Work machine with lifting magnet

A work machine provided with a lifting magnet includes the lifting magnet, an arm that supports the lifting magnet, a boom that supports the arm, an upper turning body that supports the boom, an engine, a selective catalytic reduction system, and a controller that controls attraction and release by the lifting magnet.

BACKGROUND

Technical Field

The present invention relates to a work machine with a lifting magnet, which is for performing work using the lifting magnet.

Description of Related Art

As a work machine for transporting an object, such as a steel material, a work machine with a lifting magnet has been known. However, related art does not refer to suppression of a nitrogen oxide (NOx) content in an exhaust gas. Thus, the work machine with the lifting magnet according to related art may not sufficiently comply with an exhaust gas regulation.

There is a need for a work machine with a lifting magnet that is capable of suppressing the NOx (nitrogen oxide) content in the exhaust gas.

SUMMARY

According to an aspect of the present disclosure, there is provided a work machine provided with a lifting magnet. The work machine includes the lifting magnet, an arm that supports the lifting magnet, a boom that supports the arm, an upper turning body that supports the boom, an engine, a selective catalytic reduction system, and a controller that controls attraction and release by the lifting magnet.

DETAILED DESCRIPTION

FIG. 1is a side view of a work machine according to an embodiment of the present invention. On a lower traveling body1of the work machine, an upper turning body3is mounted through a turning mechanism2. A boom4is attached to the upper turning body3. An arm5is attached to a tip of the boom4; and a lifting magnet6is attached to a tip of the arm5. Namely, the lifting magnet6is supported by the arm5; the arm5is supported by the boom4; and the boom4is supported by the upper turning body3. The boom4, the arm5, and the lifting magnet6are respectively hydraulically driven by a boom cylinder7, an arm cylinder8, and a lifting magnet cylinder9. In the upper turning body3, a cabin10is formed and a power source, such as an engine11that is an internal combustion engine, is installed.

FIG. 2is a block diagram illustrating a configuration example of a drive system of the work machine shown inFIG. 1. InFIG. 2, a mechanical power system is indicated by a double line, a high-pressure hydraulic line is indicated by a thick solid line, a pilot line is indicated by a broken line, an electric control system is indicated by a one-dot chain line, and an electric drive system is indicated by a thick dotted line.

The drive system ofFIG. 2is mainly formed of an engine11; an alternator11a; a main pump14; a hydraulic pump14G for the lifting magnet; a pilot pump15; a control valve17; an operating device26; a controller30; and an engine control unit74.

The engine11is a driving source of the work machine, and is, for example, a diesel engine that operates to maintain a predetermined revolution number. An output shaft of the engine11is connected to an input shaft of the alternator11a, an input shaft of the main pump14, an input shaft of the hydraulic pump14G for the lifting magnet, and an input shaft of the pilot pump15.

The main pump14is a hydraulic pump that supplies hydraulic oil to the control valve17through a high pressure hydraulic line16, and is, for example, a swash plate type variable displacement hydraulic pump.

A regulator14ais a device for controlling a discharge amount of the main pump14. In this embodiment, the regulator14acontrols the discharge amount of the main pump14by adjusting a swash plate tilt angle of the main pump14, depending on discharge pressure of the main pump14, a control signal from the controller30, etc.

The pilot pump15is a hydraulic pump for supplying, through a pilot line25, hydraulic oil to various types of hydraulic control devices including the operating device26, and is, for example, a fixed displacement type hydraulic pump.

The control valve17is a hydraulic control device for controlling the hydraulic system in the work machine. The control valve17selectively supplies the hydraulic oil discharged by the main pump14to one or more of the boom cylinder7, the arm cylinder8, the lifting magnet cylinder9, a traveling hydraulic motor1A (for right), a traveling hydraulic motor1B (for left), and a turning hydraulic motor2A, for example. In the following description, the boom cylinder7, the arm cylinder8, the lifting magnet cylinder9, the traveling hydraulic motor1A (for right), the traveling hydraulic motor1B (for left), and the turning hydraulic motor2A are collectively referred to as a “hydraulic actuator.”

The operating device26is a device used by an operator to operate the hydraulic actuator. In the embodiment, the operating device26supplies the hydraulic oil from the pilot pump15to a pilot port of a corresponding flow amount control valve in the control valve17to generate pilot pressure. Specifically, the operating device26includes a turning operation lever; a boom operation lever, an arm operation lever, a lifting magnet operation lever, a traveling pedal, etc. The pilot pressure corresponds to operation details of the operating device26(which includes, for example, an operation direction and an operation amount).

A pressure sensor29detects the pilot pressure generated by the operating device26. In the embodiment, the pressure sensor29detects the pilot pressure generated by the operating device26, and outputs the detected value to the controller30. The controller30finds operation details of the operating device26based on the output of the pressure sensor29.

The controller30is a control device for controlling the work machine, and is formed of, for example, a computer including a CPU, a RAM, a ROM, etc. The controller30reads out, from the ROM, programs corresponding to operations or functions of the work machine to load them onto the RAM, and causes the CPU to execute processes corresponding to the programs.

The hydraulic pump14G for the lifting magnet is a pump that supplies hydraulic oil to a hydraulic motor60for the lifting magnet through a high pressure hydraulic line16a. In the embodiment, the hydraulic pump14G for the lifting magnet is a fixed displacement type hydraulic pump, and supplies the hydraulic oil to the hydraulic motor60for the lifting magnet through a switching valve61.

The switching valve61is a valve for switching a flow of hydraulic oil discharged by the hydraulic pump14G for the lifting magnet. In the embodiment, the switching valve61is an electromagnetic valve that switches in response to a control command from the controller30, and is provided with a first position at which the hydraulic pump14G for the lifting magnet and the hydraulic motor60for the lifting magnet are communicated and a second position at which the hydraulic pump14G for the lifting magnet and the hydraulic motor60for the lifting magnet are disconnected.

In response to detecting that a mode changing switch62is operated to switch an operation mode of the work machine to a lifting magnet mode, the controller30outputs a control signal to the switching valve61, so that the switching valve61is switched to the first position. Upon detecting that the mode changing switch62is operated and the operation mode of the work machine is switched to a mode other than the lifting magnetic mode, the controller30outputs a control signal to the switching valve61, so that the switching valve61is switched to the second position.FIG. 2shows a state in which the switching valve61is at the second position. The mode changing switch62is a switch for changing the operation mode of the work machine. In the embodiment, it is a rocker switch installed in the cabin10. An operator operates the mode changing switch62to alternatively switch between a shovel mode and the lifting magnet mode. The shovel mode is a mode for operating the work machine as a shovel, and is selected, for example, when a bucket is attached, instead of the lifting magnet6. The lifting magnet mode is a mode for operating the work machine as the work machine with the lifting magnet, and is selected when the lifting magnet6is attached to the tip of the arm5. The controller30may automatically switch the operation mode of the work machine based on outputs of various sensors.

During the lifting magnet mode, the switching valve61is set to the first position so as to cause the hydraulic oil discharged by the hydraulic pump14G for the lifting magnet to flow into the hydraulic motor60for the lifting magnet. However, during a mode other than the lifting magnet mode, the switching valve61is set to the second position so as to cause the hydraulic oil discharged by the hydraulic pump14G for the lifting magnet to flow out toward a hydraulic tank without causing the hydraulic oil to flow into the hydraulic motor60for the lifting magnet.

A rotational shaft of the hydraulic motor60for the lifting magnet is mechanically connected to a rotational shaft of an electric generator63for the lifting magnet. The electric generator63for the lifting magnet is a generator for generating electric power to magnetize the lifting magnet6. In the embodiment, the electric generator63for the lifting magnet is an AC generator that operates in response to a control command from a power control device64.

The power control device64is a device to control supplying and blocking of power for magnetizing the lifting magnet6. In the embodiment, the power control device64controls start and stop of alternating-current power generation by the electric generator63for the lifting magnet in accordance with a power generation start command or a power generation stop command from the controller30. The power control device64converts alternating-current power generated by the electric generator63for the lifting magnet into direct-current power, and supplies the direct-current power to the lifting magnet6. The power control device64can control an absolute value of a direct-current voltage to be applied to the lifting magnet6.

Upon detecting that a lifting magnet switch65is turned, so that it is in an ON state, the controller30outputs an attraction command to the power control device64. Upon receiving the attraction command, the power control device64converts alternating-current power generated by the electric current generator63for the lifting magnet into direct-current power, and supplies the direct-current power to the lifting magnet6, so that the lifting magnet6is magnetized. The magnetized lifting magnet6is in an attraction state in which the lifting magnet6can attract an object. At this time, the controller30sets an attraction flag with an initial value of “0” to “1.” The attraction flag is a flag representing an attraction state of the lifting magnet6. The value “0” represents a non-attraction state (release state), and the value “1” represents the attraction state. Release of the lifting magnet6means an operation in which supply of power to the lifting magnet6is stopped, so that electromagnetic force generated by the lifting magnet is eliminated.

Upon detecting that the lifting magnet switch65is turned-off, so that it is in an OFF state, the controller30outputs a release command to the power control device64. Upon receiving the release command, the power control device64causes the power generation by the electric generator63for the lifting magnet to be stopped, so that the lifting magnet6in the attraction state is in the non-attraction state (the release state). At this time, the controller30sets the value of the attraction flag to “0.”

The lifting magnet switch65is for switching between attraction and release of the lifting magnet6. In the embodiment, the lifting magnet switch65is a push button switch provided at a top of at least one of left and right operation levers for operating the turning mechanism2, the boom4, the arm6, and the lifting magnet6. The lifting magnet switch65may be configured such that, each time the button is pushed, the ON state and the OFF state are alternately switched, or may be configured such that a button for the ON operation and a button for the OFF operation are separately prepared.

With this configuration, the work machine can perform work, such as attracting and conveying an object, by the lifting magnet6, while operating the hydraulic actuator by hydraulic oil discharged by the main pump14.

A fuel residual amount sensor50ais an example of a fuel storage amount detector, and is for detecting a residual amount of fuel in a fuel tank as a fuel storage unit. In the embodiment, the fuel residual amount sensor50aoutputs information about the detected residual amount of the fuel to the controller30. Specifically, the fuel residual amount sensor50ais formed of a float that follows a variation of a liquid surface of the fuel inside the fuel tank; and a variable resistance (potentiometer) that converts vertical fluctuation of the float into a resistance value. With this configuration, the fuel residual amount sensor50acan continuously detect a residual state of the fuel. A detection method of the fuel residual amount sensor50amay be appropriately selected depending on a usage environment, and a detection method may be adopted that can stepwise detect the residual state of the fuel.

A urea water residual amount sensor55ais an example of a reducing agent storage unit, and is for detecting a residual amount of urea water in the urea water tank55as a reducing agent storage unit. In the embodiment, the urea water residual amount sensor55aoutputs information about the detected residual amount of the urea water to the engine control unit74. The engine control unit74outputs the information about the residual amount of the urea water received from the urea water residual amount sensor55ato the controller30. Specifically, the urea water residual amount sensor55ais formed of a float in which a magnet is fixed; and a plurality of magnetically driven reed switches installed at respective different heights. The urea water residual amount sensor55adetects a residual amount state of the urea water using that a reed switch corresponding to a position of the float that follows variation of a liquid surface of the urea water inside the urea water tank55becomes a conductive state. More specifically, the urea water residual amount sensor55ais provided with eight reed switches arranged at equal intervals. With this configuration, the urea water residual amount sensor55acan detect the residual amount state of the urea water in eight steps. A detection method of the urea water residual amount sensor55acan be appropriately selected depending on a usage environment, a freezing point of the urea water, etc., and a detection method may be adopted that can continuously detect the residual amount state of the urea water.

An image display device40is a device for displaying various types of information. In the embodiment, the image display device40is fixed to a pillar of the cabin10, in which a driver's seat is formed. As illustrated inFIG. 2, the image display device40can display an operating condition and control information of the work machine on an image display unit41to provide the information to a driver. The image display device40includes a switch panel42as an input unit. A driver can input information and a command to the controller30of the work machine using the switch panel42.

The switch panel42is a panel including various types of hardware switches. In the embodiment, the switch panel42includes a light switch42a; a wiper switch42b; and a window washer switch42c, as hardware buttons. The light switch42ais for switching between turning on and off of a light attached to an outer part of the cabin10. The wiper switch42bis for switching between turning on and off of a wiper. The window washer switch42cis a switch for injecting a window washer liquid.

The image display device40operates by receiving supply of electric power from a storage battery70. The storage battery70is charged with electric power that is generated by the alternator11a. The electric power of the storage battery70is also supplied to an electrical component72of the work machine other than the controller30and the image display device40. A starter11bof the engine11is driven by electric power from the storage battery70to start the engine11.

The engine control unit74is a device for controlling the engine11. In the embodiment, the engine control unit74collects various types of data indicating a state of the engine11, and transmits the collected data to the controller30. In the embodiment, the engine control unit74and the controller30are famed as separate bodies; however, they may be integrally formed. For example, the engine control unit74may be integrated into the controller30.

An engine revolution number adjusting dial75is a dial for adjusting an engine revolution number. In the embodiment, the engine revolution number adjusting dial75is installed inside the cabin10, so that the engine revolution number can be switched in four steps. The engine revolution number adjusting dial75outputs data indicating a setting condition of the engine revolution number to the controller30. The engine revolution number adjusting dial75allows the engine revolution number to be switched in the four steps, which are a SP mode, a H mode, an A mode, and an idling mode.FIG. 2shows a state in which the H mode is selected by the engine revolution number adjusting dial75.

The SP mode is a revolution number mode to be selected when volume of work is to be prioritized, and uses the largest revolution number. The H mode is a revolution number mode to be selected when volume of work and fuel consumption are to be balanced, and uses the second largest revolution number. The A-mode is a revolution number mode to be selected when it is desired to operate the work machine with low noise while prioritizing fuel consumption, and uses the third largest revolution number. The idling mode is a revolution number mode to be selected when the engine is to be in an idling mode, and uses the smallest engine revolution number (idling revolution number). The revolution number of the engine11is controlled to be a constant engine revolution number of the revolution number mode that is selected by the engine revolution number adjusting dial75.

Next, referring toFIG. 3, a selective reducing catalyst system100is described, which is to be installed in the work machine ofFIG. 1. Note thatFIG. 3is a schematic diagram illustrating an example of a configuration of the selective reducing catalyst system100. The selective reducing catalyst system100is an example of an exhaust gas purifying system, and purifies the exhaust gas emitted from the engine11.

Fuel is supplied to the engine11from the fuel tank by a high pressure pump. This high pressure fuel is directly injected into a combustion chamber, and the high pressure fuel burns. The engine11, the high pressure pump, and so forth are controlled by the engine control unit74.

The exhaust gas from the engine11passes through a turbocharger80, and then flows into a downstream exhaust pipe81. After a purifying process by the selective reducing catalyst system100is applied, the exhaust gas is discharged into the atmosphere.

The intake air drawn from an air cleaner82into an air inlet pipe83passes through the turbocharger80and an intercooler84to be supplied to the engine11.

In the exhaust pipe81, a diesel particulate filter85that collects particulates in the exhaust gas and a selective reducing catalyst86for reducing and removing NOx in the exhaust gas are serially arranged.

The selective reducing catalyst86receives supply of a liquid reducing agent (e.g., urea or ammonia) and continuously reduces and removes NOx in the exhaust gas. In the embodiment, from the view point of ease of handling, urea water (aqueous urea solution) is used as the liquid reducing agent.

At an upstream side of the selective reducing catalyst86, a urea water injection device87is provided, which is for supplying the urea water to the selective reducing catalyst86. The urea water injection device87is connected to the urea water tank55through a urea water supply line88.

Furthermore, in the urea water supply line88, a urea water supply pump89is provided, and a filter90is provided between the urea water tank55and the urea water supply pump89. The urea water stored in the urea water tank55is supplied to the urea water injection device87by the urea water supply pump89, and is injected from the urea water injection device87to an upstream position of the selective reducing catalyst86in the exhaust pipe81.

The urea water injected from the urea water injection device87is supplied to the selective reducing catalyst86. The supplied urea water is hydrolyzed in the selective reducing catalyst86to produce ammonia. This ammonia reduces the NOx included in the exhaust gas in the selective reducing catalyst86, and by this reduction reaction of the NOx, the exhaust gas is purified.

A first NOx sensor91is disposed at an upstream side of the urea water injection device87. Furthermore, a second NOx sensor92is disposed at a downstream side of the selective reducing catalyst86. The NOx sensors91and92detect NOx concentration in the exhaust gas at respective disposed positions.

In the urea water tank55, the urea water residual amount sensor55ais disposed. The urea water residual amount sensor55adetects a urea water residual amount in the urea water tank55.

The NOx sensors91and92, the urea water residual amount sensor55a, the urea water injection device87, and the urea water supply pump89are connected to a selective reducing catalyst system controller93. Based on the NOx concentration detected by the NOx sensors91and92, the selective reducing catalyst system controller93controls an injection amount, so that an appropriate amount of urea water is injected into the exhaust pipe81by the urea water injection device87and the urea water supply pump89.

Based on the urea water residual amount output from the urea water residual amount sensor55a, the selective reducing catalyst system controller93calculates a ratio of the urea water residual amount with respect to the total volume of the urea water tank55(which is referred to as a “urea water residual amount ratio,” hereinafter). For example, the urea water residual amount ratio of 50% indicates that the urea water corresponding to a half of the volume of the urea water tank55remains in the urea water tank55.

The selective reducing catalyst system controller93is connected to the engine control unit74by a communication unit. Furthermore, the engine control unit74is connected to the controller30by a communication unit. Note that, in the embodiment, the selective reducing catalyst system controller93, the engine control unit74, and the controller30are formed as separate bodies; however, at least two of them may be integrally famed. For example, the selective reducing catalyst system controller93may be integrated in the engine control unit74.

It is configured such that various types of information about the selective reducing catalyst system100owned by the selective reducing catalyst system controller93can be shared by the controller30and the engine control unit74. Similar to the controller30, each of the engine control unit74and the selective reducing catalyst system controller93includes a CPU, a RAM, a ROM, an input/output port, a storage device, etc. The engine control unit74determines an injection amount of the urea water depending on the collected data. Then, the engine control unit74transmits a control signal to the urea water injection device87through the selective reducing catalyst system controller93to control the injection amount of the urea water to the exhaust gas from the engine11.

Next, referring toFIG. 4, an operation state of the work machine ofFIG. 1is described, which transitions in response to a decrease in the urea water amount. Here,FIG. 4is a state transition diagram of the work machine ofFIG. 1.

As illustrated inFIG. 4, the operation state of the work machine ofFIG. 1transitions in three stages, which are a normal stage, an alerting stage, and a use restriction stage, depending on the decrease in the urea water residual amount.

In the normal stage, the work machine operates without receiving any restriction on the urea water residual amount. Then, upon detecting that the urea water residual amount becomes less than a predetermined amount, the operation state of the work machine transitions from the normal stage to the alerting stage. In the embodiment, upon detecting that the urea water residual amount ratio becomes less than the predetermined value TH1(e.g., 5%), the operation state of the work machine transitions from the normal stage to the alerting stage. It is preferable that the predetermined value TH1be set within a range from 3% to 10%.

At the alerting stage, the work machine operates while receiving a predetermined restriction on the urea water residual amount. In the embodiment, the controller30causes the image display device40to display a text message indicating that the urea water residual amount ratio becomes less than the predetermined threshold value TH1. Furthermore, even if the lifting magnet switch65is turned on in the lifting magnet mode, the controller30does not allow the lifting magnet6to be magnetized. The reason is to prevent the lifting magnet6from being forcibly released when the engine revolution number has to be reduced due to the shortage of the urea water in the subsequent work. However, upon detecting that the lifting magnet6has already been in the attraction state at the time of the transition from the normal stage to the alerting stage, the controller30allows the magnetization of the lifting magnet6to be continued without releasing the lifting magnet6. The reason is to prevent an object attracted by the lifting magnet6from being dropped. In this case, the controller30may cause the image display device40to display a text message prompting release of the lifting magnet6. Note that, even if the magnetization of the lifting magnet6is continued at the time of the transition from the normal stage to the alerting stage, if the lifting magnet6is released after that, the controller30does not allow the lifting magnet6to be magnetized, even if the lifting magnet switch65is turned on in the lifting magnet mode.

Then, upon detecting that the duration of the alerting stage becomes greater than or equal to a predetermined time period, or that the urea water residual amount ratio becomes another predetermined value TH2(e.g., 0%), the operation state of the work machine transitions from the alerting stage to the use restriction stage. Here, it is preferable that the predetermined value TH2be set within a range from 0% to 1%. Furthermore, when the urea water is supplied, the operation state of the work machine transitions from the alerting stage to the normal stage.

At the use restriction stage, the work machine operates while receiving a predetermined additional restriction on the urea water residual amount. In the embodiment, the controller30causes the image display device40to display a text message indicating that the urea water residual amount ratio becomes the predetermined value TH2. Furthermore, the engine control unit74reduces the engine revolution number to be a predetermined revolution number. The predetermined revolution number may be a minimum revolution number at which the attraction force of the lifting magnet6can be maintained, or an idling revolution number. In this case, the controller30may cause the image display device40to display a text message indicating that the engine revolution number has been reduced.

However, upon detecting that the lifting magnet6has already been in the attraction state at the time of the transition from the alerting stage to the use restriction stage, the controller30allows the engine11to continue driving at the current engine revolution number without reducing the engine revolution number. The reason is to prevent the lifting magnet6from being forcibly released, and to prevent an object that has been attracted by the lifting magnet6from being dropped.

Specifically, the engine control unit74causes the engine revolution number to be decreased to a predetermined revolution number; however, even after the engine revolution number is reduced to the predetermined revolution number, the engine revolution number is allowed to be adjusted toward the increasing side, only for a predetermined number of times (e.g., once). In the following, the function of the controller30to increase the engine revolution number after the engine control unit74reduces the engine revolution number to the predetermined revolution number is referred to as the “escape function.” Additionally, an operation mode of the work machine after the controller30has increased the engine revolution number using this escape function is referred to as the “escape mode.” The engine control unit74may limit the time to allow the engine revolution number to be adjusted toward the increasing side. Upon detecting that the urea water residual ratio becomes 0%, the engine control unit74may disallow execution of the escape function.

The controller30uses this escape function to cause the engine revolution number to be increased, immediately after the engine revolution number has been decreased to the predetermined revolution number. For example, the controller30causes the engine revolution number to be automatically returned to the original revolution number, or causes the engine revolution number to be automatically increased to a revolution number at which the attraction force of the lifting magnet6can be maintained. Then, the reduction in the engine revolution number, which has been caused by the engine control unit74for preventing an increase in NOx in the exhaust gas due to the shortage of the urea water, is disabled. In this case, the controller30may cause the image display device40to display a text message prompting an early release of the lifting magnet6. Note that the revolution number at which the attraction force of the lifting magnet6can be maintained is a value that is derived from a specification value of the lifting magnet6, and, in the embodiment, it is stored in advance in the ROM, etc.

Furthermore, even if the reduction in the engine revolution number is disabled at the time of the transition from the alerting stage to the use restriction stage to continue the lifting magnet6to be magnetized, if, after that, the lifting magnet6is released, the controller30, then, causes the engine revolution number to be decreased. Furthermore, even if the lifting magnet switch65is turned on in the lifting magnet mode, the lifting magnet6is not to be magnetized. When the urea water is supplied, the operating state of the work machine transitions from the use restriction stage to the normal stage.

Next, referring toFIG. 5, a process at the time of the transition from the normal stage to the alerting stage (which is referred to as the “alerting stage transition process,” hereinafter) is described. Note thatFIG. 5is a flowchart illustrating a flow of the alerting stage transition process. The controller30repeatedly executes the alerting stage transition process at a predetermined control cycle.

First, the controller30determines whether the urea water residual amount ratio becomes less than the predetermined value TH1(step S1). In the embodiment, the controller30compares the urea water residual amount ratio calculated by the selective reducing catalyst system controller93based on the output of the urea water residual amount sensor55awith the predetermined value TH1(e.g., 5%), which is set in the ROM, etc., in advance.

In response to determining that the urea water residual amount ratio is greater than or equal to the predetermined value TH1(NO at step S1), the controller30terminates the alerting stage transition process for this time, without disallowing the lifting magnet6to be magnetized.

In response to determining that the urea water residual amount ratio is less than the predetermined value TH1(YES at S1), the controller30calls attention of a driver of the work machine (step S2). In the embodiment, the controller30outputs a control command to the image display device40so as to cause the image display unit41to display a text message indicating that the urea water residual amount ratio becomes less than the predetermined value TH1. Then, the driver of the work machine is prompted to supply the urea water. In addition to or instead of causing the image display unit41to display the text message, the controller30may cause a vehicle-mounted speaker, etc., to output a voice message, may cause a remaining amount warning lamp, etc., to be turned on, or may cause a warning buzzer, etc., to make a sound.

After that, the controller30determines whether the operation mode of the work machine is the lifting magnet mode (step S3). In the embodiment, the controller30determines whether the operation mode of the working machine is the lifting magnet mode of the shovel mode, based on the output of the mode changing switch62.

In response to determining that the operation mode of the work machine is not the lifting magnet mode (NO at step S3), the controller30starts a restriction to disallow attraction (step S4).

The restriction to disallow the attraction is a function to disallow the lifting magnet6to be magnetized (attraction of an object by the lifting magnet6). In the embodiment, when the restriction to disallow the attraction is started, the controller30does not allow the lifting magnet6to be magnetized, even if the lifting magnet switch65is turned on. When the restriction to disallow the attraction is started once, the controller30does not release the restriction to disallow the attraction until the urea water is supplied.

Specifically, when the restriction to disallow the attraction is started, the controller30sets a value of an attraction disallow flag, which has an initial value of “0,” to “1.” The attraction disallow flag is a flag representing whether the restriction to disallow the attraction is started, the value “0” represents a non-started state (a state in which the restriction to disallow the attraction is not started), and the value “1” represents a started state (a state in which the restriction to disallow the attraction is started). Then, when a power generation start command is to be output to the power control device64, the controller30refers to the value of the attraction disallow flag. If the value is “0,” the power generation start command is to be output. If the value is “1,” the power generation start command is not to be output.

Furthermore, in response to determining that the operation mode of the work machine is the lifting magnet mode (YES at step S3), the controller30determines whether the lifting magnet6is in the attraction state (step S5).

In response to determining that the lifting magnet6is not in the attraction state (NO at step S5), the controller30starts the restriction to disallow the attraction (step S4). In the embodiment, in response to determining that the lifting magnet6is not in the attraction state, namely, it is in the non-attraction state, based on the output of the lifting magnet switch65(NO at step S5), the controller30starts the restriction to disallow the attraction. Then, even if the lifting magnet switch65is turned on, the lifting magnet6is not to be magnetized. The reason is to prevent the lifting magnet6from being forcibly released when the engine revolution number has to be reduced due to the shortage of the urea water in the subsequent work. In the following, the operation mode of the work machine in this state is referred to as the “lifting magnet release mode.”

In contrast, upon determining that the lifting magnet6is in the attraction state (YES at step S5), the controller30terminates the alerting stage transition process for this time, without starting the restriction to disallow the attraction. The reason is to prevent an attracted object from being dropped. In the following, the operation mode of the work machine in this state is referred to as the “attraction drop prevention mode.”

Furthermore, when the lifting magnet6is released in the attraction drop prevention mode, the controller30determines that the lifting magnet6is not in the attraction state, and starts the restriction to disallow the attraction at that time point so as to cause the operation mode of the work machine to transition to the lifting magnet release mode.

As described above, the controller30causes the control state of the lifting magnet6to be changed depending on the state of the urea water tank55(e.g., the urea water residual amount) used in the selective reducing catalyst system100.

With the above-described configuration, the work machine ofFIG. 1reduces and removes NOx in the exhaust gas using the selective reducing catalyst86. Consequently, the content of NOx (nitrogen oxide) in the exhaust gas can be suppressed.

Even if the restriction to disallow the attraction is to be started due to the shortage of the urea water, if the lifting magnet6is attracting an object, the controller30causes the restriction to disallow the attraction not to be started. Consequently, the controller30can prevent the magnetic force of the lifting magnet6from being reduced or lost, due to lowering of the output of the electric generator63for the lifting magnet by starting of the restriction to disallow the attraction caused by the shortage of the urea water, so that the controller30can prevent an object attracted by the lifting magnet6from being dropped.

Next, referring toFIG. 6, a process at the time of the transition from the alerting stage to the use restriction stage (which is referred to as the “use restriction stage transition process,” hereinafter) is described. Here,FIG. 6is a flowchart illustrating a flow of the use restriction stage transition process. The controller30repeatedly executes the use restriction stage transition process at a predetermined control cycle.

First, the controller30determines whether the duration of the alerting step becomes greater than or equal to a predetermined time interval (step S11). Note that the controller30may determine whether the urea water residual amount ratio becomes the predetermined value TH2, instead of determining whether the duration of the alerting step becomes greater than or equal to the predetermined time interval.

In response to determining that the duration of the alerting step is less than the predetermined time interval (NO at step S11), the controller30terminates the use restriction stage transition process for this time, without causing the engine revolution number to be reduced.

In response to determining that the duration of the alerting step becomes greater than or equal to the predetermined time interval (YES at step S11), the controller30outputs a warning (step S12). In the embodiment, the controller30outputs a control command to the image display device40so as to cause the image display unit41to display a text message indicating that the urea water residual amount is almost running out. Then, the driver of the work machine is prompted to supply the urea water early. In addition to or instead of causing the image display unit41to display the text message, the controller30may cause a vehicle-mounted speaker, etc., to output a voice message.

After that, the controller30determines whether the operation mode of the work machine is the lifting magnet mode (step S13). In the embodiment, the controller30determines whether the operation mode of the work machine is the lifting magnet mode or the shovel mode, based on the output of the mode changing switch62.

In response to determining that the operation mode of the work machine is not the lifting magnet mode (NO at step S13), the controller30accepts reduction of the engine revolution number caused by the engine control unit74(step S14). Specifically, when the duration of the alerting step exceeds the predetermined time interval, the engine control unit74forcibly reduces the engine revolution number irrespective of the control by the controller30. The controller30does not perform any processing on the reduction of the engine revolution number caused by the engine control unit74. Furthermore, when the engine revolution number is reduced once, the engine control unit74disallows the engine revolution number to be increased until the urea water is supplied.

In response to detecting that the operation mode of the work machine is the lifting magnet mode (YES at step S13), the controller30determines whether the lifting magnet6is in the attraction state (step S15).

Then, upon detecting that the lifting magnet6is not in the attraction state (NO at step S15), the controller30accepts the reduction of the engine revolution number caused by the engine control unit74(step S14). In the embodiment, upon determining that the lifting magnet6is not in the attraction state, namely, it is in the non-attraction state, based on the output of the lifting magnet switch65(NO at step S15), the controller30accepts the reduction of the engine revolution number caused by the engine control unit74. In the following, the operation mode of the work machine in this state is referred to as the “use restriction mode.” The reason is that, due to the reduction of the engine revolution number, the absorption horsepower that can be consumed by the main pump14is limited. In the use restriction mode, even if the lifting magnet switch65is turned on, the controller30does not allow the lifting magnet6to be magnetized. The reason is to prevent the lifting magnet6from being forcibly released when the engine revolution number has to be reduced due to the shortage of the urea water in the subsequent work, and to prevent an object attracted by the lifting magnet6from being dropped.

Upon determining that the lifting magnet6is in the attraction state (YES at S15), the controller30disables the reduction of the engine revolution number caused by the engine control unit74(step S16). The reason is to prevent an attracted object from being dropped.

Specifically, the controller30causes the engine revolution number to be returned to the original revolution number immediately after the engine revolution number is reduced to be the predetermined revolution number by the engine control unit74so as to disable the reduction of the engine revolution number caused by the engine control unit74. At this time, the operation mode of the work machine is the “escape mode.”

When the lifting magnet6is released in the escape mode, the controller30determines that the lifting magnet6is not in the attraction state, and causes, at that time point, the operation mode of the work machine to transition from the escape mode to the use restriction mode. As a result, the engine control unit74reduces the engine revolution number to be the predetermined revolution number. The reason is to suppress the emission amount of NOx, and to disallow the operation of the work machine to continue.

As described above, the controller30causes the control state of the lifting magnet6to be changed depending on the state of the urea water tank55(e.g., the duration of the state in which the residual amount of the urea water is less than the predetermined value TH1) used in the selective reducing catalyst system100.

With the above-described configuration, the work machine ofFIG. 1reduces and removes NOx in the exhaust gas using the selective reducing catalyst86. Consequently, the emission amount of NOx (nitrogen oxide) included in the exhaust gas can be reduced.

Furthermore, even if the engine control unit74executes, due to the shortage of the urea water, the output restriction of the engine11(the reduction of the engine revolution number), if the lifting magnet6is attracting an object, the controller30disables the reduction of the engine revolution number. Consequently, the controller30can prevent the magnetic force of the lifting magnet6from being reduced or lost, due to lowering of the output of the electric generator63for the lifting magnet by the reduction of the engine revolution number caused by the shortage of the urea water, so that the controller30can prevent an object attracted by the lifting magnet6from being dropped.

Furthermore, the controller30preferentially disables the reduction of the engine revolution number over monitoring of the urea water residual amount by the selective reducing catalyst system controller93and the output restriction of the engine11by the engine control unit74. Consequently, even if the selective reducing catalyst system controller93and the engine control unit74execute their original functions, it can be prevented that, when the lifting magnet6is attracting an object, the output of the electric generator63for the lifting magnet is lowered and the magnetic force of the lifting magnet6is reduced or lost.

The preferred embodiment of the present invention is described above. However, the present invention is not limited to the above-described embodiment, and various modifications and substitutions may be added to the above-described embodiment without departing from the scope of the present invention.

For example, in the above-described embodiment, upon detecting that the urea water residual amount ratio becomes less than the predetermined value TH1, the controller30determines whether the restriction to disallow the attraction is to be started; or upon detecting that the duration of the alerting stage is greater than or equal to the predetermined time interval, the controller30determines whether the reduction of the engine revolution number is to be disabled. However, the present invention is not limited to this configuration. For example, the controller30may detect quality of the urea water based on outputs of various sensors; and, upon detecting an abnormality in the quality of the urea water, the controller30may determine whether the restriction to disallow the attraction is to be started. Similarly, upon detecting an abnormality in the quality of the urea water, the controller30may determine whether the reduction of the engine revolution number is to be disabled.