US20140184122A1 - Construction machine - Google Patents

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 βth. This prevents erroneous determination and failure of detection relating to determination of faults in an electronic control system from occurring.

Description

TECHNICAL FIELD
• The present invention relates to a construction machine including an electric motor for driving a swing structure.
BACKGROUND ART
• 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.
• 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.
• 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 DOCUMENTPatent Document
• Patent Document 1: JP-2007-228721-A
SUMMARY OF THE INVENTIONProblem to be Solved by the Invention
• 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.
• 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
• 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
• 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
• 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.
• FIG. 2 is a configuration diagram showing the construction machine control system according to the embodiment of the present invention.
• 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.
• FIG. 4 is a schematic diagram showing a hardware configuration of aninverter device13 and its surrounding components according to the embodiment of the present invention.
• FIG. 5 is a functional block diagram showing amain microprocessor31 according to the embodiment of the present invention.
• FIG. 6 is a block diagram showing afault determining unit65 according to the embodiment of the present invention.
• FIG. 7A is a graph showing an exemplary relation between a speed command V* and an actual speed V.
• FIG. 7B is a graph showing an exemplary relation between the speed command V* and the speed V.
• FIG. 7C is a graph showing an exemplary relation between the speed command V* and the actual speed V.
• 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
• 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 bycontroller1,controller2,hydraulic sensor1, andhydraulic sensor2, respectively, in the drawings.
• 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 articulatedwork implement1A and avehicle body1B. Thework implement1A includes aboom1a, anarm1b, and abucket1c. Thevehicle body1B includes anupper swing structure1dand alower track structure1e.
• Theboom1ais rotatably supported by theupper swing structure1dand driven by a hydraulic cylinder (boom cylinder)3a.Thearm1bis rotatably supported by theboom1aand driven by a hydraulic cylinder (arm cylinder)3b. Thebucket1cis rotatably supported by thearm1band driven by a hydraulic cylinder (bucket cylinder)3c.Theupper swing structure1dis swingably driven by an electric motor (swing motor)16 (seeFIG. 3). Thelower track structure1eis driven by left and right track motors (hydraulic motors)3eand3f(seeFIG. 3). Thehydraulic cylinder3a,thehydraulic cylinder3b,thehydraulic cylinder3c,and theelectric motor16 are controlled for driving byoperating devices4aand4b(seeFIG. 3) disposed in a cab of theupper swing structure1d, theoperating devices4a,4boutputting hydraulic operating signals.
• 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 theelectric motor16, a position sensor (e.g., magnetic pole position sensor)24, the operating device (swing operating lever)4b,a firsthydraulic sensor20, a secondhydraulic sensor21, afirst controller11, an inverter device (electric power conversion device)13, and aswing emergency brake25. Specifically, theelectric motor16 drives the upper swing structure ld. Theposition sensor24 detects a rotational position of theelectric motor16. Theoperating device4boutputs a hydraulic operating signal (pilot pressure) for a swing motion of the upper swing structure ld according to an amount through which theoperating device4bis operated (operating amount) and a direction in which theoperating device4bis operated (operating direction). The firsthydraulic sensor20 and the secondhydraulic sensor21 each detect pressure corresponding to the hydraulic operating signal output from theoperating device4band output an electric operating signal corresponding to the pressure. Thefirst controller11 calculates a target speed V* of theelectric motor16 based on the electric operating signal output from the firsthydraulic sensor20 and an actual speed V (that may be calculated, for example, from the rotational position detected by the position sensor24) of theelectric motor16 and outputs a control signal (speed command) according to the target speed V*. Theinverter device13 controls theelectric motor16 based on the control signal (speed command) output from thefirst controller11. Theswing emergency brake25 brakes the upper swing structure ld based on a braking signal output from thefirst controller11 or theinverter device13.
• The inverter device (electric power conversion device)13 is connected to an electric energy storage device (seeFIG. 3), such as a battery. Converting direct current (DC) power charged in the electricenergy storage device15 into alternating current (AC) power (three-phase AC) through switching, theinverter device13 supplies the AC power to theelectric motor16 to thereby control theelectric motor16. Theinverter device13 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. Thesecond controller22 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 theinverter device13 are denoted by “IGBT” as an exemplary switching device. Thus, in the following,IGBT23 represents both the inverter circuit and the driver circuit.
• The firsthydraulic sensor20 and the secondhydraulic sensor21 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 operatingdevice4bis detected by the firsthydraulic sensors20 and21 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 theoperating device4bis directly output. In this case, a position sensor that detects rotational displacement of the operating lever in theoperating device4b(e.g., a rotary encoder) may be used. Additionally, in the embodiment, the operatingdevice4bhas twohydraulic sensors20 and21. 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.
• The electric operating signal output from the firsthydraulic sensor20 is applied to thefirst controller11. The electric operating signal output from the secondhydraulic sensor21 is applied to thesecond controller22 disposed in theinverter device13.
• Thefirst controller11 calculates the target speed V* of theelectric motor16 based on the electric operating signal output from the firsthydraulic sensor20 and the actual rotational speed (actual speed V) of theelectric motor16 applied via thesecond controller22. Thefirst controller11 then outputs a control signal (speed command) corresponding to the target speed V* to thesecond controller22.
• Thesecond controller22 outputs a torque command (control signal) generated in consideration of the speed command (control signal) applied thereto from thefirst controller11, 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 theelectric motor16 detected by theposition sensor24, and a current value (actual current) detected by a three-phase motorcurrent sensor30. Thesecond controller22 then turns on or off theIGBT23 based on the torque command, thereby controlling the electric motor16 (seeFIG. 5). Additionally, thesecond controller22 calculates the actual speed V of theelectric motor16 using the rotational position of theelectric motor16 detected by theposition sensor24 and outputs the calculated actual speed V (produces a feedback output) to thefirst controller11.
• It is noted that, in the embodiment, the speed command is output as a command value from thefirst controller11; however, a swing torque command may be used instead. In this case, thesecond controller22 is produce a feedback output of the actual torque value of theelectric motor16 to thefirst controller11.
• 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.
• 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. InFIG. 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).
• InFIG. 3, the operatingdevices4aand4beach 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 theoperating devices4aand4b.The pilot pressure defined according to the operating amount of theoperating device4ais sent to a pressure receiving part of each of spool typedirectional control valves5ato5f.This causes thedirectional control valves5ato5fto change their positions from the neutral positions shown in the figure. Thedirectional control valves5ato5fchange the direction of flow of hydraulic fluid generated from ahydraulic pump6 powered by anengine7 to thereby control driving ofhydraulic actuators3ato3f.Should pressure inside a hydraulic line rise inordinately, the hydraulic fluid is released to atank9 via arelief valve8. Thehydraulic actuators3ato3cserve as the hydraulic cylinders that drive theboom1a, thearm1b, and thebucket1c, respectively. Thehydraulic actuators3eand3fserve as hydraulic motors that drive the left and right track devices disposed at thelower track structure1e.
• A driving power conversion machine (generator motor)10 is connected between thehydraulic pump6 and theengine7. The drivingpower conversion machine10 functions as both a generator and a motor. As the generator, the drivingpower conversion machine10 converts driving power of theengine7 to electric energy and outputs the electric energy toinverter devices12 and13. As the motor, the drivingpower conversion machine10 uses electric energy supplied from the electricenergy storage device15 to assist in driving thehydraulic pump6. Theinverter device12 converts electric energy of the electricenergy storage device15 to AC electric power and supplies the AC electric power to the drivingpower conversion machine10 to assist in driving thehydraulic pump6.
• Theinverter device13 supplies electric power output from the drivingpower conversion machine10 or the electricenergy storage device15 to theelectric motor16 and corresponds to theinverter device13 shown inFIG. 2. Thus, theinverter device13 includes thesecond controller22 shown inFIG. 2. With an input of a speed command (control signal) received from thefirst controller11, theinverter device13 controls driving of theelectric motor16. Theinverter device13 also determines whether a fault occurs in an electronic control system (theelectric motor16, theposition sensor24, and the inverter device13) relating to theelectric motor16 based on the target speed V* defined by the speed command output from thefirst controller11, the actual speed V of theelectric motor16 calculated from a detected value of theposition sensor24, and acceleration dV/dt that is a change with time of the actual speed V of theelectric motor16. The second hydraulic sensors21 (21a,21b) are disposed in, out of pilot lines connecting between the operatingdevices4aand4band thedirectional control valves5ato5f,two pilot lines that control swing motions of the upper swing structure id in clockwise and counterclockwise directions.
• Achopper14 controls voltage of a DC electric power line L1. The electricenergy storage device15 supplies electric power to theinverter devices12 and13 via thechopper14 and stores electric energy generated by the drivingpower conversion machine10 and electric energy regenerated from theelectric motor16. A capacitor, a battery, or both may be used for the electricenergy storage device15.
• Thefirst controller11 calculates the target speed V* of theelectric motor16 based on electric operating signals input from the first hydraulic sensors20 (20a,20b) connected, respectively, to, out of the pilot lines connecting between the operatingdevices4aand4band thedirectional control valves5ato5f,two pilot lines that control the swing motions of theupper swing structure1din the clockwise and counterclockwise directions. Thefirst controller11 then outputs a control signal (swing operating command) according to the calculated target speed V* to theinverter device13. Additionally, thefirst controller11 performs driving power regenerative control that recovers electric energy from theelectric motor16 during swing braking. Furthermore, during the driving power regenerative control and when excess electric power is produced under light hydraulic load, thefirst controller11 performs control to store the recovered electric power and excess electric power in the electricenergy storage device15.
• Theinverter devices12,13, thechopper14, and thefirst controller11 transmit and receive signals required for the control via a communication line L2.
• FIG. 4 is a schematic diagram showing a hardware configuration of theinverter device13 and its surrounding components according to the embodiment of the present invention. As shown inFIG. 4, thesecond controller22 includes a main microprocessor (first microprocessor)31 and a monitoring microprocessor (second microprocessor)32 as control units. Themain microprocessor31 and themonitoring microprocessor32 are control units independent of each other.Communication drivers33aand33bare connected to themain microprocessor31 and themonitoring microprocessor32, respectively, each assuming an interface between the correspondingmicroprocessor31 or32 and the communication line L2.
• Themain microprocessor31 receives inputs of a speed command input from thefirst controller11 via thecommunication driver33a,an electric operating signal output from the secondhydraulic sensor21, rotational position information of theelectric motor16 output from theposition sensor24, and actual current information output from thecurrent sensor30. Using the information from theposition sensor24 and thecurrent sensor30, themain microprocessor31 outputs a gate control signal to theIGBT23 so as to satisfy the speed command input from thefirst controller11 by way of the communication line L2.
• Themonitoring microprocessor32 receives inputs of a speed command input from thefirst controller11 via thecommunication driver33b,an electric operating signal output from the secondhydraulic sensor21, rotational position information of theelectric motor16 output from theposition sensor24, and current information output from thecurrent sensor30. Themonitoring microprocessor32 performs a process of determining whether a fault exists in the electronic control system relating to theelectric motor16 based on the target speed V* of theelectric motor16 defined by the speed command, the actual speed V of theelectric motor16 calculated from the rotational position information from theposition sensor24, and the acceleration dV/dt that is a change with time of the actual speed V of theelectric motor16.
• FIG. 5 is a functional block diagram showing themain microprocessor31 according to the embodiment of the present invention. As shown inFIG. 5, themain microprocessor31 includes aspeed control unit60, atorque control unit61, aPWM control unit62, aspeed calculating unit64, and afault determining unit65. Themain microprocessor31 controls the speed of theelectric motor16 through feedback control.
• Thespeed control unit60 generates a torque command intended for thetorque control unit61 so that the actual speed V calculated by thespeed calculating unit64 follows the speed command (target speed V*).
• Thetorque control unit61 generates a voltage command so that actual torque follows the torque command generated by thespeed control unit60. In addition, if theelectric motor16 cannot be made to follow the torque command output from thespeed control unit60 due to, for example, device performance restrictions relating to the hydraulic excavator, thetorque control unit61 limits the torque command (specifically, reduces as necessary the torque command output from the speed control unit60).
• ThePWM control unit62 generates a gate control signal through pulse width modulation (PWM).
• The torque command generated by thespeed control unit60 is converted to a voltage command based on a correction made by thetorque control unit61. The voltage command generated by thetorque control unit61 is output to thePWM control unit62 and converted to a gate control signal. The gate control signal generated by thePWM control unit62 is output to theIGBT23. It is noted that, in this embodiment, torque of theelectric motor16 is controlled by feedback control that causes the actual current of thecurrent sensor30 to follow a current command corresponding to the torque command.
• Thespeed calculating unit64 calculates the actual speed V of the upper swing structure id. Thespeed calculating unit64 receives an input of rotational position information (resolver signal) of theelectric motor16 output from theposition sensor24 and, based on the rotational position information, calculates the actual speed V.
• Thefault determining unit65 determines whether a fault occurs in the electronic control system (performs a fault determining process) using the speed command V* received from thefirst controller11 via thecommunication driver33aand the actual speed V calculated by thespeed calculating unit64. The fault determining process performed by thefault determining unit65 will be described in detail using a relevant figure.
• FIG. 6 is a block diagram showing thefault determining unit65 according to the embodiment of the present invention. As shown inFIG. 6, thefault determining unit65 includes anacceleration calculating unit82, a backwardrotation detecting unit80, and anoverspeed detecting unit81.
• Theacceleration calculating unit82 receives an input of the actual speed V calculated by thespeed calculating unit64. Theacceleration calculating unit82 calculates the acceleration dV/dt using the actual speed V input thereto and outputs the calculated acceleration dV/dt to the backwardrotation detecting unit80 and theoverspeed detecting unit81. 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 theelectric motor16 is calculated. The acceleration dV/dt may nonetheless be calculated from the torque command (target torque) output from theelectric motor16 or the actual torque generated by the electric motor16 (that is calculated from the output of the current sensor30). 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.
• The backwardrotation detecting unit80 receives inputs of a speed command (target speed V*) output from thefirst controller11, the actual speed V calculated by thespeed calculating unit64, and the acceleration dV/dt calculated by theacceleration calculating unit82. The backwardrotation detecting unit80 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 backwardrotation detecting unit80 determines whether theelectric motor16 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.”
• Theoverspeed detecting unit81 receives inputs of a speed command (target speed V*) output from thefirst controller11, the actual speed V calculated by thespeed calculating unit64, and the acceleration dV/dt calculated by theacceleration calculating unit82. Theoverspeed detecting unit81 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 βth (a second reference value). Based on this determination, theoverspeed detecting unit81 determines whether the rotational speed of theelectric motor16 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 βth 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.
• If at least one of the first condition and the second condition is satisfied in the backwardrotation detecting unit80 or theoverspeed detecting unit81, thefault determining unit65 determines that a fault (e.g., afaulty IGBT23 orelectric motor16, or a fault in parts other than the swing control system) has occurred in the electronic control system relating to theelectric motor16. Thefault determining unit65 according to the embodiment, upon determining that a fault has occurred as described above, outputs a gate off signal to theIGBT23 to set theelectric motor16 in a free run state before outputting a braking signal to theswing emergency brake25 to brake theelectric motor16. Operating theswing emergency brake25 as described above allows theelectric motor16 to be braked even when the braking cannot be applied through a control approach by outputting a zero speed command to the inverter device13 (specifically, causing theinverter device13 to apply a voltage that results in theelectric motor16 generating deceleration torque).
• 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 thefault determining unit65; 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 device26 (seeFIG. 2) disposed near a operator's seat in the cabin in the hydraulic excavator, a warning light, and an alarm. In this case, thedisplay device26 may display a message prompting inspection or repair of devices, in addition to the message indicating that a fault has occurred.
• The fault determining process performed in the hydraulic excavator having the arrangements as described above will be exemplarily described below.FIGS. 7A,7B,7C, and7D 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. InFIG. 7A, theelectric motor16 is accelerated normally; and neither the first condition nor the second condition is satisfied, so that thefault determining unit65 does not determine a fault.FIG. 7B shows a case in which theelectric motor16 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 thefault determining unit65 outputs a braking signal to theswing emergency brake25.
• FIGS. 7C and 7D show operations from swing to stop. InFIG. 7C, the operator places the operating lever of theoperating device4bback in the neutral position to make the speed command zero, thereby bringing theupper swing structure1dto a stop. In this case, theelectric motor16 is decelerated normally; and neither the first condition nor the second condition is satisfied, so that thefault determining unit65 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 theupper swing structure1dto 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 βth as in the case ofFIG. 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.
• 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.
• 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 theelectric motor16. A process similar to that mentioned above can also be performed by using torque of the electric motor16 (the torque command output from thespeed control unit60 and the actual torque calculated from the output of the current sensor30). 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.
• The above embodiment has been described for a case in which the fault determining process is performed in themain microprocessor31. Thespeed calculating unit64 and thefault determining unit65 may nonetheless be mounted on themonitoring microprocessor32 to enable themonitoring microprocessor32 to perform the similar fault determining process function. Similarly to themain microprocessor31, themonitoring microprocessor32 receives the speed command V* from the communication line L2 and inputs of signals from theposition sensor24 and thecurrent sensor30. Thus, the fault determining process described with reference toFIG. 6 may be performed using the pieces of information mentioned above and thespeed calculating unit64 and thefault determining unit65. When a fault is detected, themonitoring microprocessor32 outputs a gate off signal to theIGBT32 and a braking signal to theswing emergency brake25. This enables themonitoring microprocessor32 to stop the swing motion of theupper swing structure1d, even if, for example, a fault occurs in themain microprocessor31 and illegal motor control is performed. It is noted that themonitoring microprocessor32 does not need to perform the motor control and is thus not required to offer calculation performance as high as that of themain microprocessor31, so that an inexpensive microprocessor may be used for themonitoring microprocessor32. Understandably, themonitoring microprocessor32 may be omitted, if the motor control and the fault determining process are performed only by themain microprocessor31 as in the above-described embodiment.
• Another possible arrangement for monitoring the status of themain microprocessor31 is, in addition to causing themonitoring microprocessor32 to perform the above process with themonitoring microprocessor32 and themain microprocessor31 connected to each other so as to permit communications therebetween, to combine with the foregoing an example calculation system in which themonitoring microprocessor32 sets an appropriate problem to themain microprocessor31 and, based on the answer to the problem from themain microprocessor31, diagnoses themain microprocessor31. An exemplary method of this kind is to cause themain microprocessor31 to perform an arithmetic operation at appropriate intervals and themonitoring microprocessor32 determines whether a result of the operation is right or wrong to thereby diagnose the status of themain microprocessor31.
• Additionally, the above embodiment has been described for a case in which thecommunication driver33bis mounted so as to allow themonitoring microprocessor32 to perform a communication function and to receive the speed command V* directly from thefirst controller11. The use of thecommunication driver33bcan, however, be omitted, if the speed command V* is to be received by way of themain microprocessor31, which allows the system to be configured at lower cost. In a configuration such as that described above, preferably, thefirst controller11 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 themonitoring microprocessor32 receives a false command value when themain microprocessor31 is faulty and is thus unable to detect the fault in themain microprocessor31. If themain microprocessor31 transmits the data directly without its being processed to themonitoring microprocessor32, themonitoring microprocessor32 can determine that the command value has not been falsified due to a fault in themain microprocessor31.
• Fault detection of thefirst controller11 and thesecond controller22 can be achieved by mutual monitoring by thefirst controller11 and thesecond controller22, in addition to the embodiment described above. Specific examples of mutual monitoring by thefirst controller11 and thesecond controller22 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.
• 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 theposition sensor24, thecontrollers11,12, theinverter device13, and theelectric motor16 is faulty. In addition, the output from the secondhydraulic sensor21 as one of the redundant hydraulic sensors is applied to theinverter device13. This achieves another effect of the present invention to improve availability of the hydraulic excavator, because a swing motion can continue even when thefirst controller11 that calculates the swing command or the communication line L2 between thefirst controller11 and theinverter device13 is faulty.
• 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
• 1A Front implement
• 1B Vehicle body
• 1aBoom
• 1bArm
• 1cBucket
• 1dUpper swing structure
• 1eLower track structure
• 3aBoom cylinder
• 3bArm cylinder
• 3cBucket cylinder
• 3eLeft-side track motor
• 3fRight-side track motor
• 4a,4bOperating device
• 5ato5fSpool type directional control valve
• 6 Hydraulic pump
• 7 Engine
• 8 Relief valve
• 9 Hydraulic fluid tank
• 10 Driving power conversion machine
• 11 First controller
• 12,13 Inverter device
• 14 Chopper
• 15 Electric energy storage device
• 16 Electric motor (swing motor)
• 20 First hydraulic sensor
• 20aFirst hydraulic sensor (left side)
• 20bFirst hydraulic sensor (right side)
• 21 Second hydraulic sensor
• 21aSecond hydraulic sensor (left side)
• 21bSecond hydraulic sensor (right side)
• 22 Second controller
• 23 IGBT (inverter circuit)
• 24 Position sensor
• 25 Swing emergency brake
• 26 Display device
• 30 Current sensor
• 31 Main microprocessor
• 32 Monitoring microprocessor
• 33a,33bCommunication driver
• 60 Speed control unit
• 61 Torque control unit
• 64 Speed calculating unit
• 65 Fault determining unit
• 80 Backward rotation detecting unit
• 81 Overspeed detecting unit
• 82 Acceleration calculating unit
• L1 DC electric power line
• L2 Communication line

Claims (6)

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 toclaim 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 toclaim 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 toclaim 1, further comprising:

acceleration detecting means that detects acceleration of the electric motor.

5. The construction machine according toclaim 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 toclaim 1, wherein the first control means differs from the second control means.

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