Patent Publication Number: US-11041290-B2

Title: Locking system for a work machine

Description:
TECHNICAL FIELD 
     The present invention relates to a work machine capable of switching via a gate lock lever whether it is allowed to operate actuators. 
     BACKGROUND ART 
     Patent Literature 1 describes a work vehicle that enables prevention of unexpected operation of actuators due to unintended operation at the time of gate lock lever switching. The work vehicle described in Patent Literature 1 switches a lock valve from a locked state to a released state if a lock member is switched from a lock position to a release position, and switches the lock valve to the locked state in a case where a pilot pressure has become equal to or higher than a predetermined pressure in a predetermined length of time after the lock member is switched to the release position. 
     CITATION LIST 
     Patent Literature 
     PATENT LITERATURE 1: Japanese Patent No. 5467176 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the work vehicle described in Patent Literature 1, whether or not unintended operation has occurred is detected while the lock valve is kept in the released state, and the lock valve is switched to the locked state again after unintended operation is detected. However, an inertial force is applied to an actuator having started operating, and so there is a possibility that even if the lock valve is switched to the locked state, the actuator does not stop immediately. 
     The present invention has been contrived in view of the circumstance described above, and an object thereof is to provide a work machine that can stop unexpected operation of actuators faster than it actually occurs even if unintended operation occurs at the time of gate lock lever switching that leads to such unexpected operation. 
     Solution to Problem 
     In order to achieve the object, in a work machine of the present invention including: an engine; a hydraulic pump driven by the engine; an actuator driven by a hydraulic fluid delivered by the hydraulic pump; a directional control valve that is provided between the hydraulic pump and the actuator, and controls an operation direction of the actuator and a speed of the actuator; an actuator operation device that operates the actuator; a pilot valve that outputs, to the directional control valve and as an operation signal, a pilot pressure according to an operation amount of the actuator operation device; a lock operation device that can be operated to a permission position for permitting an entrance of an operator to an operator&#39;s seat, and a prohibition position for prohibiting an entrance of the operator to the operator&#39;s seat; a lock valve that is switched to a lock position for interrupting a supply of the hydraulic fluid to the pilot valve in a case where the lock operation device is operated to the permission position, and is switched to a release position for supplying the hydraulic fluid to the pilot valve in a case where the lock operation device is operated to the prohibition position; a pressure sensor that detects the pilot pressure; and a controller that controls a switch position of the lock valve, the controller switches the lock valve from the lock position to the release position in a case where the lock operation device is operated from the permission position to the prohibition position; decides, on the basis of a result of the detection by the pressure sensor, whether or not a pilot hydraulic fluid has been output from the pilot valve until first time elapses after the lock valve is switched to the release position; keeps the lock valve at the lock position if it is decided that the pilot hydraulic fluid has been output until the first time elapses; and switches the lock valve from the lock position to the release position if it is decided that the pilot hydraulic fluid has not been output until the first time elapses, and second time elapses. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to stop unexpected operation of actuators faster than it actually occurs even if unintended operation occurs at the time of gate lock lever switching that leads to such unexpected operation. Note that problems, configurations and effects other than those described above are made apparent by the following explanation of an embodiment. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a hydraulic excavator that is a representative example of a work machine according to the present invention. 
         FIG. 2  is a figure illustrating the schematic configuration of a hydraulic circuit included in the hydraulic excavator. 
         FIG. 3  is a block diagram illustrating the configuration of a controller included in the hydraulic excavator. 
         FIG. 4  is a flowchart of an unintended-operation control process executed by the controller. 
         FIG. 5  is a time chart illustrating temporal changes of the position of a gate lock lever, the position of a lock valve, operation of work levers, a parking release pressure, operation of travel levers, and a travel pilot pressure. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An embodiment of a work machine according to the present invention is explained by using the drawings.  FIG. 1  is a side view of a hydraulic excavator  1  that is a representative example of a work machine according to the present invention.  FIG. 2  is a figure illustrating the schematic configuration of a hydraulic circuit included in the hydraulic excavator  1 . Note that unless otherwise noted particularly, the front, rear, left and right directions in the present specification are relative to the viewpoint of an operator who gets on, and operates the hydraulic excavator  1 . In addition, specific examples of the work machine are not limited to the hydraulic excavator  1 , but may be a dump truck, a motor grader, a wheel loader, and the like. 
     The hydraulic excavator  1  includes a undercarriage  2 , and an upperstructure  3  supported by the undercarriage  2 . The undercarriage  2  includes a pair of left and right crawlers  8 . The pair of left and right crawlers  8  rotate independently by driving wheels  8   c  driven by hydraulic motors  8   a  and  8   b  (see  FIG. 2 ). Thereby, the hydraulic excavator  1  can move forward and backward, and make turns. 
     The upperstructure  3  is supported by the undercarriage  2  such that the upperstructure  3  can be swung by a swing motor  3   a  (see  FIG. 2 ). The upperstructure  3  includes: a swing frame  5  that serves as a base; a cab (operator&#39;s seat)  7  arranged on the front left side of the swing frame  5 ; a front work device  4  attached vertically rotatably to the middle on the front side of the swing frame  5 ; a counter weight  6  arranged on the rear side of the swing frame  5 ; and an engine  10  that generates drive force for operating the hydraulic excavator  1 . 
     The front work device  4  includes: a boom  4   a  supported by the upperstructure  3  such that the boom  4   a  can face upward and downward; an arm  4   b  supported by the tip of the boom  4   a  such that the arm  4   b  can oscillate; a bucket  4   c  supported by the tip of the arm  4   b  such that the bucket  4   c  can oscillate; and hydraulic cylinders (actuators)  4   d  to  4   f  that drive the boom  4   a , the arm  4   b , and the bucket  4   c . That is, the boom  4   a  is directly supported by the upperstructure  3 , and the arm  4   b  and the bucket  4   c  are indirectly supported by the upperstructure  3 . The counter weight  6  is for counterbalancing the weight of the front work device  4 , and is an arc-shaped heavy object. 
     The cab  7  has an internal space formed therein. An operator who operates the hydraulic excavator  1  gets in the internal space. The internal space of the cab  7  has operation devices (a steering, pedals, levers, switches, etc.) arranged therein. The operator operates the operation devices to give instructions to operate the hydraulic excavator  1 . That is, by the operation devices being operated by the operator who got in the cab  7 , the hydraulic excavator  1  is operated. The operation devices include actuator operation devices for causing the undercarriage  2  to travel, swinging the upperstructure  3  and operating the front work device  4 , and lock operation devices that lock and unlock operation of the hydraulic excavator  1 . 
     As illustrated in  FIG. 2 , the actuator operation devices include: travel levers (travel operation devices)  11  and  12  that operate the pair of left and right crawlers  8 , respectively; a boom lever  13  that operates the boom  4   a ; an arm lever  14  that operates the arm  4   b ; a bucket lever  15  that operates the bucket  4   c ; and a swing lever  16  that swings the upperstructure  3 . The lock operation devices include a gate lock lever  17  that switches the position of a lock valve  31  mentioned below. 
     Note that the forms of the actuator operation devices, and the lock operation devices are not limited to lever forms, but may be steering forms, pedal forms, switch forms, button forms, or the like. In addition, in the following explanation, the boom lever  13 , the arm lever  14 , the bucket lever  15 , and the swing lever  16  are in some cases collectively denoted as “work levers  13  to  16 .” 
     The actuator operation devices are connected to pilot valves  21 ,  22 ,  23 ,  24 ,  25  and  26 . The pilot valves  21  to  26  output hydraulic fluids pressurized and fed by a hydraulic pump (pilot pump)  33  driven by the engine  10  from a hydraulic fluid tank  32  to a hydraulic control circuit  34  as pilot hydraulic fluids for operating the corresponding actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b . The flow rates of the pilot hydraulic fluids change in accordance with operation amounts of corresponding actuator control devices. The pressures (pilot pressures) of the pilot hydraulic fluids are one example of operation signals. 
     More specifically, the pilot valves  21  and  22  output pilot hydraulic fluids for driving the hydraulic motors  8   a  and  8   b  in accordance with operation amounts of the travel levers  11  and  12 . The pilot valve  23  outputs a pilot hydraulic fluid for driving the boom cylinder  4   d  in accordance with an operation amount of the boom lever  13 . The pilot valve  24  outputs a pilot hydraulic fluid for driving the arm cylinder  4   e  in accordance with an operation amount of the arm lever  14 . The pilot valve  25  outputs a pilot hydraulic fluid for driving the bucket cylinder  4   f  in accordance with an operation amount of the bucket lever  15 . The pilot valve  26  outputs a pilot hydraulic fluid for driving the swing motor  3   a  in accordance with an operation amount of the swing lever  16 . 
     The gate lock lever  17  is configured such that an operator can switch the gate lock lever  17  to a permission position for restricting operation of the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b , and permitting an entrance of the operator to the cab  7 , and a prohibition position for permitting operation of the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b , and prohibiting an entrance of the operator to the cab  7 . The gate lock lever  17  outputs, to a controller  50  (see  FIG. 3 ), a release signal when the gate lock lever  17  is at the prohibition position, for example. 
     The gate lock lever  17  is arranged between the entrance and seat of the cab  7 , for example. Then, the gate lock lever  17  may be configured such that when the gate lock lever  17  is at the permission position, the operator is not prevented from getting in or out of the cab  7 , and when the gate lock lever  17  is at the prohibition position, the operator is prevented from getting in or out of the cab  7 . Thereby, it is possible to lower the possibility that an operator leaves the cab  7  while keeping the gate lock lever  17  at the prohibition position. 
     The hydraulic control circuit  34  supplies, to the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b , a hydraulic fluid delivered by a hydraulic pump  330  driven by the engine  10  in accordance with the pilot hydraulic fluids supplied from the pilot valves  21  to  26 . The hydraulic control circuit  34  includes directional control valves that are provided between the hydraulic pump  33 , and the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b , for example, and switch the supply amounts and supply directions of the hydraulic fluid in accordance with the pilot hydraulic fluids. A plurality of the directional control valves are provided corresponding to the individual actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b , control the speeds of the corresponding actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b  in accordance with the supply amount of the hydraulic fluid, and control the operation directions of the corresponding actuator  3   a ,  4   d  to  4   f , and  8   a  to  8   b  in accordance with the supply direction of the hydraulic fluid. The specific configuration of the hydraulic control circuit  34  is already well-known, and so detailed explanation is omitted. 
     The lock valve  31  is a solenoid valve switched to a lock position and a release position in accordance with control by the controller  50 . When the lock valve  31  is at the lock position, the supply of the hydraulic fluid from the hydraulic pump  33  to the pilot valves  21  to  26  is interrupted. On the other hand, when the lock valve  31  is at the release position, the supply of the hydraulic fluid from the hydraulic pump  33  to the pilot valves  21  to  26  is permitted. The lock valve  31  is configured such that, for example, the lock valve  31  is initially at the lock position, and the lock valve  31  is switched to the release position only while a release signal is being output from the gate lock lever  17 , and returns to the lock position if the output of the release signal is stopped. 
     That is, when the gate lock lever  17  is at the permission position (the lock valve  31  is at the lock position), no pilot hydraulic fluids are output from the pilot valve  21  to  26  even if an actuator operation device is operated. In other words, when the gate lock lever  17  is at the permission position (the lock valve  31  is at the lock position), the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b  are not driven even if an actuator operation device is operated. 
     On the other hand, when the gate lock lever  17  is at the prohibition position (the lock valve  31  is at the release position), a pilot hydraulic fluid is output from the pilot valve  21  to  26  if an actuator operation device is operated. That is, when the gate lock lever  17  is at the prohibition position (the lock valve  31  is at the release position), the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b  are driven in accordance with operation of an actuator operation device. 
     The hydraulic control circuit  34  is connected with a swing brake  35  that restricts and permits the swing of the upperstructure  3 . The swing brake  35  includes, for example, a brake pad  36  that brakes a rotation axis  3   b  of the upperstructure  3 , and a cylinder  37  that makes the brake pad  36  in and out of contact with the rotation axis  3   b . The swing brake  35  is configured such that, by a parking release hydraulic fluid supplied from the hydraulic control circuit  34 , the swing brake  35  can be switched to a state where it restricts the swing of the upperstructure  3  and to a state where it permits the swing of the upperstructure  3 . 
     The cylinder  37  restricts the swing of the upperstructure  3  by causing the brake pad  36  to abut against the rotation axis  3   b  by using the urging force of a coil spring  38  that is one example of an urging member. In addition, if the cylinder  37  receives, at the rod chamber, the supply of the parking release hydraulic fluid from the hydraulic control circuit  34 , the cylinder  37  separates the brake pad  36  from the rotation axis  3   b  against the urging force of the coil spring  38 , and permits the swing of the upperstructure  3 . Furthermore, if the cylinder  37  stops receiving the supply of the parking release hydraulic fluid from the hydraulic control circuit  34 , the cylinder  37  causes the brake pad  36  to abut against the rotation axis  3   b  again by using the urging force of the coil spring  38 , and restricts the swing of the upperstructure  3 . 
     The swing brake  35  is a so-called negative brake that prevents an unintended swing of the upperstructure  3  while the hydraulic excavator  1  is stopped. On the other hand, if the upperstructure  3  or the front work device  4  is operated while the swing of the upperstructure  3  is restricted, the upperstructure  3  receives an excessive load. In view of this, when the upperstructure  3  or the front work device  4  is operated, the swing brake  35  needs to be released. 
     In view of this, the hydraulic control circuit  34  supplies the parking release hydraulic fluid to the cylinder  37  while the gate lock lever  17  is at the prohibition position, and at least one of the work levers  13  to  16  is being operated (i.e. while the pilot hydraulic fluid is being output from at least one of the pilot valves  23  to  26 ). That is, the swing brake  35  permits the swing of the upperstructure  3  while the pilot hydraulic fluid is being supplied from at least one of the pilot valves  23  to  26 . 
     On the other hand, the hydraulic control circuit  34  stops the supply of the parking release hydraulic fluid while the gate lock lever  17  is at the permission position or while the gate lock lever  17  is at the prohibition position, and none of the work levers  13  to  16  is being operated (i.e. while the pilot hydraulic fluid is not output from any of the pilot valves  23  to  26 ). That is, the swing brake  35  restricts the swing of the upperstructure  3  while the pilot hydraulic fluid is not output from any of the pilot valves  23  to  26 . 
     In addition, in order to release the swing brake  35  before the upperstructure  3  or the front work device  4  actually starts moving, the hydraulic control circuit  34  starts supplying the parking release hydraulic fluid to the cylinder  37  immediately before the hydraulic fluid starts being supplied to the actuators  3   a , and  4   d  to  4   f . That is, if the work levers  13  to  16  are operated, the swing brake  35  is released immediately before the upperstructure  3  or the front work device  4  starts operating. 
     Next, the configuration of the controller  50  is explained with reference to  FIG. 3 .  FIG. 3  is a block diagram illustrating the configuration of the controller  50  included in the hydraulic excavator  1 . The controller  50  acquires various types of signal output from the gate lock lever  17 , a temperature sensor  41 , a parking release pressure sensor  42 , and a travel pilot pressure sensor  43 , and controls the lock valve  31  and a notification device  44  on the basis of the acquired various types of signal. 
     For example, the temperature sensor  41  measures the temperature of the hydraulic fluid stored in the hydraulic fluid tank  32 , and outputs a temperature signal indicating the temperature acquired through the measurement to the controller  50 . The parking release pressure sensor  42  measures the pressure of the parking release hydraulic fluid supplied to the cylinder  37 , and outputs a pressure signal indicating the pressure acquired through the measurement to the controller  50 . The travel pilot pressure sensor  43  measures the pressures of the pilot hydraulic fluid output from the pilot valves  21  and  22 , and outputs pressure signals indicating the pressures acquired through the measurement to the controller  50 . 
     It is assumed that pressure sensors that detect pilot pressures in the present invention include pressure sensors that detect pilot pressures according to operation amounts of the boom lever  13 , the arm lever  14 , the bucket lever  15 , and the swing lever  16 , in addition to the parking release pressure sensor  42  and the travel pilot pressure sensor  43 . 
     The notification device  44  is a device that notifies various types of information to an operator who gets on the cab  7 . Although specific examples of the notification device  44  are not limited particularly, for example, the notification device  44  is a display that displays characters, images and videos, for example, a warning light, or a speaker that outputs sounds. 
     Although an illustration is omitted, the controller  50  includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). It should be noted, however, that the specific configuration of the controller  50  is not limited to this, and the controller  50  may be realized by hardware such as an ASIC (Application Specific Integrated Circuit) or a FPGA (Field-Programmable Gate Array). 
     By the CPU reading out program codes stored on the ROM, and executing them, the controller  50  functions as a switching section  51 , a decision-time correcting section  52 , a deciding section  53 , and a notification processing section  54  through cooperation between software and hardware. In addition, the RAM is used as a work area when the CPU executes the program. 
     The switching section  51  controls the switch position of the lock valve  31 . More specifically, in a case where the gate lock lever  17  is operated from the permission position for permitting an entrance of an operator into the operator&#39;s seat to the prohibition position for prohibiting an entrance of an operator into the operator&#39;s seat, the lock valve  31  is switched to the lock position for interrupting the supply of the pilot hydraulic fluid or to the release position for permitting the supply of the pilot hydraulic fluid on the basis of results from the deciding section  53  mentioned below, and also the lock valve  31  is switched to the release position or the lock position on the basis of results from the deciding section  53  mentioned below also in a case where the gate lock lever  17  is operated from the prohibition position to the permission position. 
     In addition, the switching section  51  switches the lock valve  31  from the release position to the lock position in response to a lapse of first time t 1  after the lock valve  31  is switched to the release position. Furthermore, after the lock valve  31  is switched to the lock position after the elapse of the first time t 1 , the switching section  51  switches the lock valve  31  again from the lock position to the release position in response to a notification from the deciding section  53  that there is no unintended operation. 
     On the basis of a temperature signal output from the temperature sensor  41 , the decision-time correcting section  52  corrects the value of the first time t 1 , and notifies the corrected first time t 1  to the switching section  51  and the deciding section  53 . The initial value of the first time t 1  is 0.2 seconds, for example. Then, the decision-time correcting section  52  increases the first time t 1  to be set, as the temperature of the hydraulic fluid indicated by the temperature signal lowers. This is because due to an increase of the viscosity of the hydraulic fluid that accompanies lowering of the temperature, the rising of the parking release pressure P 1 , and the travel pilot pressure P 2  mentioned below becomes slower. 
     The deciding section  53  decides whether or not the actuator operation devices  11  to  16  are operated until the first time t 1  elapses after the lock valve  31  is switched to the release position (operation at this timing is denoted “unintended operation”). In other words, the deciding section  53  decides whether or not the pilot hydraulic fluid is output from at least one of the pilot valves  21  to  26  until the first time t 1  elapses after the lock valve  31  is switched to the release position. Then, the deciding section  53  notifies results of the decision to the switching section  51  and the notification processing section  54 . 
     Note that typical examples of “unintended operation” in the present embodiment include operation of the gate lock lever  17  from the permission position to the prohibition position while the actuator operation devices  11  to  16  are being operated. For example, it can be assumed that an operator operates the gate lock lever  17  while the operator does not notice that his/her body hits the actuator operation devices  11  to  16  and the actuator operation device  11  to  16  are being operated. 
     As one example, the deciding section  53  decides that unintended operation has occurred in a case where the parking release pressure P 1  indicated by a pressure signal output from the parking release pressure sensor  42  becomes equal to or higher than a first threshold P th1  until the first time t 1  elapses after the lock valve  31  is switched to the release position. On the other hand, the deciding section  53  decides that unintended operation has not occurred in a case where the parking release pressure P 1  stayed lower than the first threshold P th1  until the first time t 1  elapses after the lock valve  31  is switched to the release position. Note that the first threshold P th1  is set to a value (e.g. 1 MPa) that is sufficiently lower than a parking release pressure P pk  (e.g. 4 MPa) necessary for releasing the swing brake  35 . 
     As another example, the deciding section  53  decides that unintended operation has occurred in a case where the travel pilot pressure P 2  indicated by a pressure signal output from the travel pilot pressure sensor  43  becomes equal to or higher than a second threshold P th2  until the first time t 1  elapses after the lock valve  31  is switched to the release position. On the other hand, the deciding section  53  decides that unintended operation has not occurred in a case where the travel pilot pressure P 2  stayed lower than the second threshold P th2  until the first time t 1  elapses after the lock valve  31  is switched to the release position. Note that the second threshold P th2  is set to a value (e.g. 0.6 MPa) that is sufficiently lower than a travel pilot pressure P tv  (e.g. up to 4 MPa) output from the pilot valves  21  and  22  at the time of operation of the travel levers  11  and  12 . 
     In response to a decision by the deciding section  53  that unintended operation has occurred, the notification processing section  54  gives, through the notification device  44 : a notification that unintended operation has occurred; a notification that the lock valve  31  is switched to the lock position in response to sensing of the occurrence of the unintended operation; a notification about how to switch the lock valve  31  from the lock position to the release position; or the like. That is, the notification processing section  54  may cause a display to display messages, turn on (flash) a warning light or cause a speaker to output sounds, for example. 
     Next, a process of the controller  50  is explained with reference to  FIG. 4  and  FIG. 5 .  FIG. 4  is a flowchart of an unintended-operation control process executed by the controller  50 .  FIG. 5  is a time chart illustrating temporal changes of the position of the gate lock lever  17 , the position of the lock valve  31 , whether or not the work levers  13  to  16  are operated, the parking release pressure, whether or not the travel levers  11  and  12  are operated, and the travel pilot pressure. Note that it is assumed that the gate lock lever  17  is at the permission position and the lock valve  31  is at the lock position at the time point of the start of the unintended-operation control process. 
     First, the switching section  51  monitors whether the gate lock lever  17  is operated from the permission position to the prohibition position (release operation) (S 11 ). In response to an output of a release signal from the gate lock lever  17  at time t 10  in  FIG. 5 , the switching section  51  determines that the gate lock lever  17  is operated from the permission position to the prohibition position. Then, in response to the operation of the gate lock lever  17  from the permission position to the prohibition position (S 11 : Yes), the switching section  51  switches the lock valve  31  from the lock position to the release position (S 12 ). 
     Next, on the basis of a temperature signal output from the temperature sensor  41 , the decision-time correcting section  52  corrects the first time t 1  (S 13 ). The specific method of correcting the first time t 1  is not particularly limited. For example, a table, a graph, a function or the like indicating the relationship between temperature and the first time t 1  is stored on the ROM, and the first time t 1  corresponding to the temperature indicated by the temperature signal may be acquired. Then, the decision-time correcting section  52  notifies the corrected first time t 1  to the switching section  51  and the deciding section  53 . 
     Next, until the first time t 1  elapses after the gate lock lever  17  is operated to the prohibition position (S 15 : No), the deciding section  53  monitors the values of the parking release pressure P 1  and the travel pilot pressure P 2  (S 14 ). More specifically, the deciding section  53  repetitively executes a process of acquiring the parking release pressure P 1  indicated by a pressure signal of the parking release pressure sensor  42 , and storing the acquired parking release pressure P 1  on the RAM. Similarly, the deciding section  53  repetitively executes a process of acquiring the travel pilot pressure P 2  indicated by a pressure signal of the travel pilot pressure sensor  43 , and storing the acquired travel pilot pressure P 2  on the RAM. 
     Next, in response to a lapse of the time t 1  after the gate lock lever  17  is operated to the prohibition position (time t 11  has come in  FIG. 5 ) (S 15 : Yes), the switching section  51  switches the lock valve  31  from the release position to the lock position (S 16 ). At this time, the gate lock lever  17  is kept at the prohibition position. That is, irrespective of the position of the gate lock lever  17 , the switching section  51  switches the lock valve  31  to the lock position at Step S 16 . 
     In addition, in response to a lapse of the time t 1  after the gate lock lever  17  is operated to the prohibition position (S 15 : Yes), the deciding section  53  compares the parking release pressure P 1  stored on the RAM with the first threshold P th1 , and compares the travel pilot pressure P 2  stored on the RAM with the second threshold P th2  (S 17 ). The first threshold P th1  and the second threshold P th2  are values predetermined through experiments, simulations or the like, for example, and are stored on the ROM. 
     Between time t 10  and time t 11  in  FIG. 5 , the parking release pressure P 1  and the travel pilot pressure P 2  stay at 0 MPa, and so the deciding section  53  decides that the parking release pressure P 1  is lower than the first threshold P th1 , and the travel pilot pressure P 2  is lower than the second threshold P th2  (S 17 : No). That is, the deciding section  53  decides that unintended operation has not occurred between time t 10  and time t 11 . Then, the deciding section  53  notifies the switching section  51  and the notification processing section  54  of results of the decision that unintended operation has not occurred. 
     Next, in response to the decision by the deciding section  53  that unintended operation has not occurred between time t 10  and time t 11  (S 17 : No), until second time t 2  elapses (S 18 : No), the switching section  51  waits without executing processes at and after Step S 19 . The second time t 2  is a predetermined length of time, for example, and is 0.2 seconds, for example. Note that the first time t 1  and the second time t 2  may have the same value or may have different values. 
     Then, in response to a lapse of the second time t 2  from time t 11  (time t 12  has come in  FIG. 5 ) (S 18 : Yes), the switching section  51  switches the lock valve  31  from the lock position to the release position (S 19 ). On the other hand, in a case where the deciding section  53  decides that unintended operation has not occurred between time t 10  and time t 11 , the notification processing section  54  may not execute any particular process. 
     Thereafter, if the work levers  13  to  16  are operated between time t 13  and time t 14 , the parking release pressure P 1  is detected, and the actuators  3   a  and  4   d  to  4   f  corresponding to the operated work levers  13  to  16  are driven. In addition, if the travel levers  11  and  12  are operated between time t 15  and time t 16 , the travel pilot pressure P 2  is detected, and the actuators  8   a  and  8   b  corresponding to the travel levers  11  and  12  are driven. 
     Next, if the operator operates the gate lock lever  17  from the prohibition position to the permission position at time t 20  in  FIG. 5 , the switching section  51  switches the lock valve  31  from the release position to the lock position. Then, the switching section  51  returns to Step S 11  again, and monitors whether the gate lock lever  17  is operated from the permission position to the prohibition position (S 11 ). 
     Next, even if the operator operates the work levers  13  to  16  at time t 21  in  FIG. 5 , the pilot hydraulic fluid is not output from the pilot valves  23  to  26  because the lock valve  31  is at the lock position, and also the parking release pressure P 1  is not detected at the parking release pressure sensor  42 . Note that it is assumed in this example that the state where the work levers  13  to  16  are operated continues from time t 21  to time t 24 . 
     Next, if the operator operates the gate lock lever  17  from the permission position to the prohibition position at time t 22  in  FIG. 5  (S 11 : Yes), the switching section  51  switches the lock valve  31  to the release position (S 12 ), the decision-time correcting section  52  corrects the first time t 1  (S 13 ), the deciding section  53  monitors the parking release pressure P 1  and the travel pilot pressure P 2  until the first time t 1  elapses (S 14 ), and, in response to a lapse of the first time t 1 , the switching section  51  switches the lock valve  31  to the lock position (S 15 ). 
     If the lock valve  31  is switched to the lock position at time t 23  in  FIG. 5 , the parking release pressure P 1  is no longer detected even if the work levers  13  to  16  remain being operated. Explanation of the processes of Steps S 12  to S 15  is similar to previously mentioned explanation, and so is not presented again. 
     If the gate lock lever  17  is operated to the prohibition position at time t 22  while the work levers  13  to  16  are being operated, the parking release pressure P 1  is detected by the parking release pressure sensor  42 . Accordingly, the deciding section  53  decides that the parking release pressure P 1  has become equal to or higher than the first threshold P th1  during the first time t 1  (between time t 22  and time t 23 ), and notifies the switching section  51  and the notification processing section  54  of results of the decision that unintended operation has occurred (S 17 : Yes). 
     Next, in response to the decision by the deciding section  53  that unintended operation has occurred between time t 22  and time t 23  (S 17 : Yes), the notification processing section  54  notifies the occurrence of the unintended operation through the notification device  44  (S 20 ). 
     On the other hand, in response to the decision by the deciding section  53  that unintended operation has occurred between time t 22  and time t 23  (S 17 : Yes), the switching section  51  does not execute the processes of Steps S 18  to S 19 , but monitors whether the gate lock lever  17  is operated from the prohibition position to the permission position (lock operation) (S 21 ). That is, the lock valve  31  is kept at the lock position. Then, even if the second time t 2  elapses from time t 23  or operation of the work levers  13  to  16  ends at time t 24 , the lock valve  31  is kept at the lock position. 
     Next, in response to operation of the gate lock lever  17  from the prohibition position to the permission position at time t 25  in  FIG. 5  (S 21 : Yes), the switching section  51  returns to Step S 11  again, and monitors whether the gate lock lever  17  is operated from the permission position to the prohibition position (S 11 ). It should be noted, however, that the lock valve  31  is already at the lock position, and so the switching section  51  does not need to switch the lock valve  31 . 
     Next, even if the operator operates the travel levers  11  and  12  at time t 31  in  FIG. 5 , the pilot hydraulic fluid is not output from the pilot valves  21  and  22  because the lock valve  31  is at the lock position, and also the travel pilot pressure P 2  is not detected at the travel pilot pressure sensor  43 . Note that it is assumed in this example that the state where the travel levers  11  and  12  are operated continues from time t 31  to time t 34 . 
     Next, if the operator operates the gate lock lever  17  from the permission position to the prohibition position at time t 32  in  FIG. 5  (S 11 : Yes), the switching section  51  switches the lock valve  31  to the release position (S 12 ), the decision-time correcting section  52  corrects the first time t 1  (S 13 ), the deciding section  53  monitors the parking release pressure P 1  and the travel pilot pressure P 2  until the first time t 1  elapses (S 14 ), and, in response to a lapse of the first time t 1 , the switching section  51  switches the lock valve  31  to the lock position (S 15 ). 
     If the lock valve  31  is switched to the lock position at time t 32  in  FIG. 5 , the travel pilot pressure P 2  is no longer detected even if the travel levers  11  and  12  remain being operated. Explanation of the processes of Steps S 12  to S 15  is similar to previously mentioned explanation, and so is not presented again. 
     If the gate lock lever  17  is operated to the prohibition position at time t 32  while the travel levers  11  and  12  are being operated, the travel pilot pressure P 2  is detected by the travel pilot pressure sensor  43 . Accordingly, the deciding section  53  decides that the travel pilot pressure P 2  has become equal to or higher than the second threshold P th2  during the first time t 1  (between time t 32  and time t 33 ), and notifies the switching section  51  and the notification processing section  54  of results of the decision that unintended operation has occurred (S 17 : Yes). 
     Note that if the gate lock lever  17  is operated to the prohibition position while the work levers  13  to  16  are being operated as illustrated in  FIG. 5 , the parking release pressure P 1  rises instantaneously to 6 MPa; on the contrary, if the gate lock lever  17  is operated to the prohibition position while the travel levers  11  and  12  are being operated, the travel pilot pressure P 2  rises slowly. Accordingly, the first time t 1  is desirably set longer than a length of time necessary for the travel pilot pressure P 2  to rise from 0 MPa to the second threshold P th2  (0.6 MPa). 
     Next, in response to the decision by the deciding section  53  that unintended operation has occurred between time t 32  and time t 33  (S 17 : Yes), the notification processing section  54  notifies the occurrence of the unintended operation through the notification device  44  (S 20 ). 
     On the other hand, in response to the decision by the deciding section  53  that unintended operation has occurred between time t 32  and time t 33  (S 17 : Yes), the switching section  51  does not execute the processes of Steps S 18  to S 19 , but monitors whether the gate lock lever  17  is operated from the prohibition position to the permission position (S 21 ). That is, the lock valve  31  is kept at the lock position. Then, even if the second time t 2  elapses from time t 33  or operation of the travel levers  11  and  12  ends at time t 34 , the lock valve  31  is kept at the lock position. 
     Next, in response to operation of the gate lock lever  17  from the prohibition position to the permission position at time t 35  in  FIG. 5  (S 21 : Yes), the switching section  51  returns to Step S 11  again, and monitors whether the gate lock lever  17  is operated from the permission position to the prohibition position (S 11 ). It should be noted, however, that the lock valve  31  is already at the lock position, and so the switching section  51  does not need to switch the lock valve  31 . Explanation of the subsequent processes is similar to previously mentioned explanation, and so is not presented again. 
     The embodiment described above provides the following action and effects, for example. 
     In the embodiment described above, if the gate lock lever  17  is operated to the prohibition position, the lock valve  31  is switched to the release position only for the first time t 1 , and whether or not unintended operation has occurred is decided until the first time t 1  elapses. Then, if unintended operation has not occurred, the lock valve  31  is switched to the release position, and if unintended operation has occurred, the lock valve  31  is kept at the lock position. Thereby, as compared with a case where whether or not unintended operation has occurred is decided with the lock valve  31  being kept at the release position, and the lock valve  31  is switched to the lock position if it is decided that unintended operation has occurred, it is possible to stop unexpected operation of the actuators  3   a ,  4   d  to  4   f , and  8   a  to  8   b  faster. 
     In addition, as the temperature lowers, the viscosity of the hydraulic fluid becomes higher, and so the rising of the travel pilot pressure P 2  in particular becomes slower. In view of this, by making longer the time (first time) t 1  for a decision about the travel pilot pressure P 2  at Steps S 14  to S 15  as the temperature of the hydraulic fluid lowers as in the embodiment described above, it is possible to decide fast whether or not unintended operation has occurred. 
     In addition, according to the embodiment described above, whether or not unintended operation of the work levers  13  to  16  has occurred is decided on the basis of the parking release pressure P 1 . The parking release pressure P 1  rises no matter which of the work levers  13  to  16  is operated. Accordingly, by detecting the parking release pressure P 1  at the parking release pressure sensor  42 , the number of sensors can be reduced as compared with a case where a sensor is provided for each of the pilot valves  23  to  26 . In addition, the rising of a detection signal of the parking release pressure P 1  is faster (the parking release pressure P 1  rises instantaneously) as compared with the rising of a detection signal of the pilot pressure due to operation of the work levers  13  to  16 , and so whether or not unintended operation of the work lever  13  to  16  has occurred can be decided more promptly and surely. As a result, for example, it is possible to prevent more surely the upperstructure  3  from rotating due to inertia. 
     In addition, according to the embodiment described above, an occurrence of unintended operation is notified through the notification device  44  (S 20 ). Furthermore, according to the embodiment described above, in a case where it is decided that unintended operation has occurred, in order to switch the lock valve  31  to the release position again, the operator needs to operate the gate lock lever  17  to the permission position once (S 21 : Yes), and to the prohibition position again (S 11 : Yes). By causing the operator to execute such a procedure, it is possible to make the operator aware of the occurrence of the unintended operation. As a result, it is possible to expect that the gate lock lever  17  is operated to the prohibition position after the unintended operation is dealt with. 
     The embodiment mentioned above is illustrated for the purpose of explaining the present invention, and it is not intended to limit the scope of the present invention only to the embodiment. Those skilled in the art can implement the present invention in various other aspects without deviating from the gist of the present invention. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  . . . hydraulic excavator, 
               2  . . . undercarriage, 
               3  . . . upperstructure, 
               3   a  . . . swing motor, 
               4  . . . front work device, 
               4   a  . . . boom, 
               4   b  . . . arm, 
               4   c  . . . bucket, 
               4   d  . . . boom cylinder, 
               4   e  . . . arm cylinder, 
               4   f  . . . bucket cylinder, 
               5  . . . swing frame, 
               6  . . . counter weight, 
               7  . . . cab, 
               8  . . . crawler, 
               8   a ,  8   b  . . . hydraulic motor, 
               8   c  . . . driving wheel, 
               10  . . . engine, 
               11 ,  12  . . . travel lever (travel operation device), 
               13  . . . boom lever, 
               14  . . . arm lever, 
               15  . . . bucket lever, 
               16  . . . swing lever, 
               17  . . . gate lock lever (lock operation device), 
               21 ,  22 ,  23 ,  24 ,  25 ,  26  . . . pilot valve, 
               31  . . . lock valve, 
               32  . . . hydraulic fluid tank, 
               33  . . . hydraulic pump, 
               34  . . . hydraulic control circuit, 
               35  . . . swing brake, 
               36  . . . brake pad, 
               37  . . . cylinder, 
               38  . . . coil spring, 
               41  . . . temperature sensor, 
               42  . . . parking release pressure sensor, 
               43  . . . travel pilot pressure sensor, 
               44  . . . notification device, 
               50  . . . controller, 
               51  . . . switching section, 
               52  . . . decision-time correcting section, 
               53  . . . deciding section, 
               54  . . . notification processing section