
the electric motor 16 based on electric operating signals input
from the first hydraulic sensors 20 (20a, 20b) connected,
respectively, to, out of the pilot lines connecting between the
operating devices 4a and 4b and the directional control valves 5a
to 5f, two pilot lines that control the swing motions of the upper
swing structure 1d in the clockwise and counterclockwise
directions. The first controller 11 then outputs a control signal
(swing operating command) according to the calculated target speed
V* to the inverter device 13. Additionally, the first controller 11
performs driving power regenerative control that recovers electric
energy from the electric motor 16 during swing braking.
Furthermore, during the driving power regenerative control and when
excess electric power is produced under light hydraulic load, the
first controller 11 performs control to store the recovered
electric power and excess electric power in the electric energy
storage device 15.
[0037] The inverter devices 12, 13, the chopper 14, and the first
controller 11 transmit and receive signals required for the control
via a communication line L2.
[0038] FIG. 4 is a schematic diagram showing a hardware
configuration of the inverter device 13 and its surrounding
components according to the embodiment of the present invention. As
shown in FIG. 4, the second controller 22 includes a main
microprocessor (first microprocessor) 31 and a monitoring
microprocessor (second microprocessor) 32 as control units. The
main microprocessor 31 and the monitoring microprocessor 32 are
control units independent of each other. Communication drivers 33a
and 33b are connected to the main microprocessor 31 and the
monitoring microprocessor 32, respectively, each assuming an
interface between the corresponding microprocessor 31 or 32 and the
communication line L2.
[0039] The main microprocessor 31 receives inputs of a speed
command input from the first controller 11 via the communication
driver 33a, an electric operating signal output from the second
hydraulic sensor 21, rotational position information of the
electric motor 16 output from the position sensor 24, and actual
current information output from the current sensor 30. Using the
information from the position sensor 24 and the current sensor 30,
the main microprocessor 31 outputs a gate control signal to the
IGBT 23 so as to satisfy the speed command input from the first
controller 11 by way of the communication line L2.
[0040] The monitoring microprocessor 32 receives inputs of a speed
command input from the first controller 11 via the communication
driver 33b, an electric operating signal output from the second
hydraulic sensor 21, rotational position information of the
electric motor 16 output from the position sensor 24, and current
information output from the current sensor 30. The monitoring
microprocessor 32 performs a process of determining whether a fault
exists in the electronic control system relating to the electric
motor 16 based on the target speed V* of the electric motor 16
defined by the speed command, the actual speed V of the electric
motor 16 calculated from the rotational position information from
the position sensor 24, and the acceleration dV/dt that is a change
with time of the actual speed V of the electric motor 16.
[0041] FIG. 5 is a functional block diagram showing the main
microprocessor 31 according to the embodiment of the present
invention. As shown in FIG. 5, the main microprocessor 31 includes
a speed control unit 60, a torque control unit 61, a PWM control
unit 62, a speed calculating unit 64, and a fault determining unit
65. The main microprocessor 31 controls the speed of the electric
motor 16 through feedback control.
[0042] The speed control unit 60 generates a torque command
intended for the torque control unit 61 so that the actual speed V
calculated by the speed calculating unit 64 follows the speed
command (target speed V*).
[0043] The torque control unit 61 generates a voltage command so
that actual torque follows the torque command generated by the
speed control unit 60. In addition, if the electric motor 16 cannot
be made to follow the torque command output from the speed control
unit 60 due to, for example, device performance restrictions
relating to the hydraulic excavator, the torque control unit 61
limits the torque command (specifically, reduces as necessary the
torque command output from the speed control unit 60).
[0044] The PWM control unit 62 generates a gate control signal
through pulse width modulation (PWM).
[0045] The torque command generated by the speed control unit 60 is
converted to a voltage command based on a correction made by the
torque control unit 61. The voltage command generated by the torque
control unit 61 is output to the PWM control unit 62 and converted
to a gate control signal. The gate control signal generated by the
PWM control unit 62 is output to the IGBT 23. It is noted that, in
this embodiment, torque of the electric motor 16 is controlled by
feedback control that causes the actual current of the current
sensor 30 to follow a current command corresponding to the torque
command.
[0046] The speed calculating unit 64 calculates the actual speed V
of the upper swing structure id. The speed calculating unit 64
receives an input of rotational position information (resolver
signal) of the electric motor 16 output from the position sensor 24
and, based on the rotational position information, calculates the
actual speed V.
[0047] The fault determining unit 65 determines whether a fault
occurs in the electronic control system (performs a fault
determining process) using the speed command V* received from the
first controller 11 via the communication driver 33a and the actual
speed V calculated by the speed calculating unit 64. The fault
determining process performed by the fault determining unit 65 will
be described in detail using a relevant figure.
[0048] FIG. 6 is a block diagram showing the fault determining unit
65 according to the embodiment of the present invention. As shown
in FIG. 6, the fault determining unit 65 includes an acceleration
calculating unit 82, a backward rotation detecting unit 80, and an
overspeed detecting unit 81.
[0049] The acceleration calculating unit 82 receives an input of
the actual speed V calculated by the speed calculating unit 64. The
acceleration calculating unit 82 calculates the acceleration dV/dt
using the actual speed V input thereto and outputs the calculated
acceleration dV/dt to the backward rotation detecting unit 80 and
the overspeed detecting unit 81. it is noted that the embodiment is
configured so that the acceleration dV/dt is calculated from the
actual speed V when the acceleration of the electric motor 16 is
calculated. The acceleration dV/dt may nonetheless be calculated
from the torque command (target torque) output from the electric
motor 16 or the actual torque generated by the electric motor 16
(that is calculated from the output of the current sensor 30).
Alternatively, instead of the foregoing, an acceleration detector,
such as acceleration sensors and gyro sensors, may be installed and
the output from the acceleration detector is used.
[0050] The backward rotation detecting unit 80 receives inputs of a
speed command (target speed V*) output from the first controller
11, the actual speed V calculated by the speed calculating unit 64,
and the acceleration dV/dt calculated by the acceleration
calculating unit 82. The backward rotation detecting unit 80
determines whether a condition (a first condition) is satisfied or
not, which is satisfied when a sign of a value computed by
subtracting the actual speed V from the target speed V* (value of a
difference in speed) is different from a sign of the acceleration
dV/dt. Based on this determination, the backward rotation detecting
unit 80 determines whether the electric motor 16 rotates backward
as against an instruction of the operator. The example shown in the
figure represents a case in which the sign of the value of the
target speed V* from which the actual speed V is subtracted is
detected to be "positive" and the sign of the acceleration dV/dt is
detected to be "negative."
[0051] The overspeed detecting unit 81 receives inputs of a speed
command (target speed V*) output from the first controller 11, the
actual speed V calculated by the speed calculating unit 64, and the
acceleration dV/dt calculated by the acceleration calculating unit
82. The overspeed detecting unit 81 determines whether a condition
(a second condition) is satisfied or not, which is satisfied when a
difference value between the target speed V* and the actual speed V
is greater than a reference value Vth reference value) and when the
acceleration is greater than a reference value .beta.th (a second
reference value). Based on this determination, the overspeed
detecting unit 81 determines whether the rotational speed of the
electric motor 16 is excessively high as against an instruction of
the operator. Considering the magnitude of the acceleration in
addition to the magnitude of the speed difference enables the
following determination to be made: specifically, when the
acceleration is smaller than the second reference value .beta.th
even with the speed difference being so considerable as to exceed
the first reference value Vth, the considerable speed difference is
attributable to inertia of the upper swing structure ld and the
condition can be determined to be normal. Thus, the inertia of the
upper swing structure ld can be taken into consideration, so that
the likelihood of occurrence of erroneous determination and failure
of detection can be reduced as compared with a case in which focus
is placed only on the speed difference.
[0052] If at least one of the first condition and the second
condition is satisfied in the backward rotation detecting unit 80
or the overspeed detecting unit 81, the fault determining unit 65
determines that a fault (e.g., a faulty IGBT 23 or electric motor
16, or a fault in parts other than the swing control system) has
occurred in the electronic control system relating to the electric
motor 16. The fault determining unit 65 according to the
embodiment, upon determining that a fault has occurred as described
above, outputs a gate off signal to the IGBT 23 to set the electric
motor 16 in a free run state before outputting a braking signal to
the swing emergency brake 25 to brake the electric motor 16.
Operating the swing emergency brake 25 as described above allows
the electric motor 16 to be braked even when the braking cannot be
applied through a control approach by outputting a zero speed
command to the inverter device 13 (specifically, causing the
inverter device 13 to apply a voltage that results in the electric
motor 16 generating deceleration torque).
[0053] An arrangement may even be made in which an annunciating
device that annunciates occurrence of a fault in the hydraulic
excavator based on an annunciation signal is connected to the fault
determining unit 65; when at least one of the first condition and
the second condition is satisfied, as in the above-described case,
an annunciation signal instead of, or together with, the braking
signal is output to the annunciating device, so that the operator
or a supervisor may be advised that a fault has occurred.
Nonlimiting examples of the annunciating device include a display
device 26 (see FIG. 2) disposed near a operator's seat in the cabin
in the hydraulic excavator, a warning light, and an alarm. In this
case, the display device 26 may display a message prompting
inspection or repair of devices, in addition to the message
indicating that a fault has occurred.
[0054] The fault determining process performed in the hydraulic
excavator having the arrangements as described above will be
exemplarily described below. FIGS. 7A, 7B, 7C, and 7D are graphs
showing exemplary relations between the speed command V* and the
actual speed V. Of these, FIGS. 7A and 7B show operations from stop
to swing. In FIG. 7A, the electric motor 16 is accelerated
normally; and neither the first condition nor the second condition
is satisfied, so that the fault determining unit 65 does not
determine a fault. FIG. 7B shows a case in which the electric motor
16 rotates backward against the intention of the operator. In this
case, the sign of the value of the target speed V* from which the
actual speed V is subtracted is "positive" and the sign of the
acceleration dV/dt is "negative." Thus, at least the first
condition is satisfied and a fault can be determined to have
occurred, so that the fault determining unit 65 outputs a braking
signal to the swing emergency brake 25.
[0055] FIGS. 7C and 7D show operations from swing to stop. In FIG.
7C, the operator places the operating lever of the operating device
4b back in the neutral position to make the speed command zero,
thereby bringing the upper swing structure 1d to a stop. In this
case, the electric motor 16 is decelerated normally; and neither
the first condition nor the second condition is satisfied, so that
the fault determining unit 65 does not determine a fault. FIG. 7D
shows an operation in which the operator operates the lever in a
backward rotation direction to thereby bring the upper swing
structure 1d to a stop. In this case, the speed command and the
actual speed are reverse in polarity and a condition in which the
speed difference is excessively great continues to exist; however,
the operation is still normal. In this case, the sign of the value
of the target speed V* from which the actual speed V is subtracted
is "negative" and the sign of the acceleration dV/dt is also
"negative." Thus, the first condition is not satisfied. While the
difference between the target speed V* and the actual speed V is
greater than the first reference value Vth, the acceleration dV/dt
is smaller than the second reference value .beta.th as in the case
of FIG. 7C depicting a normal condition, so that the second
condition is not satisfied, either. Thus, the embodiment can
determine such a case to be normal without making any false
determination.
[0056] In the hydraulic excavator having the arrangements as
described above, erroneous determination relating to the
determination of faults in the electronic control system can be
prevented, which improves availability of the hydraulic excavator
and work efficiency. Additionally, failure of detection relating to
the determination of faults can also be prevented, which improves
reliability.
[0057] In the above-described embodiment, the fault determining
process is performed by using the speed (the speed command V* and
the actual speed V) of the electric motor 16. A process similar to
that mentioned above can also be performed by using torque of the
electric motor 16 (the torque command output from the speed control
unit 60 and the actual torque calculated from the output of the
current sensor 30). Determination accuracy tends to be reduced with
a considerable difference between the speed command V* and the
actual speed V. The performance of the fault determining process
based on the torque as described above can, however, prevent the
determination accuracy from being reduced.
[0058] The above embodiment has been described for a case in which
the fault determining process is performed in the main
microprocessor 31. The speed calculating unit 64 and the fault
determining unit 65 may nonetheless be mounted on the monitoring
microprocessor 32 to enable the monitoring microprocessor 32 to
perform the similar fault determining process function. Similarly
to the main microprocessor 31, the monitoring microprocessor 32
receives the speed command V* from the communication line L2 and
inputs of signals from the position sensor 24 and the current
sensor 30. Thus, the fault determining process described with
reference to FIG. 6 may be performed using the pieces of
information mentioned above and the speed calculating unit 64 and
the fault determining unit 65. When a fault is detected, the
monitoring microprocessor 32 outputs a gate off signal to the IGBT
32 and a braking signal to the swing emergency brake 25. This
enables the monitoring microprocessor 32 to stop the swing motion
of the upper swing structure 1d, even if, for example, a fault
occurs in the main microprocessor 31 and illegal motor control is
performed. It is noted that the monitoring microprocessor 32 does
not need to perform the motor control and is thus not required to
offer calculation performance as high as that of the main
microprocessor 31, so that an inexpensive microprocessor may be
used for the monitoring microprocessor 32. Understandably, the
monitoring microprocessor 32 may be omitted, if the motor control
and the fault determining process are performed only by the main
microprocessor 31 as in the above-described embodiment.
[0059] Another possible arrangement for monitoring the status of
the main microprocessor 31 is, in addition to causing the
monitoring microprocessor 32 to perform the above process with the
monitoring microprocessor 32 and the main microprocessor 31
connected to each other so as to permit communications
therebetween, to combine with the foregoing an example calculation
system in which the monitoring microprocessor 32 sets an
appropriate problem to the main microprocessor 31 and, based on the
answer to the problem from the main microprocessor 31, diagnoses
the main microprocessor 31. An exemplary method of this kind is to
cause the main microprocessor 31 to perform an arithmetic operation
at appropriate intervals and the monitoring microprocessor 32
determines whether a result of the operation is right or wrong to
thereby diagnose the status of the main microprocessor 31.
[0060] Additionally, the above embodiment has been described for a
case in which the communication driver 33b is mounted so as to
allow the monitoring microprocessor 32 to perform a communication
function and to receive the speed command V* directly from the
first controller 11. The use of the communication driver 33b can,
however, be omitted, if the speed command V* is to be received by
way of the main microprocessor 31, which allows the system to be
configured at lower cost. In a configuration such as that described
above, preferably, the first controller 11 transmits the speed
command V* with a check code or a serial number appended to it in
advance, in order to prevent a situation from occurring in which
the monitoring microprocessor 32 receives a false command value
when the main microprocessor 31 is faulty and is thus unable to
detect the fault in the main microprocessor 31. If the main
microprocessor 31 transmits the data directly without its being
processed to the monitoring microprocessor 32, the monitoring
microprocessor 32 can determine that the command value has not been
falsified due to a fault in the main microprocessor 31.
[0061] Fault detection of the first controller 11 and the second
controller 22 can be achieved by mutual monitoring by the first
controller 11 and the second controller 22, in addition to the
embodiment described above. Specific examples of mutual monitoring
by the first controller 11 and the second controller 22 include the
example calculation system described earlier and checking that an
alive counter (a counter that is incremented at every communication
cycle and reset when a predetermined value is reached) is
updated.
[0062] The arrangements of the hydraulic excavator as those
described above can achieve safety of the electronic control system
relating to the upper swing structure id at low cost without
permitting redundancy in each of the controllers, even when any of
the position sensor 24, the controllers 11, 12, the inverter device
13, and the electric motor 16 is faulty. In addition, the output
from the second hydraulic sensor 21 as one of the redundant
hydraulic sensors is applied to the inverter device 13. This
achieves another effect of the present invention to improve
availability of the hydraulic excavator, because a swing motion can
continue even when the first controller 11 that calculates the
swing command or the communication line L2 between the first
controller 11 and the inverter device 13 is faulty.
[0063] The embodiment described above incorporates a crawler type
hydraulic excavator as an example of the construction machine. The
present invention is nonetheless similarly applicable to any other
type of construction machine that includes an upper swing structure
swingably driven an electric motor (e.g., a wheel type hydraulic
excavator and a crawler type or wheel type crane).
DESCRIPTION OF REFERENCE NUMERALS
[0064] 1A Front implement [0065] 1B Vehicle body [0066] 1a Boom
[0067] 1b Arm [0068] 1c Bucket [0069] 1d Upper swing structure
[0070] 1e Lower track structure [0071] 3a Boom cylinder [0072] 3b
Arm cylinder [0073] 3c Bucket cylinder [0074] 3e Left-side track
motor [0075] 3f Right-side track motor [0076] 4a, 4b Operating
device [0077] 5a to 5f Spool type directional control valve [0078]
6 Hydraulic pump [0079] 7 Engine [0080] 8 Relief valve [0081] 9
Hydraulic fluid tank [0082] 10 Driving power conversion machine
[0083] 11 First controller [0084] 12, 13 Inverter device [0085] 14
Chopper [0086] 15 Electric energy storage device [0087] 16 Electric
motor (swing motor) [0088] 20 First hydraulic sensor [0089] 20a
First hydraulic sensor (left side) [0090] 20b First hydraulic
sensor (right side) [0091] 21 Second hydraulic sensor [0092] 21a
Second hydraulic sensor (left side) [0093] 21b Second hydraulic
sensor (right side) [0094] 22 Second controller [0095] 23 IGBT
(inverter circuit) [0096] 24 Position sensor [0097] 25 Swing
emergency brake [0098] 26 Display device [0099] 30 Current sensor
[0100] 31 Main microprocessor [0101] 32 Monitoring microprocessor
[0102] 33a, 33b Communication driver [0103] 60 Speed control unit
[0104] 61 Torque control unit [0105] 64 Speed calculating unit
[0106] 65 Fault determining unit [0107] 80 Backward rotation
detecting unit [0108] 81 Overspeed detecting unit [0109] 82
Acceleration calculating unit [0110] L1 DC electric power line
[0111] L2 Communication line
* * * * *