Patent Publication Number: US-7222051-B2

Title: Working machine, failure diagnosis system for work machine and maintenance system for work machines

Description:
This is a Division of application Ser. No. 10/476,606 filed May 13, 2004 now U.S. Pat. No. 7,079,982, which is a National Stage of PCT/JP02/04262 filed Apr. 26, 2002. The entire disclosure of the prior applications is hereby incorporated by reference herein in its entirety. 

   INCORPORATION BY REFERENCE 
   The disclosures of the following priority applications are herein incorporated by reference:
     Japanese Patent Application No. 2001-137809 filed May 8, 2001   Japanese Patent Application No. 2001-219601 filed Jul. 19, 2001.   

   TECHNICAL FIELD 
   The present invention relates to a failure diagnosis and maintenance performed on a working machine and, more specifically, it relates to a failure diagnosis and maintenance performed on a construction working machine such as a hydraulic excavator. 
   BACKGROUND ART 
   There are systems in the related art in which information (operation data) from construction working machines is transmitted to an information management center where operation data are used to forecast whether or not there is a failure (e.g., Japanese Laid-Open Patent Publication No. 2000-259729). The forecast information generated at the center is provided to the maintenance personnel and a maintenance person performs maintenance work or the like based upon the information thus provided. 
   However, in the system disclosed in the publication quoted above, the information from the center is not directly provided to the operator operating the working machine and, as a result, it takes a considerable length of time for the operator to ascertain the exact location of the failure and the cause of the failure in the working machine. This gives rise to a concern that when a failure occurs, the operator may not be able to take appropriate action in a timely manner. 
   In addition, failure repair data or maintenance completion data transmitted by the service personnel upon completing a repair on a failed machine or completing maintenance work are provided to a database at the center server through a manual input by the service personnel or a clerk in the office to which the service personnel report. Under certain circumstances, the data can be inadvertently left unentered or input erroneously. This, in turn, leads to a problem in that an unpredicted failure can occur through a failure to perform appropriate maintenance on the individual working machines. 
   DISCLOSURE OF THE INVENTION 
   The present invention provides a working machine, a failure diagnosis system for working machines and a maintenance system for working machines that provide an operator with appropriate information indicating a failure location in a working machine and the like and enable maintenance work to be performed on the working machine. 
   A working machine failure diagnosis method for performing a failure diagnosis by transmitting and receiving signals through communication devices provided at a working machine and at an information management center, according to the present invention, comprises: a first step in which a first signal related to a failure of the working machine is generated at the working machine and the first signal is transmitted to the information management center from the working machine via the communication devices; a second step in which, after the first signal is transmitted, the information management center generates a second signal for identifying a location of the failure based upon the first signal and the second signal is then transmitted from the information management center to the working machine via the communication devices; and a third step in which failure information corresponding to the first signal and the second signal is provided to an operator. 
   In this working machine failure diagnosis method, it is preferred that the first step starts upon a detection of an abnormal state at the working machine. 
   Also, it is preferred that the first step starts as an abnormality occurrence signal is input at the working machine when an abnormality has occurred at the working machine. 
   Also, it is preferred that there are further provided a fourth step in which a signal related to a service request for the identified failure location is transmitted from the working machine to the information management center, and a fifth step in which a servicing cost and a length of servicing time are calculated at the information management center based upon the signal related to the service request and information indicating the cost and the length of time is transmitted to the working machine. 
   Also, it is preferred that there are further provided a fourth step in which a signal related to a service request for the identified failure location is transmitted from the working machine to the information management center, and a fifth step in which a time point at which a service person is expected to arrive at a site is calculated at the information management center based upon the signal related to the service request and information indicating the time point is transmitted to the working machine. 
   A working machine failure diagnosis system according to the present invention comprises: a first signal generating device that generates at a working machine a first signal related to a failure of the working machine; a first transmission device that transmits the first signal from the working machine to an information management center; a second signal generating device that generates at the information management center a second signal for identifying a location of the failure based upon the first signal after the first signal is transmitted thereto; a second transmission device that transmits the second signal from the information management center to the working machine; and an informing device that provides an operator with failure information corresponding to the first signal and the second signal. 
   In this working machine failure diagnosis system, it is preferred that: the working machine includes a detection device that detects an abnormal state therein; and when an abnormal state is detected by the detection device, the first signal generating device generates the first signal based upon detection results. 
   Also, it is preferred that: the working machine includes an operating unit that is operated when an abnormality occurs therein; and when an abnormality occurrence signal is input through the operating unit, the first signal generating device generates the first signal based upon the abnormality concurrence signal. 
   Also, it is preferred that: the second signal contains information for identifying the failure location; and the informing device informs the operator of the identified failure location. In this case, it is preferred that: the information management center includes a service management device that calculates a servicing cost and a length of servicing time after a signal related to a service request is transmitted from the working machine following identification of the failure location; and the second signal generating device generates the second signal that contains information indicating the servicing cost and length of servicing time. Also, it is preferred that: the information management center includes a schedule management device that calculates a time point at which a service person is expected to arrive at a site after a signal related to a service request is transmitted from the working machine following identification of the failure location; and the second signal generating device generates the second signal that contains information indicating the arrival time point. 
   A working machine according to the present invention comprises: a signal generating device that generates a signal related to failure information; a transmission device that transmits the signal which has been generated to an information management center; a reception device that receives a signal related to a failure diagnosis returned from the information management center in response to the signal transmitted via the transmission device; and an informing device that provides failure information based upon the signal that has been received. 
   In this working machine, it is preferred that: there is further provided an automatic abnormality detection device that automatically detects an abnormal state in the working machine; and the signal generating process generates the signal related to the failure information when the abnormal state is detected by the automatic abnormality detection device. 
   Also, it is preferred that: there are further provided an input device through which a failure diagnosis instruction is received from an operator, and an abnormality detection device that detects whether or not an abnormal state is present in the working machine when the failure diagnosis instruction is received through the input device; and the signal generating process generates the signal related to the failure information when the abnormal state is detected by the abnormality detection device. 
   Also, it is preferred that: the signal generating device also generates a signal related to a service request for an identified failure location; the transmission device transmits the signal related to the service request to the information management center; the reception device receives a signal related to a servicing cost and a length of servicing time generated at the information management center based upon the signal related to the service request; and the informing device provides information related to the servicing cost and the length of servicing time based upon the signal related to the cost and the length of time which has been received. 
   Also, it is preferred that the signal generating device further generates a signal related to a service request for an identified failure location; the transmission device transmits the signal related to the service request to the information management center; the reception device receives a signal related to a time point at which a service person is expected to arrive at a site generated at the information management center based upon the signal related to the service request; and the informing device provides information related to the time point at which the service person is expected to arrive at the site based upon the signal related to the arrival time point which has been received. 
   A computer program product according to the present invention that can be read by a computer installed in a working machine, contains a working machine failure diagnosis program, and the working machine failure diagnosis program comprises: a signal generation instruction code for generating a signal related to failure information; a transmission instruction code for transmitting the generated signal to an information management center; a reception instruction code for receiving a signal related to a failure diagnosis returned from the information management center in response to the signal transmitted in conformance to the transmission instruction code; and an informing instruction code for providing failure information based upon the received signal. 
   An information management center according to the present invention that exchanges signals with a working machine comprises: a reception device that receives a signal related to failure information transmitted from the working machine; a signal generating device that generates a response signal related to a failure diagnosis in response to the signal; and a transmission device that transmits the response signal to the working machine. 
   A computer program product according to the present invention that can be read by a computer installed at an information management center engaged in signal exchange with a working machine, contains a working machine failure diagnosis program, and the working machine failure diagnosis program comprises: a reception instruction code for receiving a signal related to failure information transmitted from the working machine; a signal generating instruction code for generating a response signal related to a failure diagnosis in response to the signal; and a transmission instruction code for transmitting the response signal to the working machine. 
   A working machine maintenance system according to the present invention comprises: a plurality of working machines; and a center server that manages maintenance on the plurality of working machines by engaging in data exchange through bidirectional communication with each of the plurality of working machines via a communication line, and: the working machines each include an operation data storage device that stores operation data and maintenance data, an operation device operated to enter a maintenance work completion, a data transmission device that transmits the operation data, maintenance work completion data provided through the operation device and the maintenance data to the center server, a data reception device that receives data related to maintenance information transmitted from the center server and a display device at which the maintenance information is displayed; and the center server includes a data reception device that receives the operation data, the maintenance work completion data and the maintenance data that have been transmitted, an operation database in which the operation data are stored, a maintenance database in which the maintenance data are stored, a calculation device that calculates maintenance timing based upon the operation data stored in the operation database and the maintenance data stored in the maintenance database and a data transmission device that transmits data related to the maintenance information including the maintenance timing to a working machine. 
   In this working machine maintenance system, it is preferred that: maintenance work, a completion of which is signaled through an input operation at the operation device, includes failure repair work; and the maintenance data include failure location data indicating a failure location at the working machine. 
   A working machine according to the present invention comprises: a communication device that exchanges information via a communication line through bidirectional communication with a center server managing maintenance on a plurality of working machines; an operation device at which an input operation signaling a maintenance work completion is received; a storage device in which maintenance completion information related to the maintenance work completion is stored; and a control device that transmits the maintenance completion information stored in the storage device to the center server via the communication device when the input operation signaling the maintenance work completion is received at the operation device. 
   In this working machine, it is preferred that: there is further provided a display device; the control device receives maintenance instruction information related to a maintenance instruction transmitted from the center server via the communication line and displays the maintenance instruction information that has been received at the display device. In this case, it is preferred that operation information related to an operation of the working machine is stored in the storage device; and the control device transmits the operation information stored in the storage device to the center server via the communication device with predetermined timing. 
   A computer program product according to the present invention that can be read by a computer installed at a working machine, contains a working machine maintenance program, and the working machine maintenance program comprises: an operation instruction code for receiving an input operation signaling a maintenance work completion at the working machine via an input device; a storage instruction code for storing maintenance completion information related to the maintenance work completion at the working machine into a storage device; and a transmission instruction code for transmitting the maintenance completion information stored in the storage device via a communication device to a center server managing maintenance on a plurality of working machines upon receiving the input operation signaling the maintenance work completion. 
   A center server according to the present invention that manages maintenance on a working machine, comprises: a communication device that exchanges information with a working machine via a communication line through bidirectional communication; a maintenance database in which information related to the maintenance on the working machine is stored; and a control device that receives maintenance completion information related to a maintenance work completion at the working machine transmitted from the working machine via the communication device and stores the received maintenance completion information into the maintenance database. 
   In this center server, it is preferred that: there is further provided an operation database in which operation information related to an operation of the working machine is stored; and the control device receives the operation information transmitted from the working machine via the communication line and stores the received operation information into the operation database. In this case, it is preferred that the control device generates maintenance instruction information related to a maintenance instruction for the working machine based upon the information related to the maintenance on the working machine stored in the maintenance database and the operation information related to the operation of the working machine stored in the operation database and transmits the maintenance instruction information that has been generated to the working machine via the communication device. 
   A computer program product according to the present invention that can be read by a center server managing maintenance on a working machine, contains a working machine maintenance management program, and the working machine maintenance management program comprises: a reception instruction code for receiving maintenance completion information related to a maintenance work completion at the working machine transmitted from the working machine via a communication device; and a storage instruction code for storing the maintenance completion information that has been received into a maintenance database. 
   It is preferred that each of the above computer program products is a recording medium having the working machine failure diagnosis program recorded therein. Or it is preferred that each of the above computer program products is a carrier wave on which the working machine failure diagnosis program is embodied as a data signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of the failure diagnosis system achieved in a first embodiment; 
       FIG. 2  is a side elevation of a hydraulic excavator in which the failure diagnosis system in the first embodiment may be adopted; 
       FIG. 3  presents a flowchart of an example of the information transmission/reception processing that may be executed in the controller of the hydraulic excavator in the first embodiment; 
       FIG. 4  presents a flowchart of an example of the information transmission/reception processing executed in the center server in the first embodiment; 
       FIG. 5  is a diagram of the characteristics of a boom angle sensor; 
       FIG. 6  presents a flowchart of a specific procedure followed in the signal transmission/reception in the failure diagnosis system in the first embodiment; 
       FIG. 7  presents a flowchart of a specific procedure followed in the signal transmission/reception in the failure diagnosis system achieved in a second embodiment; 
       FIG. 8  presents a flowchart of an example of a variation of the procedure shown in  FIG. 7 ; 
       FIG. 9  a system block diagram showing the overall structure of the maintenance system for working machines achieved in a third embodiment; 
       FIG. 10  is a block diagram of the maintenance monitor device mounted at the hydraulic excavator; 
       FIG. 11  is a block diagram showing the structure adopted in, and the processing executed in the essential part of the management server; and 
       FIG. 12  presents a flowchart of the bi-directional data transmission between the maintenance monitor device at the hydraulic excavator and the management server. 
   

   BEST MODE FOR CARRYING OUT OF THE INVENTION 
   First Embodiment 
   In reference to  FIGS. 1˜6 , the first embodiment of the failure diagnosis system according to the present invention is explained. 
     FIG. 1  is a schematic block diagram of the failure diagnosis system achieved in the first embodiment and  FIG. 2  is a side elevation of a hydraulic excavator in which the failure diagnosis system may be adopted. As shown in  FIG. 2 , a hydraulic excavator  1  includes a traveling lower-structure  61 , a swinging upper-structure  62  rotatably mounted on the traveling lower-structure  61  and a work device  63  comprising a boom  63 A, an arm  63 B and a bucket  63 C supported from the swinging upper-structure  62 . A control device  10  and a display device  11  such as a monitor are installed in an operator&#39;s cab  64 . The control device  10  includes a controller  12  and a communication device  13  to which an antenna  14  is connected. A plurality of such hydraulic excavators  1  are deployed on the ground and they exchange information with a center  3  via a communication satellite  2  as shown in  FIG. 1 . 
   Numerous sensors  15  are provided at the hydraulic excavator  1  to detect the engine rotation rate, the hydraulic pump pressure level, the pilot pressure level set in response to an operation of an operating lever, the level of the load applied to an actuator which may be, for instance, a hydraulic cylinder and the like. A command for a signal transmission to the center  3 , a command for image display at the display device  11  and the like are input through the operator&#39;s key operations or the like at an input unit  16 . A warning generator  17  generates a warning based upon a signal provided by a sensor  15  to alert the operator that an abnormality has manifested in the hydraulic excavator. 
   Signals from the sensors  15 , the input unit  16  and the communication device  13  are input to the controller  12  and are stored in a memory  18 . The controller  12  includes a display control unit  19  and a transmission control unit  20 . The display control unit  19  controls the image display at the display device  11 , as shown in, for instance,  FIG. 6  which is to be detailed later by using the signals from the input unit  16  and the communication device  13 . The controller  12  creates transmission data based upon the signals stored in the memory  18  and transmits the transmission data thus prepared to the center  3  with predetermined timing through the processing (see  FIG. 3 ) which is to be explained later. 
   The transmission data created at the controller  12  includes ID data used to identify the model type and the unit number of the hydraulic excavator  1 , data indicating the date of operation and the operating hours of the hydraulic excavator  1 , details of warning generation, the frequency distributions of the output values from the individual sensors relative to the engine rotation rate, details of parts replacement and details of failures. An abnormality signal provided by a sensor  15  enables a detection as to whether or not a failure has occurred. The failure details indicate various abnormalities such as an abnormal voltage output from a sensor  15 , an abnormal engine rotation rate, an abnormal hydraulics pressure level, an abnormal battery charge and an abnormal cooling water temperature, which are provided as coded data. For instance, a failure code “1” is transmitted in the event of a failure at the boom angle sensor, a failure code “2” is transmitted in the event of a failure at an arm angle sensor and a failure code “3” is transmitted in the event of a failure at an electromagnetic valve. 
   These transmission data are received at a communication device  31  of the center  3  via the communication satellite  2  and are then transferred to a management server  32  at the maker to be stored into a database  33 . The management server  32  recognizes any failure in the hydraulic excavator  1  through the processing (see  FIG. 4 ) to be detailed later and transmits specific information to the hydraulic excavator  1 . At the database  33 , the transmission data from the hydraulic excavator  1  are cumulatively stored in correspondence to the individual machine numbers and model types. This makes it possible to keep track of the total length of operating time and the lengths of time over which the various parts have been used for each excavator. In addition, a failure diagnosis procedure for identifying a failure location and the cause of the failure in correspondence to a given failure code is stored in memory at the database  33 . 
   A user&#39;s terminal  34  is connected to the center via, for instance, a telephone line. Thus, the user is able to exchange necessary information with the center  3 . It is to be noted that the user may be a service department or a dealer of the hydraulic excavator maker and the failure information can be transmitted to the nearest service engineer as well. 
   Now, a specific example of the information transmission/reception processing is explained in reference to the flowcharts presented in  FIGS. 3 and 4 . It is to be noted that  FIG. 3  shows the processing executed at the transmission control unit  20 , whereas  FIG. 4  shows the processing executed at the server  32 . These processing programs are stored in a storage device (not shown) within the transmission control unit  20  and a storage device (not shown) at the server  32 . 
   As shown in  FIG. 3 , the signals input from the sensors  15 , the input unit  16  and the communication device  13  are read in step S 1  and these input signals are stored into the memory  18  in step S 2 . Next, a decision is made as to whether or not a transmission command has been issued in step S 3 . A transmission command is output over predetermined time intervals following the work start or in response to an operation of the input unit  16  by the operator. It is to be noted that a transmission command may be output at the completion of the work or at a predetermined time point during the day (e.g., late at night). If an affirmative decision is made in step S 3 , the operation proceeds to step S 4  to prepare the transmission data based upon the data stored in the memory  18 , and the data thus prepared are transmitted in step S 5  before the operation returns to step S 1 . 
   The data transmitted from the communication device  13  are received at the communication device  31  at the center  3 . As shown in  FIG. 4 , the received data are read at the server  32  in step S 11 , and the data are then saved into the database  33  in step S 12 . Next, in step S 13 , a decision is made as to whether or not a failure has occurred by checking for failure codes and if an affirmative decision is made, the operation proceeds to step S 14 , whereas if a negative decision is made, the operation returns to step S 11 . In step S 14 , the database  33  is accessed and transmission data corresponding to the failure code and the received data are prepared. An example of these transmission data is to be explained later in reference to  FIG. 6 . Then, the transmission data are transmitted in step S 15  before the operation returns to step S 11 . 
   Next, the operation of the failure decision-making device that characterizes the first embodiment is explained in further detail. It is to be noted that the following explanation is given on the assumption that the boom angle sensor has output an abnormality signal. 
     FIG. 5  is a diagram of the characteristics of the boom angle sensor  15 . When the sensor  15  is engaged in normal operation, the output voltage fluctuates within the range of 0.5V˜4.5V in correspondence to the boom angle. If the output voltage level becomes equal to or lower than 0.25V or equal to or higher than 4.75V (the shaded areas) the controller  12  judges that an abnormality has occurred in the sensor output value due to disconnection or shorting. In this case, the failure location (the cause of the failure) may be the sensor  15  itself, the harness, the power source, the controller  12  or the like. Accordingly, a failure diagnosis is executed to as explained below to identify the exact failure location. 
     FIG. 6  shows a specific procedure which is taken in the signal transmission/reception between the hydraulic excavator  1  and the center  3 . As the boom angle sensor  15  outputs an abnormality signal (step S 21 ), the warning generator  17  generates a warning and, at the same time, the display control unit  19  generates a control signal to bring up a display of a question as to whether or not a failure diagnosis is to be executed at the display device  11 , as shown in the figure (step S 22 ). If the operator selects “yes” through an operation of the input unit  16  in response to this question, the transmission data (failure data) are transmitted to the center 0.3 together with the failure code “1” through the processing explained earlier (step S 3 -&gt;step S 4 -&gt;step S 5 ). It is to be noted that depending upon the seriousness and the details of the failure, the failure data may be forcibly transmitted to the center  3  regardless of whether the operator selects “yes” or “no”. 
   At the server  32 , the database  33  is accessed through the processing described earlier (step S 13 -&gt;step S 14 -&gt;step S 15 ), the failure diagnosis procedure corresponding to the failure code “1” is read and a first command is transmitted to the hydraulic excavator  1  (step S 23 ). In response to this signal, an electrical conduction check command is brought up on display at the display device  11 , as shown in the figure (step S 24 ). The operator checks the state of electrical conduction at the harness connector by following the instruction on display to verify whether or not the state of electrical conduction is normal. If “abnormal” is selected through an operation of the input unit  16 , the server  32  accesses the database  33 , identifies the cause of the failure by using the transmitted information and sends information indicating the identified cause to the excavator  1  (step S 25 ) As a result, information such as that shown in the figure is brought up on display at the display device  11  (step S 26 ) so that the operator is able to identify the cause of the failure detected in the sensor  15  as a harness malfunction. 
   If, on the other hand, “normal” is selected through an operation of the input unit  16  in step S 24 , the server  32  transmits a second command to the excavator  1  (step S 27 ). In response to this signal, a display of a resistance value measurement command is brought up at the display device  11  as shown in the figure (step S 28 ). The operator follows this instruction and measures the resistance value at the connector of the sensor  15  to verify whether or not the resistance value is in the normal range. Then, if “abnormal” is selected, the server  32  accesses the database  33  to identify the cause of the failure and sends information indicating the identified cause to the excavator  1  (step S 29 ). As a result, information such as that shown in the figure is brought up on display at the display device  11  (step S 30 ) so that the operator can identify the failure as a malfunction in the sensor  15  itself. 
   If “normal” is selected in step S 28 , the server  32  accesses the database  33 , identifies the cause of the failure based upon the accumulated information and sends information indicating the identified caused to the excavator  1  (step S 31 ). 
   In this case, the cause of the failure is judged to be a malfunction of the controller  12  and information indicating the cause is brought up at the display device  11  as shown in the figure (step S 32 ). Through the processing described above, the location of the failure can be identified in the event of an abnormality detected in the boom angle sensor. 
   It is to be noted that while an explanation is given above on an example in which a-failure diagnosis is executed for the boom angle sensor  15 , a failure diagnosis can be executed in a similar manner for an electromagnetic proportional valve as well. In the latter case, if the value which is actually detected is equal to or higher than 3 MPa when the command value for the electromagnetic proportional valve driven by an electric lever is, for instance, equal to or lower than 1 MPa, it may be judged that a failure has occurred in the electromagnetic proportional valve and the failure code “3” may be transmitted accordingly. Then, in response to a command issued by the server  32 , the operator should take an appropriate action such as checking the state of electrical conduction at the harness. 
   As described above, when the first embodiment, in which signals are exchanged between the hydraulic excavator  1  and the server  32  via the communication satellite  2  and information with regard to a failure at the excavator  1  is displayed at the display device  11  in a dialog format is adopted, the operator is able to ascertain the location of the failure with ease. As a result, the operator is able to take appropriate post-failure action. In addition, since a failure diagnosis is started in response to the output of an abnormality signal from a sensor  15 , the failure diagnosis is performed in a timely manner. Furthermore, since the server  32  accesses the database  33  to identify the location of the failure, it is not necessary to store in memory a large volume of data at the excavator and thus, it is possible to utilize the available storage capacity at the excavator in an efficient manner. Moreover, the failure data are coded and thus, the data structure is simpler. 
   Second Embodiment 
   The second embodiment of the present invention is now explained in reference to  FIGS. 7 and 8 . While the image displayed at the display device  11  is automatically switched in the event of a failure at a sensor  15  and the operation enters the failure diagnosis mode in the first embodiment, the operation enters the failure diagnosis mode in response to a menu selection operation performed by the operator in the second embodiment. The following explanation focuses on the difference from the first embodiment. 
   The second embodiment differs from the first embodiment in the specific procedure followed in the signal to transmission/reception between the hydraulic excavator  1  and the center  3 . If any problem occurs while driving the hydraulic excavator  1 , the operator selects the failure diagnosis mode by operating the input unit  16 . In response, an initial screen such as that shown in  FIG. 7 , for instance, is the brought up at the display device  11  (step S 41 ). In this example, “not able to move the front” is selected from the display screen. At the database  33 , the procedures corresponding to various selection signals are stored in advance, and the server  32  reads the procedure corresponding to the specific selection signal from the database  33  and transmits a first command to the excavator  1  (step S 42 ). In response, a question such as that shown in the figure is brought up on display at the display device  11  (step S 43 ). 
   If “boom-up” is selected as the answer to this question, the server  32  transmits a second command corresponding to the selection signal (step S 44 ) and the command is displayed as shown in the figure at the display device  11  (step S 45 ). As the operator performs a boom-up operation in response to this command, the values of the detected pump pressure and pilot pressure during the boom-up operation are transmitted to the server  32 . The server  32  makes a decision as to whether or not the transmitted detection values are in normal ranges (step S 46 ) and transmits a third command if detected values are in abnormal ranges, i.e., if they are much lower than the preset values. In response, the command is displayed as shown in the figure at the display device  11  (step S 48 ). If the operator selects “normal” upon checking the harness in response to this command, the server  32  identifies the location of the failure based upon the accumulated information (step S 49 ). As a result, the location of the failure and a service contact are brought up on display together as shown in the figure at the display device  11  (step S 50 ). 
   If, on the other hand, it is decided in step S 46  that the values of the detected pump pressure and pilot pressure are in the normal ranges, the server  32  transmits a fourth command (step S 51 ) and the command is displayed at the display device  11  as shown in the figure (step S 52 ). If the operator selects “normal” upon checking for any oil leak in response to this command, the server  32  identifies the location of the failure based upon the accumulated information (step S 53 ). As a result, the location of the failure and a service contact are brought up on display together as shown in the figure at the display device  11  (step S 54 ). 
   While the location of the failure and the service contact are displayed in step S 50  and step S 54  as described above, a service person may be contacted through a question and answer format as shown in  FIG. 8 , instead. For instance, after the location of the failure is identified as the electromagnetic valve, information such as that shown in  FIG. 8  is brought upon display at the display device  11  (step S 55 ). If “contact online” is selected at this point, the server  32  accesses the database  33  and calculates the price of the replacement electromagnetic valve, the length of the standard labor time and the corresponding repair fee (step S 56 A). 
   In this system, each service engineer enters his work schedule for the day in advance by using his own personal computer or the like, and the schedule information is transmitted to the center  3  where it is stored into the database  33 . In addition, the hydraulic excavator  1  is mounted with a position measuring instrument such as a GPS unit and thus, information indicating the current position of the hydraulic excavator  1  is transmitted to the center  3  in real time. Based upon the information, the server  32  determines the closest service department to the work site and the service engineer who can most quickly be dispatched to the site and transmits information with regard to the service request to the service engineer via the service department or by bypassing the service department. The service engineer, in turn, sends a response to the information indicating whether or not he is able to provide his service and the estimated time of arrival at the work site to the server  32  (step S 56 B). 
   The information obtained in steps S 56 A and S 56 B is transmitted to the excavator  1  where the information is brought up on display at the display device  11  as shown in the figure (step S 57 ). Accordingly, the operator verifies the length of the labor time, the fee and the like and makes a decision as to whether or not a repair order is to be placed. If “yes” (the repair is ordered) is selected in step S 57 , this command is relayed to the service engineer via the center and the service engineer is dispatched to the site (step S 58 ). 
   As explained above, in the second embodiment in which the failure diagnosis mode is selected through a menu operation by the operator, the location where a problem has occurred can be identified any time at the operator&#39;s request. In the event of a failure, a service request can be issued through a selection operation by the operator carried out in a dialogue format and thus, he does not need to go through the traditional, time-consuming process of repair order placement. In addition, since information such as the parts price, the length of time required for the repair work and the estimated time of arrival of the service engineer becomes instantly available, the efficiency and the operability are improved. 
   It is to be noted that while the information regarding a failure in the hydraulic excavator  1  is displayed at the display device  11  to alert the operator in the embodiment, the operator may be provided with the information through an audio message instead. In addition, while signals are exchanged over a plurality of times between the hydraulic excavator  1  and the center  3  in the processing shown in  FIGS. 6˜8 , signals may be transmitted once each from the hydraulic excavator  1  and the center  3  instead. While the present invention is adopted in conjunction with hydraulic excavators in the embodiment described above, it may instead be adopted in other construction machines. 
   Third Embodiment 
     FIG. 9  shows the overall structure of the maintenance system for working machines achieved in the third embodiment. Three hydraulic excavators  111 A,  111 B and  111 C are shown in the figure as an example of working machines subscribing to the maintenance service. However, the maintenance work may be performed on working machines other than hydraulic excavators. While numerous hydraulic excavators are managed through this maintenance system for upkeep, management and maintenance in reality, only three hydraulic excavators  111 A˜ 111 C, i.e., excavator  1 , excavator  2  and excavator  3  are shown in the figure to simplify the explanation. These hydraulic excavators are assigned to individual work sites. The hydraulic excavators  111 A˜ 111 C, which are managed through the maintenance system achieved in the embodiment as detailed later include maintenance monitor devices adopting structures identical to one another. The hydraulic excavators  111 A˜ 111 C are each mounted with a control device constituted of a computer, and the control device includes a communication device, an operation control unit, an arithmetic processing unit, a storage unit and the like. These control devices enable the hydraulic excavators  111 A˜ 111 C to exchange information with an external partner via an electrical communication line. The maintenance monitor devices mentioned earlier are each realized in the form of a control device adopting the structure described above. 
   A management server (or a center server)  112  is provided to manage the maintenance of the plurality of the hydraulic excavators  111 A˜ 111 C. The management server  112  is installed at a base station, whereas the hydraulic excavators  111 A˜ 111 C are assigned to work sites at remote locations. The management server  112  is operated by the maker, a rental company, a sales company, a maintenance management company or the like. The management server  112  comprises a computer  113 , various types of input devices  114 , a display device (display)  115 , an operation database  116 , in which operation data are stored, and a maintenance database  117 , in which maintenance data (data on regular inspections, failure repair data, data on replacement of parts and consumables) are stored. The computer  113  at the management server  112  includes functional units such as the communication device and the arithmetic processing unit and exchanges information (commands, data and the like) with each of the hydraulic excavators  111 A˜ 111 C at remote locations via the electrical communication line. 
   The electrical communication line (a data communication path) connects the hydraulic excavators  111 A˜ 111 C with the management server  112 . The electrical communication line is constituted of a communication satellite  118 , a ground station  119  and a public line or the Internet  120 . The hydraulic excavators  111 A˜ 111 C and the management server  112  engage in bidirectional communication through their communication devices and also via the electrical communication line adopting the structure described above. 
   Arrows  121 ,  122 ,  123  and  124  in  FIG. 9  indicate various states in which communication is in progress. However, these arrows simply represent an example. 
   The arrow  121  indicates a state in which operation data  125  are transmitted from the hydraulic excavator  111 A to the management server  112  via the communication satellite  118 , the ground station  119  and the like. The operation data  125 , shown as a block of data, indicate the frequency distributions of the engine rotation rate, the hydraulic operating fluid temperature, the radiator water temperature, the pump pressure and the like at the hydraulic excavator  11 A. The operation data  125 , which are obtained at the control device through various operation sensors to ascertain the operating state of the hydraulic excavator  111 A while it is engaged in work, are stored in the storage unit. The operation data are collected and saved at the maintenance monitor device mentioned earlier. The operation data are transmitted by the control device and the communication device at the hydraulic excavator  111 A on a regular basis or as necessary to the management server  112  where they are recorded into the operation database  116 . 
   The arrow  122  indicates a state in which a command related to maintenance is transmitted from the management server  112  to the hydraulic excavator  111 B. The contents of this maintenance command are displayed as a message, e.g., “change oil”, at an on-vehicle display device  126  provided inside the operators cab of the hydraulic excavator  111 B. In  FIG. 9 , the on-vehicle display device  126  is shown in an enlargement for emphasis. 
   The arrow  123  indicates a state  129  in which a maintenance completion signal is transmitted to the management server  112  in response to an ON operation of a maintenance complete switch  127  at the hydraulic excavator  111 C by a service engineer or operator  128 . The service engineer performs maintenance work related to the items displayed at the on-vehicle display device  126 , for instance, and presses the maintenance complete switch  127  when the work is completed. As a result, the length of operating time having elapsed up to the work completion and the maintenance work items are automatically transmitted to the management server  112  and the transmitted contents are recorded into the maintenance database  117  at the management server  112 . 
   As described above, necessary data and commands are exchanged through the bidirectional communication between the individual hydraulic excavators  111 A˜ 111 C assigned at the various work sites and the management server  112 . 
   In addition, a user  131  can access the management server  112  via the Internet  130  by using an Internet terminal device  132 . The user  131  is a party involved in the operation of one of the hydraulic excavators  111 A˜ 111 C. The user  131  accesses the homepage of the management server  112  that provides maintenance information, receives permission for information access by entering his ID and password and obtains the maintenance information on the relevant hydraulic excavator or the like. 
   Now, in reference to  FIG. 10 , a specific structure that may be adopted in the maintenance monitor devices provided in the hydraulic excavators  111 A˜ 111 C is explained. 
   A maintenance monitor device  141  is realized in the form of a control device  142  constituted of a computer. The control device  142  comprises a CPU  143 , a storage unit (memory)  144 , a sensor input interface (I/F)  145 , a display interface (I/F)  146  and a communication interface (I/F)  147 . Signals indicating the operating state of the hydraulic excavator detected by operation sensors  148  provided at the various mechanical components including the engine and the hydraulic fuel supply system are input to the CPU  143  via the sensor input interface  145 . The CPU  143  stores operation data based upon the various operation signals input thereto into the storage unit  144 . At the storage unit  144 , a program and data which enable the execution of the various types of processing are stored. The data stored at the storage unit  144  include the data indicating the machine number and the model type, maintenance data and maintenance information in addition to the operation data described above. The maintenance complete switch  127  explained earlier is provided at the operator&#39;s cab of the hydraulic excavator. An ON operation signal generated at the maintenance complete switch  127  is input to the CPU  143 . The control device  142  includes a display device  149 . This display device  149  corresponds to the on-vehicle display device shown in  FIG. 9 . Display data are transmitted from the CPU  143  via the display interface  146  and maintenance related information is displayed at the screen of the display device  149 . The maintenance monitor device  141  includes a communication device  150 . The communication device  150  constitutes a data communication terminal. Various types of data are exchanged between the control device  142  and the management server  112  via the communication device  150 . The communication device  150  is connected to the CPU  143  via the communication interface  147 . 
   Details of the processing executed by the maintenance monitor device  141  adopting the structure described above are provided below in relation to the communication with the management server  112 . 
   Next, in reference to  FIG. 11 , the structure of the management server  112  and the essential processing executed in the management server  112  are explained in detail. The management server  112  in  FIG. 11  includes data storage units, i.e. the operation database (operation DB)  116  and the maintenance database (maintenance DB)  117 , as described earlier. The various types of data transmitted from the hydraulic excavators  111 A˜ 111 C to the management server  112  via the electrical communication line are received at a communication reception unit  151  of the management server  112 . The operation data are then passed through the communication reception unit  151  and stored (recorded) in the operation database  116 . In the operation database  116 , each set of operation data is recorded as a file  116   a  corresponding to a specific machine number and model type. In addition, each set of maintenance data is recorded at the maintenance database  117  as a file  117   a  corresponding to a specific machine number and model type. The computer  113  of the management server  112  includes a maintenance timing calculation unit  152  as a functional means. The maintenance timing calculation unit  152  calculates the correct timing with which maintenance (repairs, parts replacement) should be performed on various parts (maintenance requiring parts) of the working machines in correspondence to the individual machine numbers a model types based upon maintenance criteria obtained through statistical processing of the operation data and the maintenance data from numerous hydraulic excavators. The data indicating the maintenance timing for each machine number and model type calculated at the maintenance timing calculation unit  152  are transmitted to the hydraulic excavator classified under the corresponding machine number and model type through a communication transmission unit  153  and then via the electric communication circuit explained earlier. 
   Next, details of the data transmission/reception processing achieved through the bidirectional communication between the maintenance monitor device  141  provided at the individual hydraulic excavators  111 A˜ 111 C and the management server  112  are explained.  FIG. 12  presents a flowchart of the bidirectional data exchange between the maintenance monitor device of a hydraulic excavator and the management server. The programs for executing the processing are stored in advance at storage devices (not shown) within the maintenance monitor device  141  and the management server  112 . 
   At each hydraulic excavator, its maintenance monitor device  141  stores with a predetermined timing the operation data indicating the operating state of the mechanical parts engaged in operation on a daily basis (step S 111 ). In the operation data recording processing, the CPU  143  takes in operation signals via the various operation sensors  148  mentioned earlier and stores them as operation data into the storage unit  144 . Information indicating the model type and machine number is appended to the operation data stored in the storage unit  144 . As the operation data are accumulated over a specific length of time at the storage unit  144 , the CPU.  143  executes processing for transmitting the operation data stored in the storage unit  144  to the management server  112  on a regular basis (e.g., every 100 engine operating hours) (step S 112 ). The operation data are transmitted in response to the processing executed by the CPU  143  via the communication interface  147 , the communication device  150  and the electrical communication line constituted of the communication satellite  118  and the like (through a transmission procedure P 111 ). The operation data being transmitted are appended with the data indicating the model type and machine number of the corresponding hydraulic excavator. 
   Upon receiving the operation data transmitted from the maintenance monitor device  141  of the hydraulic excavator (through the transmission procedure P 111 ) at the communication reception unit  151 , the management server  112  stores the received operation data in correspondence to the model type and machine number into the operation data base  116  (step S 121 ). Next, the maintenance timing calculation unit  152  calculates the maintenance timing for the individual maintenance-requiring parts by using a formula conforming to the predetermined criteria (step S 122 ). During the maintenance timing calculation processing, the processing details recorded in the maintenance data base  117  are referenced for the calculation. Each set of maintenance timing data is calculated in correspondence to a given maintenance requiring part. The maintenance timing data obtained through the maintenance timing calculation processing (step S 122 ) are transmitted as maintenance information to the maintenance monitor device  141  of the corresponding hydraulic excavator (step S 123 ) via the communication transmission unit  153  together with a corresponding command (message). The maintenance information is transmitted from the management server  112  to the maintenance monitor device  141  through the electrical communication line mentioned earlier (through a transmission procedure P 112 ). 
   At the maintenance monitor device  141 , the maintenance information transmitted from the management server  112  is taken into the CPU  143  via the communication device  150  and the communication interface  147 , and the CPU  143  displays the maintenance information at the display device  149  via the display interface  146  (step S 113 ). An example of a display mode that may be assumed at the display device  149  is shown at the on-vehicle display device  126  of the hydraulic excavator  111 B in  FIG. 9 . 
   Subsequently, a service engineer performs maintenance work on the hydraulic excavator in conformance to the maintenance information provided by the management server  112 . Under normal circumstances, the operator of the hydraulic excavator checks the contents of the display brought up at the display device  149 , verifies the items to be serviced and the timing of the maintenance and places a request to the service engineer (or a maintenance technician) for maintenance service. The service engineer performs the maintenance work as indicated at the display device  149  and once the maintenance work is completed (step S 114 ), the service engineer turns on the maintenance complete switch  127  to signal work completion. In response to the ON operation of the maintenance complete switch  127 , an ON signal is input to the CPU  143  and thus, the CPU  143  executes work complete switch detection processing (step S 115 ). Following the work complete switch detection processing, the CPU  143  executes processing for transmitting the maintenance data to the management server  112  (step S 116 ) During the maintenance data transmission processing, the data including the model type and machine number, the maintenance item and the length of operating time are read from the storage unit  144  and the data thus read out are transmitted to the management server  112  via the communication interface  147 , the communication device  150  and the electrical communication line (through transmission procedure P 113 ). At the management server  112 , the maintenance data that have been received are recorded into the maintenance database  117 . The recorded maintenance data are incorporated with the basic data for the next maintenance timing calculation processing (step S 122 ) to be used for the next maintenance forecast calculation. 
   In the structure described above, a plurality of sets of maintenance information may be brought up on display at the display device  149  of the maintenance monitor device  141 . In this case, maintenance work is performed in correspondence to each of the plurality of sets of maintenance information on display. An ON operation of the maintenance complete switch  127  to signal a work completion may be performed upon completion of each maintenance work operation or it may be performed upon completion of the entire series of maintenance work. 
   Failure repair work may be executed during the maintenance work the completion of which is signaled through the maintenance complete switch  127  in the structure described above, and accordingly, the maintenance data may contain failure location data indicating the location of a failure in the hydraulic excavator. When a failure occurs at the hydraulic excavator, requiring repair work other than the maintenance work which is executed as directed by the management server  112 , information related to the failure repair can be transmitted to the management server  112  by using the maintenance complete switch  127  and the failure repair information can be recorded into the maintenance database. 
   The data exchange achieved through the bidirectional communication between the maintenance monitor device  141  and the management server  112  is performed individually between the each of the hydraulic excavators  111 A˜ 111 C and the management server  112 . 
   By adopting the third embodiment explained above, in which bidirectional communication is achieved between the center server and each of a plurality of working machines through the electrical communication line constituted of a communication satellite, the Internet and the like, a maintenance monitor device that collects maintenance data necessary for the maintenance management and stores the maintenance data in a storage unit is provided in each working machine and the maintenance data are automatically transmitted to the center server as an operating means for signaling a work completion is operated upon the completion of the maintenance work, the manual input operation normally performed by the service engineer or the like in the related art is eliminated and a higher degree of reliability is achieved through the automatic transmission of the maintenance data. 
   In addition, the center server, which prepares maintenance information indicating a specific maintenance-requiring part and maintenance timing for each working machine based upon the operation data and the maintenance data stored in the database and transmits the maintenance information thus prepared to the corresponding working machine to be referenced by the operator, is enabled to execute the maintenance work with reliability. 
   While an explanation is given above in reference to the embodiments on an example in which the present invention is adopted in conjunction with hydraulic excavators, the present invention is not limited to this example. The present invention may instead be adopted in conjunction with cranes or other types of construction working machines (construction machinery). In addition, the present invention may be adopted in conjunction with working machines other than construction working machines, as long the working machines are engaged in operation at work sites and a management center can be connected with the working machines through a communication line which enables bidirectional communication. 
   While an explanation is given above in reference to the embodiments on an example in which transmission/reception is achieved through a communication satellite, the application of the present invention is not restricted by these particulars. For instance, data transmission/reception may be achieved by using a mobile communication system such as a mobile telephone (a cellular phone) or a PHS telephone, or it may be achieved by using another wireless system as well. 
   While an explanation is given above in reference to the embodiments on an example in which the programs executed by the working machines and the management server at the center are stored in advance in the internal storage devices, the present invention is not limited to this example. For instance, the programs may be provided in recording media such as CD-ROMs  21  and  35  in  FIG. 1 . Alternatively, the programs may be provided by a program server connected via the Internet. Furthermore, the working machine program may be provided by the management server in  FIG. 1  or  FIG. 6 . When the programs are provided via the Internet and a communication satellite, they should be embodied as data signals on carrier waves which are transmitted via a communication-line. In short, the programs can be distributed as a computer readable computer program product assuming any of various modes including a recording medium and a carrier wave. 
   The structural features, the shapes, the dimensions and the positional relationships explained in reference to the embodiments above represent an approximate example provided to facilitate understanding and implementation of the present invention and the numerical values referred to above also represent examples. Accordingly, the present invention is not limited to the embodiments explained above and various modifications may be realized without departing from the scope of the technical concept of the present invention.