Patent Publication Number: US-2021171134-A1

Title: Crawler traveling apparatus, crawler monitoring system, crawler traveling vehicle and crawler monitoring method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a crawler traveling apparatus, a crawler monitoring system, a crawler traveling vehicle and a crawler monitoring method. 
     BACKGROUND 
     Conventionally, a work vehicle including a machine body which is supported by a crawler traveling apparatus having an endless rubber crawler such that the machine body is self-propelled has been known. US20170242446A1 (PTL 1) and US20170242447A1 (PTL 2) disclose this kind of work vehicle. 
     In the work vehicle disclosed in PTL 1 and PTL 2, a support beam which supports an idler wheel of the crawler traveling apparatus is supported by the machine body by a pivot pin. In the work vehicle disclosed in PTL 1, a load applied to the pivot pin is monitored, and a speed of the word vehicle is controlled. In the work vehicle disclosed in PTL 2, an axle load is evaluated from a load applied to the pivot pin, and an operation of the work vehicle is controlled based on the evaluated axle load. 
     CITATION LIST 
     Patent Literature 
     PTL 1: US20170242446A1 
     PTL 2: US20170242447A1 
     SUMMARY 
     In the work vehicle including the rubber crawler as disclosed in PTL 1 and PTL 2, for example, in a sudden cornering situation or during an operation on an inclined surface, a tension wheel as an idler wheel may be disengaged from the rubber crawler. The work vehicle as a crawler traveling vehicle disclosed in PTL 1 and PTL 2 cannot detect disengagement of the tension wheel from the rubber crawler. Occurrence of wheel-disengagement causes downtime, which causes work delay. Consequently, to prevent the wheel-disengagement previously, an operator of the crawler traveling vehicle is required to grasp a sign of the wheel-disengagement sensuously from an attitude of the machine body, a traveling state, a sound etc. to take measures against wheel-disengagement. However, sensuously grasping the sign of the wheel-disengagement is not easy for the operator. 
     An object of the present disclosure is to provide a crawler traveling apparatus, a crawler monitoring system, a crawler traveling vehicle and a crawler monitoring method which can detect a sign that the tension wheel is disengaged from the rubber crawler. 
     According to a first aspect of the present disclosure, there is provided a crawler traveling apparatus including: an endless rubber crawler; a drive wheel which drives to rotate the rubber crawler in a crawler circumferential direction; a tension wheel which stretches the rubber crawler together with the drive wheel to be rotated accompanied by rotation of the rubber crawler; and a sensor which can acquire load information related to a load that the tension wheel receives from the rubber crawler, wherein the rubber crawler includes an endless crawler belt and a plurality of cores which are arranged along the crawler circumferential direction of the crawler belt with an interval and embedded in the crawler belt, each core includes a pair of core projections which project from an inner surface of the crawler belt to an inner side and are arranged in a crawler width direction with an interval, the tension wheel abuts an inner surface of the rubber crawler at least, in the crawler width direction, at any of a position between the pair of core projections and both outer positions of the pair of core projections to be rotated following the rubber crawler, the sensor can acquire tension load information in a crawler thickness direction that the tension wheel receives from the inner surface of the rubber crawler as the load information. 
     According to a second aspect of the present disclosure, there is provided a crawler monitoring system including the above-described crawler traveling apparatus and a control device which compares the tension load information acquired by the sensor with a predetermined threshold value to execute processing in accordance with a comparison result. 
     According to a third aspect of the present disclosure, there is provided a crawler traveling vehicle including: a machine body; and a crawler traveling apparatus which supports the machine body such that the machine body is self-propelled, the crawler traveling apparatus includes: an endless rubber crawler; a drive wheel which drives to rotate the rubber crawler in a crawler circumferential direction; a tension wheel which stretches the rubber crawler together with the drive wheel to be rotated accompanied by rotation of the rubber crawler; and a sensor which can acquire load information related to a load that the tension wheel receives from the rubber crawler, wherein the machine body includes a control device which compares the load information acquired by the sensor with a predetermined threshold value to execute processing in accordance with a comparison result, the rubber crawler includes: an endless crawler belt; and a plurality of cores which are arranged along the crawler circumferential direction of the crawler belt with an interval and embedded in the crawler belt, wherein each core includes a pair of core projections which protrude from an inner surface of the crawler belt to an inner side and are arranged in a crawler width direction with an interval, the tension wheel abuts an inner surface of the rubber crawler at least, in the crawler width direction, at any of a position between the pair of core projections and both outer positions of the pair of core projections to be rotated following the rubber crawler, the sensor can acquire tension load information in a crawler thickness direction that the tension wheel receives from the inner surface of the rubber crawler as the load information, the control device compares the tension load information acquired by the sensor with a predetermined threshold value to execute processing in accordance with a comparison result. 
     According to a fourth aspect of the present disclosure, there is provided a crawler monitoring method of monitoring disengagement of a tension wheel from an endless rubber crawler based on load information related to a load that the tension wheel receives from the rubber crawler stretched by a drive wheel and the tension wheel, wherein the rubber crawler includes an endless crawler belt and a plurality of cores which are arranged along a crawler circumferential direction of the crawler belt with an interval and embedded in the crawler belt, each core includes a pair of core projections which project from an inner surface of the crawler belt to an inner side and are arranged in a crawler width direction with an interval, the tension wheel abuts an inner surface of the rubber crawler at least, in the crawler width direction, at any of a position between the pair of core projections and both outer positions of the pair of core projections to be rotated following the rubber crawler, disengagement of the tension wheel from the rubber crawler is monitored based on, of the load information, tension load information in a crawler thickness direction that the tension wheel receives from the inner surface of the rubber crawler. 
     According to the present disclosure, the crawler traveling apparatus, the crawler monitoring system, the crawler traveling vehicle and the crawler monitoring method which can detect the sign that the tension wheel is disengaged from the rubber crawler can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a side view of a crawler traveling vehicle as one embodiment of the present disclosure; 
         FIG. 2  is an enlarged view of the crawler traveling apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a drawing illustrating a detail of a rubber crawler illustrated in  FIG. 1 ; 
         FIG. 4  is a drawing illustrating a biasing body of the crawler traveling apparatus illustrated in  FIG. 2 ; 
         FIG. 5A  to  FIG. 5D  are schematic diagrams illustrating an outline of a series of operations in which the tension wheel illustrated in  FIG. 1  is disengaged from the rubber crawler; 
         FIG. 6  is a drawing illustrating the biasing body of the crawler traveling apparatus illustrated in  FIG. 2 , illustrating a state that a forward traveling side tension wheel illustrated in  FIG. 2  completely overrides a projection of a core; and 
         FIG. 7  is an image diagram illustrating an example of change of a load that the forward traveling side tension wheel receives from an inner surface of the rubber crawler from a state illustrated in  FIG. 5A  to a state illustrated in  FIG. 5D . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment of a crawler traveling apparatus, a crawler monitoring system, a crawler traveling vehicle and a crawler monitoring method according to the present disclosure will be explained with illustration with reference to the drawings. In each drawing, common members and portions are applied the same reference numerals. 
       FIG. 1  is a side view of a crawler traveling vehicle  1  as one embodiment of the present disclosure. As illustrated in  FIG. 1 , the crawler traveling vehicle  1  includes a machine body  2  and a crawler traveling apparatus  3  as one embodiment of the present disclosure. The crawler traveling apparatus  3  supports the machine body  2  such that the machine body  2  is self-propelled. The crawler traveling vehicle  1  includes a pair of crawler traveling apparatuses  3 . The pair of crawler traveling apparatuses  3  are attached to the machine body  2  rotatably to the machine body  2  at both sides in a width direction of the machine body  2 . 
     The crawler traveling vehicle  1  of this embodiment illustrated in  FIG. 1  is a compact track loader. However, the crawler traveling vehicle according to the present disclosure is not limited to a compact track loader, and may be a crawler traveling vehicle for other works. 
     The machine body  2  of this embodiment includes a machine main body  11 , a machine body arm  12  and a hydraulic cylinder  13 . The machine body arm  12  is attached to be vertically movable to the machine main body  11 . The vertical movement of the machine body arm  12  to the machine main body  11  is executed by expansion and contraction of the hydraulic cylinder  13 . To the machine main body  11 , an operator&#39;s cab  11   a  which an operator can get in is provided. The vertical movement of the above-described machine body arm  12  can be controlled through an operation of an operating device  22  provided to the operator&#39;s cab  11   a . While a bucket  14  is attached at a tip portion of the machine body arm  12  illustrated in  FIG. 1 , this is not limited to the bucket  14 . To the tip portion of the machine body arm  12 , an attachment in accordance with a work can be attached, including a bucket having a different shape from that of the bucket  14  illustrated in  FIG. 1 , various forks, and others. 
     Also, the machine body  2  includes a control device  21 , the operating device  22 , a drive device  23 , a notification device  24  and a pressure adjusting device  25 . 
     The control device  21  includes a processing section constituted by a processor, for example, a CPU (Central Processing Unit) and an MPU (Micro-Processing Unit). The control device  21  includes a storage section constituted by a memory, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory). The storage section stores a program etc. for operating the operating device  22 , the drive device  23 , the notification device  24 , the pressure adjusting device  25 , etc. The processing section executes the program stored in the storage section to activate the operating device  22 , the drive device  23 , the notification device  24 , the pressure adjusting device  25 , etc. The machine body  2  may include a storage device which is different from the control device  21  in addition to or instead of the storage section of the control device  21 . 
     The operating device  22  includes an operating section constituted by a touch panel, a button switch, a keyboard, etc. and an input section for inputting operation information based on the operation by the operating section to the control device  21 . The configuration of the operating device  22  is not particularly limited, and any configuration may be applied as long as the operation information based on the operation by the operator can be inputted into the control device  21 . 
     The drive device  23  can drive the crawler traveling apparatus  3 . The drive device  23  includes a power source such as an engine. The crawler traveling apparatus  3  is driven by a driving force from the power source. The driving of the crawler traveling apparatus  3  by the drive device  23  is controlled by the control device  21 . Also, the drive device  23  can drive the hydraulic cylinder  13 . The control device  21  can control the vertical movement of the machine body arm  12  to the machine main body  11  by controlling the drive of the hydraulic cylinder  13  by the drive device  23 . 
     The notification device  24  includes a notification section constituted by a liquid crystal panel, a speaker, etc. The control device  21  controls the notification device  24  based on acquisition information acquired by a sensor  34  of the crawler traveling apparatus  3  which will be described later. More specifically, the control device  21  can notify the operator in the operator&#39;s cab  11   a  of notification information in accordance with the acquisition information acquired by the sensor  34  through the notification section of the notification device  24 . The notification information may be any information as long as it is information which can be perceived through visual perception, auditory perception, etc., and is not particularly limited. The notification information may be display information such as a symbol, a letter and a color to be displayed on a display including a liquid crystal panel, or may be sound information emitted from a sound emitting section including a speaker. A touch panel used as the notification section may be also used as the operation section of the operating device  22 . 
     Also, the control device  21 , the operating device  22  and the notification device  24  may be constituted by one computer including these components. The computer including the control device  21 , the operating device  22  and the notification device  24  may further include other devices including a communication device and a storage device. 
     The pressure adjusting device  25  can adjust an internal pressure of a fluid element  51  in a biasing body  50  of the crawler traveling apparatus  3  while will be described later, and adjust a pressing force to a rubber crawler  33  by a tension wheel  35  which will be described later. The pressure adjusting device  25  includes, for example, a power source such as a hydraulic pump. The adjustment of the internal pressure of the fluid element  51  by the pressure adjusting device  25  is controlled by the control device  21 , for example. 
       FIG. 2  is an enlarged view in which the crawler traveling apparatus  3  illustrated in  FIG. 1  is enlarged and illustrated. As illustrated in  FIGS. 1 and 2 , the crawler traveling apparatus  3  includes a drive wheel  31 , an idler wheel  32 , the endless rubber crawler  33 , the sensor  34  and the biasing body  50 .  FIG. 3  is a cross-section perspective view illustrating the detail of the rubber crawler  33 . 
     The drive wheel  31  and the idler wheel  32  are attached rotatably to the machine body  2 . The drive wheel  31  and the idler wheel  32  may be directly or indirectly attached rotatably to the machine body  2 . The drive wheel  31  and the idler wheel  32  may be attached rotatably to a rotating shaft of the machine body  2 , or may be attached rotatably to a rotating shaft provided to another member fixed to the machine body  2 . The drive wheel  31  of this embodiment is attached rotatably to a rotating shaft  72  of the machine main body  11  of the machine body  2 . The idler wheel  32  of this embodiment is attached rotatably to a shaft portion  71  attached to a frame member  70  fixed to the machine main body  11  of the machine body  2 . The drive wheel  31  is driven to rotate to a forward traveling side or a backward traveling side by the drive device  23  of the machine body  2 . The rotational drive of the drive wheel  31  by the drive device  23  is controlled by the control device  21 . The rubber crawler  33  is driven to rotate in a crawler circumferential direction A by the drive wheel  31 . The idler wheel  32  is rotated following the rubber crawler  33  which is driven to rotate by the rotation of the drive wheel  31 . 
     The drive wheel  31  of this embodiment is a sprocket. Consequently, the drive wheel  31  of this embodiment includes a plurality of projections  31   a  arranged with a predetermined pitch over the entire area in a circumferential direction to protrude toward a radially outer side. The drive wheel  31  drives the rubber crawler  33  to rotate in the crawler circumferential direction A since the plurality of projections  31   a  rotate while they are sequentially fitted to a plurality of recesses  37   a  provided at an inner surface of the rubber crawler  33  arranged in the crawler circumferential direction A. 
     The idler wheel  32  abuts the inner surface of the rubber crawler  33  and is rotated following the rubber crawler  33 . The idler wheel  32  may abut the inner surface of the rubber crawler  33 , in a crawler width direction C, at any of a position between a pair of core projections  41  of a core  38  of the rubber crawler  33  which will be explained later. The idler wheel  32  may abut the inner surface of the rubber crawler  33 , in a crawler width direction C, at both outer positions of the pair of core projections  41 . The idler wheel  32  may abut the inner surface of the rubber crawler  33  both at the above position between a pair of core projections  41  and at the above outer positions of the pair of core projections  41 . 
     The crawler traveling apparatus  3  of this embodiment includes both the tension wheel  35  as the idler wheel  32  and a track roller  36  as the idler wheel  32 . As illustrated in  FIGS. 1 and 2 , the tension wheel  35  and the track roller  36  of this embodiment rotate about the shaft portion  71  attached to the frame member  70  fixed to the machine body  2 . 
     The tension wheel  35  stretches the rubber crawler  33  together with the drive wheel  31 . Also, the tension wheel  35  is rotated accompanied by the rotation of the rubber crawler  33 . More specifically, the tension wheel  35  of this embodiment abuts an inner surface  40   c  of a core body  40  which will be explained later at the position between the pair of core projections  41  which will be explained later in the crawler width direction C and is rotated following the rubber crawler  33 . The inner surface  40   c  of the core body  40  constitutes a part of the inner surface of the rubber crawler  33 . However, the tension wheel  35  may be configured to abut the inner surface of the rubber crawler  33  at the both outer positions of the pair of core projections  41  which will be explained later in the crawler width direction C to be rotated following the rubber crawler  33 . 
     While the crawler traveling apparatus  3  of this embodiment includes two tension wheels  35 , the number of tension wheels  35  is not limited to two. One tension wheel  35  or three or more tension wheels  35  may be applied. 
     The two tension wheels  35  of this embodiment are constituted by a forward traveling side tension wheel  35   a  used as a front idler wheel and a backward traveling side tension wheel  35   b  used as a rear idler wheel. The forward traveling side tension wheel  35   a  and the backward traveling side tension wheel  35   b  contact the inner surface of the rubber crawler  33 . Also, the forward traveling side tension wheel  35   a  and the backward traveling side tension wheel  35   b  contact a contact patch via the rubber crawler  33 . The rubber crawler  33  of this embodiment is applied a tension by the forward traveling side tension wheel  35   a , the backward traveling side tension wheel  35   b  and the drive wheel  31 . The drive wheel  31  is positioned at an upper side in a vertical direction from the forward traveling side tension wheel  35   a  and the backward traveling side tension wheel  35   b . Due to this, the rubber crawler  33  of this embodiment has a substantially triangular outer shape in a side view (see  FIG. 2  etc.) However, for example, the rubber crawler  33  may be stretched by the drive wheel  31  disposed at one side of the forward traveling side and the backward traveling side and one tension wheel  35  disposed at the other side of the forward traveling side and the backward traveling side. In this case, the rubber crawler  33  has an oval outer shape which is elongated in a front-rear direction B in which a portion stretched between the drive wheel  31  and the tension wheel  35  linearly extends in the front-rear direction B in the side view. 
     The forward traveling side tension wheel  35   a  of this embodiment is biased toward the inner surface of the rubber crawler  33  by the biasing body  50  which will be explained later. In other words, the tension of the rubber crawler  33  can be adjusted by changing a biasing force to the forward traveling side tension wheel  35   a  by the biasing body  50 . The details of the biasing body  50  of this embodiment will be explained later (see  FIGS. 5 and 6 ). 
     The track roller  36  abuts the inner surface of the rubber crawler  33  to which the tension is applied by the drive wheel  31  and the tension wheel  35  to be rotated following the rubber crawler  33 . More specifically, the track roller  36  of this embodiment abuts an inner surface  37   c  of a crawler belt  37  which will be explained later at the both outer positions of the pair of core projections  41  which will be explained later in the crawler width direction C and is rotated following the rubber crawler  33 . The inner surface  37   c  of the crawler belt  37  constitutes a part of the inner surface of the rubber crawler  33 . However, the track roller  36  may be configured to abut the inner surface of the rubber crawler  33  at the position between the pair of core projections  41  which will be explained later in the crawler width direction C to be rotated following the rubber crawler  33 . 
     While the crawler traveling apparatus  3  of this embodiment includes three track rollers  36 , the number of the track rollers  36  is not limited to three. Less than three, or four or more track rollers  36  may be applied. 
     The three track rollers  36  of this embodiment are constituted by a forward traveling side track roller  36   a , an intermediate track roller  36   b  and a backward traveling side track roller  36   c . The three track rollers  36  of this embodiment contact the contact patch via the rubber crawler  33 . In other words, the three track rollers  36  of this embodiment contact an inner surface of a ground contact region  33   a  of the rubber crawler  33 , which is stretched between the forward traveling side tension wheel  35   a  and a backward traveling side tension wheel  35   b , with an outer circumferential surface of the ground contact region  33   a  contacting the contact patch. The forward traveling side track roller  36   a  is arranged at a position which is closest to the forward traveling side tension wheel  35   a  in the inner surface of the ground contact region  33   a  of the rubber crawler  33 . The backward traveling side track roller  36   c  is arranged at a position which is closest to the backward traveling side tension wheel  35   b  in the inner surface of the ground contact region  33   a  of the rubber crawler  33 . The intermediate track roller  36   b  is arranged between the forward traveling side track roller  36   a  and the backward traveling side track roller  36   c  in the front-rear direction B. While the crawler traveling apparatus  3  of this embodiment includes only one intermediate track roller  36   b , a configuration of including two or more intermediate track rollers  36   b  may be applied. Also, the crawler traveling apparatus  3  may include another track roller  36  which abuts, of the rubber crawler  33 , an inner surface of a portion stretched between the drive wheel  31  and the forward traveling side tension wheel  35   a  or an inner surface of a portion stretched between the drive wheel  31  and the backward traveling side tension wheel  35   b.    
     The endless rubber crawler  33  is wound around the drive wheel  31  and the idler wheel  32 . 
     As illustrated in  FIG. 3 , the rubber crawler  33  includes the endless crawler belt  37 , a plurality of cores  38  and a reinforcement cord layer  39 . 
     An outer circumferential surface of the crawler belt  37  is a surface which contacts the contact patch and in which lugs  37   b  projecting toward an outer side are formed over the entire area in the crawler circumferential direction A with intervals. An inner circumferential surface of the crawler belt  37  is formed with the plurality of recesses  37   a  to which the projections  31   a  of the drive wheel  31  are fitted. More specifically, each recess  37   a  is formed between the cores  38  which are adjacent in the crawler circumferential direction A at the position between the pair of core projections  41  which will be explained later in the crawler width direction C. 
     As illustrated in  FIG. 3 , the plurality of cores  38  are arranged along the crawler circumferential direction A of the crawler belt  37  with intervals. Also, the plurality of cores  38  are embedded in the crawler belt  37 . 
     More specifically, the core  38  includes the plate-like core body  40  embedded in the crawler belt  37  to extend in the crawler width direction C and the pair of core projections  41  projecting from the core body  40 . The plate-like core body  40  is embedded in the crawler belt  37  such that its thickness direction substantially corresponds to a crawler thickness direction D. The pair of core projections  41  project toward an inner side of the rubber crawler  33  than the crawler belt  37 . Also, the pair of core projections  41  are arranged with an interval in the crawler width direction C. Further, the pair of core projections  41  are arranged to face each other in the crawler width direction C. Of the core body  40 , an inner surface  40   c  of a portion between the pair of core projections  41  in the crawler width direction C is exposed to the inner side of the rubber crawler  33  to constitute a part of the inner surface of the rubber crawler  33 . 
     The reinforcement cord layer  39  is constituted by a plurality of steel cords embedded in the crawler belt  37  and arranged in parallel. The reinforcement cord layer  39  is embedded at an outer circumferential surface side of the crawler belt  37  than the core body  40 . While the rubber crawler  33  of this embodiment is configured to include the reinforcement cord layer  39 , not limited to this configuration, a rubber crawler not including the reinforcement cord layer  39  may be applied. 
     The sensor  34  can acquire load information related to a load that the tension wheel  35  receives from the rubber crawler  33 . The load information may be various information correlated with the load, not limited to the load itself. More specifically, the sensor  34  can acquire load information in the crawler thickness direction D (hereinafter, it is referred to as “tension load information”) that the tension wheel  35  receives from the inner surface of the rubber crawler  33  as the load information. The tension load information may be, for example, an electric signal correlated with the load. Use of the tension load information acquired by the sensor  34  can inhibit disengagement of the tension wheel  35  from the rubber crawler  33 . The details will be explained later (see  FIG. 7  etc.) 
     As illustrated in  FIGS. 1 and 2 , in this embodiment, the forward traveling side tension wheel  35   a  is the tension wheel  35  on which the tension load information is acquired by the sensor  34 . However, the backward traveling side tension wheel  35   b  may be applied. 
     The sensor  34  is not particularly limited as long as it is a sensor which can directly or indirectly acquire the tension load information such as a load sensor and a pressure sensor. Although the detail will be described later, the sensor  34  of this embodiment is a pressure sensor which can acquire the pressure of the fluid element  51  of the biasing body  50  which will be described later as the tension load information. The pressure sensor as the sensor  34  is attached to a connecting section  52   b  of a cylinder  52  which will be explained later. The details will be explained later. 
       FIG. 4  is a drawing illustrating the biasing body  50  of this embodiment. As illustrated in  FIG. 4 , the biasing body  50  biases the tension wheel  35  toward the inner surface of the rubber crawler  33 . The biasing body  50  of this embodiment biases the forward traveling side tension wheel  35   a  of the two tension wheels  35  toward the inner surface of the rubber crawler  33 . The sensor  34  of this embodiment acquires biasing load information that the biasing body  50  receives from the tension wheel  35  as the tension load information. Since the biasing body  50  biases the forward traveling side tension wheel  35   a  in this embodiment, the sensor  34  of this embodiment acquires the biasing load information that the biasing body  50  receives from the forward traveling side tension wheel  35   a  as the tension load information. However, the biasing body  50  may bias the backward traveling side tension wheel  35   b . In this case, the sensor  34  may acquire the biasing load information that the biasing body  50  receives from the backward traveling side tension wheel  35   b  as the tension load information. 
     More specifically, the biasing body  50  of this embodiment includes the fluid element  51 , the cylinder  52  and a piston rod  53 . The cylinder  52  defines an accommodation space  52   a  in its inner portion to house the fluid element  51  in the accommodation space  52   a . While gas including air or semifluid including grease may be used for example, the fluid element  51  is not particularly limited as long as it is a fluid element capable of compressive deformation. Also, an end of the cylinder  52  in an axial direction E is open, and the piston rod  53  enters the accommodation space  52   a  from the end of the cylinder  52 . The piston rod  53  can compress the fluid element  51  housed in the accommodation space  52   a  by moving in the axial direction E of the cylinder  52 . 
     Here, a connecting section  52   b  which can be connected to the pressure adjusting device  25  of the machine body  2  is provided to the cylinder  52  of the biasing body  50 . The sensor  34  of this embodiment is attached to the connecting section  52   b . By doing this, the sensor  34  can acquire the internal pressure of the fluid element  51  in the accommodation space  52   a  of the cylinder  52  as the biasing load information. Since the attachment of the sensor  34  is executed using the connecting section  52   b  for the pressure adjusting device  25 , the sensor  34  can be easily provided. The pressure adjusting device  25  of this embodiment is connected to the biasing body  50  via the sensor  34 . More specifically, the pressure adjusting device  25  of this embodiment is connected to the connecting section  52   b  of the cylinder  52  of the biasing body  50  via the sensor  34 . In other words, the sensor  34  of this embodiment includes a first connecting section  34   a  which can be connected to the connecting section  52   b  of the cylinder  52  of the biasing body  50  and a second connecting section  34   b  which can be connected to the pressure adjusting device  25 . The configuration of the connecting section  52   b  of the biasing body  50  to which the sensor  34  and the pressure adjusting device  25  are attached is not particularly limited. The connecting section  52   b  can be configured by a connecting nipple to which the sensor  34  and the pressure adjusting device  25  are attached, for example. 
     While the machine body  2  includes the pressure adjusting device  25  in this embodiment, the machine body not including the pressure adjusting device  25  may be applied. For example, the pressure adjusting device  25  may be configured as an external device separated from the crawler traveling vehicle  1  to be used with connection to the connecting section  52   b  in accordance with need. In this case, when adjustment of the internal pressure of the fluid element  51  of the biasing body  50  is required, instead of the sensor  34  connected to the connecting section  52   b  of the cylinder  52 , the pressure adjusting device  25  may be connected. In other words, while the pressure adjusting device  25  is connected to the biasing body  50  via the sensor  34  in the crawler traveling vehicle  1  of this embodiment, the configuration is not limited to this. Such a configuration may be applied that the sensor  34  and the pressure adjusting device  25  can be alternatively attached to the connecting section  52   b  of the biasing body  50 . However, with the configuration that the pressure adjusting device  25  is connected to the biasing body  50  via the sensor  34  as in this embodiment, the pressure adjusting device  25  can be connected to the biasing body  50  without the need of removing the sensor  34 . In this case, the tension load information can be acquired by the sensor  34  in a state that adjustment of the internal pressure of the fluid element  51  by the pressure adjusting device  25  is remained as possible. 
     A reaction force when the biasing body  50  biases the tension wheel  35  may be secured by various regions fixed to the machine body  2  such as the frame member  70  fixed to the machine body  2 . 
     Hereinafter, control such that disengagement of the tension wheel  35  from the rubber crawler  33  is previously prevented based on the tension load information acquired by the sensor  34  will be explained in detail. Here, “disengagement of the tension wheel  35  from the rubber crawler  33 ” means a state that the tension wheel  35  overrides the core projection  41  of the core  38  of the rubber crawler  33  in the crawler width direction C. 
       FIGS. 5A to 5D  are schematic diagrams illustrating an outline of a series of operations in which the tension wheel  35  of this embodiment is disengaged from the rubber crawler  33 . The tension wheel  35  illustrated in  FIGS. 5A to 5D  is the forward traveling side tension wheel  35   a .  FIG. 5A  is a drawing illustrating a position of the forward traveling side tension wheel  35   a  at a normal time when the forward traveling side tension wheel  35   a  is not disengaged from the rubber crawler  33 . As illustrated in  FIG. 5A , the forward traveling side tension wheel  35   a  of this embodiment rotates about the shaft portion  71  at the position between the pair of core projections  41  in the crawler width direction C at the normal time when the forward traveling side tension wheel  35   a  is not disengaged from the rubber crawler  33 . 
       FIG. 5B  is a drawing illustrating a state that, from a state illustrated in  FIG. 5A , the forward traveling side tension wheel  35   a  is relatively moved to one side in the crawler width direction C to the rubber crawler  33  and the forward traveling side tension wheel  35   a  abuts a side surface of the core projection  41 .  FIG. 5C  is a drawing illustrating a state that, from the state illustrated in  FIG. 5B , the forward traveling side tension wheel  35   a  is further relatively moved to the one side in the crawler width direction C to the rubber crawler  33  and the forward traveling side tension wheel  35   a  is in the middle of overriding the side surface of the core projection  41 .  FIG. 5D  is a drawing illustrating a state that, from the state illustrated in  FIG. 5C , the forward traveling side tension wheel  35   a  is further relatively moved to the one side in the crawler width direction C to the rubber crawler  33  and the forward traveling side tension wheel  35   a  completely overrides the core projection  41 . 
       FIG. 6  is a drawing illustrating the biasing body  50  of this embodiment in the same manner as  FIG. 4 . Additionally, while the forward traveling side tension wheel  35   a  illustrated in  FIG. 4  is in a state of the normal time as illustrated in  FIG. 5A , the forward traveling side tension wheel  35   a  illustrated in  FIG. 6  is in a state of completely overriding the core projection  41  as illustrated in  FIG. 5D . In  FIGS. 4 and 6 , for convenience of explanation, the forward traveling side tension wheel  35   a  and the rubber crawler  33  are partially simplified. 
     As illustrated in  FIG. 6 , when the forward traveling side tension wheel  35   a  overrides the core projection  41 , by the amount of overriding, a biasing force that the forward traveling side tension wheel  35   a  biases the rubber crawler  33  is made larger (see an upward thick arrow in  FIG. 6 ). Consequently, the tension of the rubber crawler  33  is made higher, which increases a tension load that the forward traveling side tension wheel  35   a  receives from the inner surface of the rubber crawler  33  in the crawler thickness direction D, especially, in the crawler thickness direction D along the front-rear direction B (see a right thick arrow in  FIG. 6 ). Due to this, in this embodiment, a biasing load that the biasing body  50  receives from the forward traveling side tension wheel  35   a  is made larger. As a result, the internal pressure of the fluid element  51  in the cylinder  52  of the biasing body  50  of this embodiment is also fluctuated. 
       FIG. 7  is an image diagram illustrating an example of change of a load that the forward traveling side tension wheel  35   a  receives from the inner surface of the rubber crawler  33  from the state illustrated in  FIG. 5A  to the state illustrated in  FIG. 5D . An abscissa of the drawing illustrated in  FIG. 7  refers to a relative position of the forward traveling side tension wheel  35   a  and the rubber crawler  33  in the crawler width direction C. The abscissa of the drawing illustrated in  FIG. 7  uses, as a standard, a relative position of the forward traveling side tension wheel  35   a  and the rubber crawler  33  in the crawler width direction C in  FIG. 5A  (“Py 0 ” in  FIG. 7 ). An ordinate in  FIG. 7  illustrates a load that the forward traveling side tension wheel  35   a  receives from the inner surface of the rubber crawler  33  in the crawler thickness direction D (hereinafter, it is referred to as “a tension load received by the forward traveling side tension wheel  35   a ”). 
     More specifically, a range of “Py 0 ” to “Py 1 ” in the abscissa in  FIG. 7  corresponds to the stage from the state illustrated in  FIG. 5A  to the state illustrated in  FIG. 5B . A range of “Py 1 ” to “Py 3 ” in the abscissa of  FIG. 7  corresponds to the stage from the state illustrated in  FIG. 5B  through the state illustrated in  FIG. 5C  to the state that the forward traveling side tension wheel  35   a  completely overrides the core projection  41 . A range of “Py 3 ” to “Py 4 ” in the abscissa in  FIG. 7  corresponds to a state that the forward traveling side tension wheel  35   a  completely overrides the core projection  41  as illustrated in  FIG. 5D . 
     As illustrated in  FIG. 7 , the tension load received by the forward traveling side tension wheel  35   a  is substantially constant from the state illustrated in  FIG. 5A  to the state illustrated in  FIG. 5B  (see “F 1 ” of  FIG. 7 ). However, as illustrated in  FIG. 7 , when the forward traveling side tension wheel  35   a  is in the middle of overriding the side surface of the core projection  41 , the core projection  41  is sandwiched between the forward traveling side tension wheel  35   a  and the rubber crawler  33  (see  FIG. 6 ), so that the tension load received by the forward traveling side tension wheel  35   a  is made larger. As one example,  FIG. 7  illustrates an example that the tension load received by the forward traveling side tension wheel  35   a  increases just before the forward traveling side tension wheel  35   a  completely overrides the core projection  41  (“Py 2 ” to “Py 3 ” in the abscissa in  FIG. 7 ). However, there may be a case where such change of inclination does not exist. 
     Moreover, when the forward traveling side tension wheel  35   a  completely overrides the side surface of the core projection  41 , the tension load received by the forward traveling side tension wheel  35   a  becomes maximum. Next, while the forward traveling side tension wheel  35   a  moves on a top surface of the core projection  41  (“Py 3 ” to “Py 4 ” in the abscissa in  FIG. 7 ), the tension load received by the forward traveling side tension wheel  35   a  is substantially constant. If the forward traveling side tension wheel  35   a  is disengaged subsequently, as illustrated in a dashed line in  FIG. 7 , the tension load received by the forward traveling side tension wheel  35   a  is gradually reduced, and finally returns to the same as in the normal time. “Py 5 ” of the abscissa in  FIG. 7  illustrates a positional relationship at the time when the forward traveling side tension wheel  35   a  is completely disengaged to achieve a non-contact state of the forward traveling side tension wheel  35   a  and the core projection  41 . 
     In this way, the load tension received by the tension wheel  35  is largely fluctuated during the time that the tension wheel  35  is disengaged from the rubber crawler  33 . Consequently, disengagement of the tension wheel  35  from the rubber crawler  33  can be previously prevented by using the tension load information acquired by the sensor  34 . More specifically, in this embodiment, the control device  21  of the machine body  2  illustrated in  FIG. 1  compares the tension load information acquired by the sensor  34  with a predetermined threshold value. Moreover, the control device  21  executes processing in accordance with a comparison result with the predetermined threshold value. More specifically, the sensor  34  of this embodiment acquires, as the biasing load information, the pressure of the fluid element  51  in the cylinder  52  of the biasing body  50  which biases the forward traveling side tension wheel  35   a  to the rubber crawler  33 . In addition, when the pressure value acquired by the sensor  34  exceeds a predetermined threshold value, the control device  21  of this embodiment executes processing, including control such that the operator is notified and control such that the drive wheel  31  is stopped. 
     The predetermined threshold value may be, for example, a threshold value of the tension load information corresponding to the tension load received by the tension wheel  35  when the tension wheel  35  is in the middle of overriding the side surface of the core projection  41  (“F 2 ” of  FIG. 7 ). Due to this, the control device  21  can determine that the tension wheel  35  is in the middle of overriding the side surface of the core projection  41 . Further, as another predetermined threshold value, for example, a threshold value of the tension load information corresponding to the tension load received by the tension wheel  35  in a state that the tension wheel  35  completely overrides the side surface of the core projection  41  (“F 3 ” of  FIG. 7 ) may be used. In other words, as the predetermined threshold value, for example, a threshold value of the tension load information corresponding to both “F 2 ” and “F 3 ” in  FIG. 7  may be used. The sensor  34  is configured to be able to acquire the information corresponding to the tension load “F 2 ” received by the tension wheel  35  as the tension load information, and moreover, the information corresponding to the tension load “F 3 ” received by the tension wheel  35  as the tension load information. When the sensor  34  acquires the information corresponding to the tension load “F 2 ” and “F 3 ,” the control device  21  can determine that the tension wheel  35  completely overrides the side surface of the core projection  41  and is positioned on the top surface of the core projection  41 . A value to be used as the predetermined threshold value may be the tension load information corresponding to the tension load received by the tension wheel  35  at any position of “Py 1 ” to “Py 3 ” in the abscissa in  FIG. 7 . However, there is case that the tension wheel  35  slips down from the side surface of the core projection  41  in the middle of overriding the side surface of the core projection  41  and returns to a position of the normal time (see  FIG. 5A ). Consequently, to inhibit false detection of a sign of wheel-disengagement, the value to be used as the predetermined threshold value is preferably set to the tension load information corresponding to the tension load received by the tension wheel  35  at a position just before the tension wheel  35  completely overrides the side surface of the core projection  41 . 
     In this way, a situation that the tension wheel  35  overrides the core projection  41  can be detected when the predetermined threshold value is set to the tension load information corresponding to the tension load received by the tension wheel  35  and compared with an acquired value of the tension load information received by the sensor  34 . 
     As described above, the control device  21  executes the processing in accordance with the comparison result with the predetermined threshold value. The processing executed by the control device  21  is various processing which can previously prevent disengagement of the tension wheel  35  from the rubber crawler  33 . More specifically, the control device  21  may execute control regarding notification to the operator or the outside based on the comparison result. For example, the control device  21  allows the notification device  24  (see  FIG. 1 ) to notify the operator or the outside when the acquired value of the tension load information acquired by the sensor  34  reaches a predetermined threshold value corresponding to the tension load “F 2 ,” “F 3 ” received by the tension wheel  35  illustrated in  FIG. 7 . This allows the operator of the crawler traveling vehicle  1  also as the operator of the crawler traveling apparatus  3  to perceive the sign of disengagement of the tension wheel  35  from the rubber crawler  33 . 
     Further, the control device  21  may allow the notification device  24  to notify different notification information in accordance with the situation that the tension wheel  35  overrides the core projection  41 . For example, the control device  21  executes notification by a warning tone with a predetermined sound volume when it is determined that the tension wheel  35  is in the middle of overriding the side surface of the core projection  41  by the tension load information acquired by the sensor  34 . On the other hand, for example, the control device  21  may execute notification by a warning tone with a sound volume which is larger than the predetermined sound volume when it is determined that the tension wheel  35  is in a state of completely overriding the core projection  41  by the tension load information acquired by the sensor  34 . The different notification information is not particularly limited as long as it is information enabling a person to perceive a difference, not limited to the sound volume difference. 
     Also, the control device  21  may execute control regarding the drive of the drive wheel  31  based on the comparison result. For example, the control device  21  stops the drive of the drive wheel  31  by the drive device  23  when the tension load information in the crawler thickness direction D acquired by the sensor  34  reaches a predetermined threshold value corresponding to the tension load “F 3 ” received by the tension wheel  35  illustrated in  FIG. 7 . This prevents disengagement of the tension wheel  35  from the rubber crawler  33 . 
     Further, the control device  21  may select and execute any of the control regarding notification to the operator or the outside, and the control regarding the drive of the drive wheel  31  according to the comparison result. For example, the control device  21  executes only the control regarding notification to the operator or the outside when it is determined that the tension wheel  35  is in the middle of overriding the side surface of the core projection  41 . On the other hand, for example, the control device  21  executes stopping the drive of the drive wheel  31  when it is determined that the tension wheel  35  is in the state of completely overriding the core projection  41 . 
     As described above, according to the sensor  34  of the crawler traveling apparatus  3 , the tension load information in the crawler thickness direction D received by the tension wheel  35  from the inner surface of the rubber crawler  33  can be acquired. Moreover, by utilizing the tension load information acquired by the sensor  34 , the sign of disengagement of the tension wheel  35  from the rubber crawler  33  can be objectively determined. Consequently, the disengagement of the tension wheel  35  from the rubber crawler  33  can be previously prevented. 
     Also, the sensor  34  of this embodiment acquires the biasing load information received by the biasing body  50  from the tension wheel  35  as the tension load information. However, the tension load information acquired by the sensor  34  is not limited to the biasing load information, and any tension load information may be applied as long as it is the tension load information in the crawler thickness direction D that tension wheel  35  receives from the inner surface of the rubber crawler  33 . However, when there is the biasing body  50  which biases the tension wheel  35  to the inner surface of the rubber crawler  33  as in this embodiment, the biasing load information is preferably used as the tension load information. By doing this, the biasing load information can be easily acquired using an adjustment mechanism of the biasing force by the biasing body  50 , so that the tension load information can be easily acquired by the sensor  34 . 
     Especially, in a case where the biasing force of the biasing body  50  utilizes the fluid element  51  capable of compressive deformation, the sensor  34  preferably acquires the pressure of the fluid element  51  as the biasing load information. By doing this, the tension load information can be easily acquired by the sensor  34 . 
     Also, in a case where the fluid element  51  of the biasing body  50  is housed in the accommodation space  52   a  of the cylinder  52 , the sensor  34  preferably acquires the internal pressure of the fluid element  51  in the accommodation space  52   a . By doing this, the tension load information can be easily acquired by the sensor  34 . 
     The crawler traveling apparatus and the crawler traveling vehicle according to the present disclosure are not limited to a concrete configuration illustrated in the embodiment, and various modifications and changes can be executed without departing from the scope of the claims. In other words, based on the tension load information in the crawler thickness direction D that the tension wheel  35  receives from the inner surface of the rubber crawler  33 , the crawler monitoring method of monitoring disengagement of the tension wheel  35  from the rubber crawler  33 , the crawler traveling apparatus which executes the crawler monitoring method, and moreover, the crawler traveling vehicle and the crawler monitoring system belong to the technical scope of the present application. 
     More specifically, the crawler monitoring method according to the present disclosure is the crawler monitoring method of monitoring the disengagement of the tension wheel  35  from the rubber crawler  33  based on the load information related to the load that the tension wheel  35  receives from the endless rubber crawler  33  wound around the drive wheel  31  and the tension wheel  35 . More specifically, in this crawler monitoring method, the disengagement of the tension wheel  35  from the rubber crawler  33  is monitored based on, of the load information, the tension load information in the crawler thickness direction D that the tension wheel  35  receives from the inner surface of the rubber crawler  33 . 
     Also, the crawler monitoring system according to the present disclosure includes the crawler traveling apparatus  3  and the control device  21  which compares the tension load information acquired by the sensor  34  with the predetermined threshold value and executes processing in accordance with the comparison result. The crawler monitoring system according to the present disclosure further may include the notification device  24  capable of notifying the comparison result of the control device  21 . As an example of the processing in accordance with the comparison result, the control device  21  may control the notification information that the notification device  24  notifies the operator or the outside based on the comparison result. Also, as an example of the processing in accordance with the comparison result, the control device  21  of the crawler monitoring system according to the present disclosure may control the drive of the drive wheel  31  of the crawler traveling apparatus  3  based on the comparison result. 
     The crawler traveling vehicle  1  of the above-described embodiment has the configuration that the machine body  2  has the control device  21 . However, the control device  21  of the crawler monitoring system according to the present disclosure may be configured by an external apparatus positioned at an outer portion of the crawler traveling vehicle  1 . For example, the control device  21  of the crawler monitoring system may be provided to a server as the external apparatus positioned at the outer portion of the crawler traveling vehicle  1 . Further, the crawler monitoring system may include the operating device  22 , the notification device  24  and the pressure adjusting device  25 . Also, the crawler monitoring system further may include other devices such as the communication device. The operating device  22 , the notification device  24 , the pressure adjusting device  25  and other devices in the crawler monitoring system may be configured by the external apparatus positioned at the outer portion of the crawler traveling vehicle  1  in the same manner as the control device  21 . The control device  21 , the operating device  22 , the notification device  24 , the pressure adjusting device  25  and other devices may be respectively provided to different external apparatuses. 
     Also, while the crawler traveling vehicle  1  of the above-described embodiment has the configuration that the machine body  2  includes the control device  21  and the notification device  24 , for example, it may have the configuration that the crawler traveling apparatus  3  includes the control device  21  and the notification device  24 . Moreover, the crawler traveling apparatus  3  may include other devices. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure relates to the crawler traveling apparatus, the crawler monitoring system, the crawler traveling vehicle and the crawler monitoring method.