Patent Publication Number: US-2023132970-A1

Title: Electric Tractor

Description:
TECHNICAL FIELD 
     The present invention relates to a configuration for supporting various devices in an electric tractor. 
     BACKGROUND ART 
     Patent Document 1 discloses a tractor as an electric work vehicle. This tractor is so configured that a battery and a motor are installed in place of an engine. The battery is housed in a sealed state by a battery cover. The outer wall face of the battery cover forms a part of the tractor&#39;s exterior. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-000957 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The configuration in the Patent Document 1 does not disclose the specific configuration of how the various devices of the electric tractor are supported. Therefore, there remained room for improvement in terms of efficient use of space, etc. 
     The present invention has been made in view of the above circumstances, and one object thereof is to realize a strong structure to support the battery in the electric tractor. 
     MEANS FOR SOLVING THE PROBLEMS AND EFFECT 
     The problem to be solved by the present invention is as above, and the means for solving the problem and effects by the means are described below. 
     According to a first aspect of the present invention, there is provided an electric tractor having the following configuration. That is, this electric tractor is equipped with a battery, a transmission unit, a machine body frame, a rear axle unit, and a front axle unit. The transmission unit changes the speed of the input power and outputs the power. The machine body frame is fixed to the transmission unit. The rear axle unit supports rear wheels, and transmits, to the rear wheels, the power output from the transmission unit. The front axle unit supports front wheels. The rear axle unit and the front axle unit support chassis, which is configured to include the machine body frame and the transmission unit. The battery is supported by the chassis. 
     This allows for a strong support configuration that, in an electric tractor, supports the weight of the battery and the like. 
     The electric tractor preferably has the following configuration. That is, the electric tractor is equipped with a plate-shaped base member and a vibration-proof member. Without a vibration, the vibration-proof member allows the base member to be supported with respect to the machine body frame. The battery is fixed to the base member. 
     This allows the support configuration of the battery to be realized in a simplified configuration using the plate-shaped multi-purpose plate. 
     The electric tractor preferably has the following configuration. That is, the electric tractor is equipped with an on-board charging unit, a cooling unit, an electronic control unit (ECU), an inverter, and a terminal box. The on-board charging unit controls the charging of the battery. The cooling unit cools the battery. The ECU controls the battery. The inverter controls the rotation speed of the motor connected to the battery. The terminal box relays electricity. When the base member is separated from the machine body frame; in addition to the battery, at least one of the on-board charging unit, the cooling unit, the ECU, the inverter, and terminal box are placed on the base member side. 
     This makes it possible to realize, for electric-related units, a unitization that is based on the base member, and to place the unit in a travel machine body. Therefore, the tractor is easy to handle during manufacturing, etc. 
     In the above electric tractor described, the battery is preferably placed above an axle of the front wheels. 
     This allows the minimum ground height of the electric tractor to be easily secured. 
     In the electric tractor, the on-board charging unit that controls the charging of the battery is preferably placed above the battery. 
     This allows for a compact placement that includes the battery and the on-board charging unit. 
     According to a second aspect of the present invention, there is provided an electric tractor having the following configuration. That is, this electric tractor is equipped with a machine body frame, a battery, a travel motor, and a transmission unit. The travel motor is an electric motor that generates power to run a travel machine body. The transmission unit is placed in a more rearward portion of the travel machine body than the battery, in plan view. The machine body frame is equipped with frame members placed in pairs on right and left. In plan view, the travel motor is placed behind the battery and in front of the transmission unit, and is placed between the right and left frame members. 
     This allows for a strong support configuration that, in an electric tractor, supports the weight of the battery and the like. In addition, since the travel motor is placed behind the battery, it is easy to omit or shorten of a drive shaft between the travel motor and the more rearward transmission unit. In addition, since the travel motor is placed closer to the rear, a space where members can be placed can be obtained between the battery and the travel motor in plan view. Further, since the travel motor is placed between the left and right frame members, a compact configuration can be realized. 
     According to a third aspect of the present invention, there is provided an electric tractor having the following configuration. That is, this electric tractor is equipped with a machine body frame, a hydraulic pump, and a pump motor. The pump motor is an electric motor that generates power to drive the hydraulic pump. The machine body frame is equipped with frame members placed in pairs on right and left. At least a part of the pump motor is positioned outside the frame member in the left/right direction of a travel machine body. 
     This allows the pump motor to be compactly placed in a position that does not interfere with a surrounding member. 
     The electric tractor preferably has the following configuration. That is, this electric tractor is equipped with a pump inverter to control the rotation speed of the pump motor. At least a part of the pump inverter is positioned on the opposite side of the pump motor on right and left, and outside the frame member in the left/right direction. 
     This allows the pump inverter to be compactly placed in a position that does not interfere with a surrounding member. In addition, the pump motor and the pump inverter are placed separately on the right and left sides of the machine body frame, making it possible to improve the balance of the travel machine body. 
     According to a fourth aspect of the present invention, there is provided an electric tractor having the following configuration. That is, this electric tractor is equipped with a machine body frame and a pump inverter. The pump inverter controls the rotation speed of the electric motor. The machine body frame is equipped with frame members placed in pairs on right and left. At least a part of the pump inverter is placed outside the frame member in the left/right direction. 
     This allows the pump inverter to be compactly placed in a position that does not interfere with a surrounding member. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a side view of an overall configuration of an electric tractor according to one embodiment of the present invention. 
         FIG.  2    is a perspective view showing chassis with which the electric tractor is equipped. 
         FIG.  3    is a perspective view showing inside of a hood of an electric tractor of another configuration. 
         FIG.  4    a perspective view showing the inside of the hood from a viewpoint different from that of  FIG.  3   . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, embodiments of the present invention are described with reference to the drawings.  FIG.  1    is a side view of an electric tractor  1  according to one embodiment of the present invention. 
     The electric tractor  1  shown in  FIG.  1    is configured as an agricultural tractor. The electric tractor  1  is equipped with a travel machine body  2  as a body portion that can travel in a farm field. 
     A work instrument  3  can be connected to the travel machine body  2 . The work instruments  3  include, for example, a cultivator (management machine), a plow, a fertilizer, a mower, and a seeding machine. Various types of work instruments  3  can be mounted to the travel machine body  2  as needed. 
     The front portion of the travel machine body  2  of the electric tractor  1  is supported by a pair of right and left front wheels  7 , and the rear portion of the travel machine body  2  is supported by a pair of right and left rear wheels  8 . 
     Chassis  20 , which is a strength member of the electric tractor  1 , is placed at the bottom portion of the travel machine body  2 . The chassis  20  includes a transmission unit  21 &#39;s housing  22 , and a machine body frame  30 . 
     Inside the transmission unit  21 , there is placed a transmission mechanism including, for example, a gear train. The transmission unit  21  changes the speed of the power input from a travel motor  41  described below. The power shifted in the transmission unit  21  is transmitted to a front axle unit  51  and a rear axle unit  52 . 
     The transmission unit  21  has the housing  22  that houses the transmission mechanism. The housing  22  is made of cast metal, for example. The housing  22  of the transmission unit  21  has high mechanical rigidity, and therefore is used as a part of the chassis  20 . 
     As shown in  FIG.  2   , the machine body frame  30  includes frame members  31 ,  32  which are placed in pairs on left and right. Each of the two frame members  31 ,  32  is formed as a plate, and so is placed that its thickness direction is along the left/right direction of the travel machine body  2 . A proper interval is formed between the two frame members  31 ,  32 . 
     The rear end portions of the respective frame members  31 ,  32  are fixed to the transmission unit  21 . The frame members  31 ,  32  extend forward in a generally horizontal direction from their portions for coupling with the transmission unit  21 . Each of the frame members  31 ,  32  is composed of a plurality of plate-like members connected in the front-back direction. 
     The two frame members  31 ,  32  are placed parallel to each other. As shown in  FIG.  2   , the machine body frame  30  is equipped with a plurality of members including connecting members  33 ,  34 ,  35 . The connecting members  33 ,  34 ,  35  are so placed as to extend in the left/right direction, and connect the two frame members  31 ,  32  to each other. This increases mechanical rigidity of the machine body frame  30 . 
     A front axle unit  51  is connected to the machine body frame  30  with which the chassis  20  is equipped. The front axle unit  51  supports the weight of the front portion of the chassis  20 . The front wheels  7  shown in  FIG.  1    are rotatably supported at both ends of the front axle unit  51  in a vehicle width direction. The travel machine body  2  is equipped with a transmission shaft  27  shown in  FIG.  2   . The transmission shaft  27  connects the front axle unit  51  with the transmission unit  21 . To the front axle unit  51 , power is input from the transmission unit  21  via the transmission shaft  27 . The front axle unit  51  transmits the input power to the front wheels  7 . As a result, the front wheels  7  are driven. 
     The rear axle unit  52  is placed in pairs on right and left in a manner to sandwich the housing  22  of transmission unit  21 . Each of the rear axle units  52  is secured to a side of the housing  22  of the transmission unit  21 . The rear axle unit  52  supports the weight of the rear portion of the chassis  20 . In each of the rear axle units  52 , the rear wheel  8  shown in  FIG.  1    is rotatably supported at the outer end portions of the vehicle in the vehicle width direction. To the rear wheel  8 , the rear axle unit  52  transmits the power input from the transmission unit  21 . As a result, the rear wheels  8  are driven. 
     A hood  9  is placed at the front portion of the travel machine body  2 . A battery  15  is housed inside the hood  9 . The battery  15  supplies power to a plurality of electric motors that drives the electric tractor  1 . The configuration of the battery  15  is optional, and can be, for example, a lithium-ion secondary battery. The battery  15  is so fixed as to be placed on the machine body frame  30 . Thus, the battery  15  is positioned higher than an axle  7   a  of the front wheel  7 . 
     In the interior space of the hood  9 , there is provided an on-board charging unit  16  above the battery  15 . The on-board charging unit  16  can, for example, convert a household AC power voltage to a DC voltage, making it possible to charge the battery  15 . 
     In the interior space of the hood  9 , there is provided a BMS unit  17  in front of the battery  15 . BMS is an abbreviation for Battery Management System. The BMS unit  17  is configured as a computer, and is a type of ECU. The BMS unit  17  has a function of monitoring the voltage, temperature, etc. of the battery  15  and thereby detecting an abnormality. The BMS unit  17  also estimates the remaining battery capacity of the battery  15 , and outputs the obtained information to the on-board charging unit  16 . This prevents overcharging of the battery  15 . 
     Behind the hood  9 , there is provided an operator seat  13  on which the operator can be seated. A plurality of human operator-operated members are placed near the operator seat  13 . The operated member is, for example, a steering wheel  12  placed in front of the operator seat  13 . Although details are omitted, the operated members include, in addition to the steering wheel  12 , a main gear shift lever, an auxiliary gear shift lever, a PTO (power take off) gear shift lever, a hydraulic operation switch, and hydraulic operation lever, etc. 
     Below the operator seat  13 , there is placed the above transmission unit  21 . To the front end portion of the housing  22  of the transmission unit  21 , a housing  42  of the travel motor  41  is fixed. The travel motor  41  is configured as an electric motor, and its output shaft, though not shown, is directed toward the front and rear of the travel machine body  2 . The output shaft of the travel motor  41  protrudes rearward from the housing  42 , and is connected to an input shaft of the transmission unit  21 . 
     A known 3-point link mechanism  25  is equipped at the rear portion of the travel machine body  2 , and the work instrument  3  can be connected to the travel machine body  2  via the 3-point link mechanism  25 . A lifting/lowering actuator  26  is placed near the 3-point link mechanism  25 . The lifting/lowering actuator  26  includes, for example, a hydraulic cylinder. Driving the lifting/lowering actuator  26  can adjust the height and posture of the work instrument  3  mounted on the travel machine body  2 . 
     As shown in  FIG.  2   , a hydraulic pump  43  to supply hydraulic oil to various hydraulic units is mounted on the chassis  20 . The hydraulic units as objects to which hydraulic oil is supplied may include, but are not limited to, for example, the lifting/lowering actuator  26  and a hydraulic steering unit (not shown). Of the one-side frame member  31  that constitutes the machine body frame  30 , the hydraulic pump  43  is fixed to the face that faces inside in the vehicle width direction. Although not shown, a drive input shaft of the hydraulic pump  43  is oriented along the width direction of the travel machine body  2 . 
     A pump motor  44  to drive the hydraulic pump  43  is mounted on the chassis  20 . The pump motor  44  is configured as an electric motor. The pump motor  44  is so placed as to be in line with the hydraulic pump  43  in the width direction of the travel machine body  2 . 
     The pump motor  44  is fixed to the frame member  31 &#39;s face that faces outside in the width direction of the travel machine body  2 . In other words, the pump motor  44  is placed on the opposite side of the hydraulic pump  43 , sandwiching therebetween the frame member  31 . Thus, a housing of the pump motor  44  is positioned outside the machine body frame  30  in the width direction of the travel machine body  2 . 
     Although not shown, the output shaft of the pump motor  44  is oriented along the width direction of the travel machine body  2 . The output shaft of the pump motor  44  protrudes through the frame member  31  toward the center side of the travel machine body  2 , and is connected to the drive input shaft of the hydraulic pump  43 . 
     A pump inverter  45  to change the rotation speed of the pump motor  44  is mounted on the machine body frame  30 . The pump inverter  45  is placed in line with the hydraulic pump  43  and the pump motor  44  substantially in the width direction of the travel machine body  2 . 
     Of the pair of left and right frame members  31 ,  32  included in the machine body frame  30 , the pump inverter  45  is fixed to frame members  32  on the opposite side of the frame member  31  to which the pump motor  44  is mounted. The pump inverter  45  is fixed to the frame member  32 &#39;s face that faces outside in the width direction of the travel machine body  2 . Therefore, the pump inverter  45  is placed outward on the opposite side of the pump motor  44  in the width direction of the travel machine body  2 , more than the machine body frame  30 . 
     The above layout allows the hydraulic pump  43 , the pump motor  44 , and the pump inverter  45  to be preferably supported by the chassis  20 . To the machine body frame  30 , the pump motor  44  is placed on one side in the width direction of the travel machine body  2 , and the pump inverter  45  is placed on the opposite side, thus making it easy to secure the balance of the travel machine body  2 . 
     A PTO shaft, not shown, is placed at the travel machine body  2 . The PTO shaft is connected to the drive input shaft of the work instrument  3 . To drive the PTO shaft, a PTO drive motor (not shown) is installed at a proper position of the travel machine body  2 . The PTO drive motor is configured as an electric motor. The PTO drive motor can drive the work instrument  3  via the PTO shaft. 
     The electric tractor  1  according to the present embodiment is equipped with the travel motor  41  as a drive source for running the travel machine body  2 . Meanwhile, as a variation of the tractor specification, the tractor could be configured with the chassis  20  kept common, and with an engine placed instead of the electric motor. 
     Suppose that in the engine specification, a housing for the engine and clutch is used as part of the chassis. In this configuration; at the time of attempting to change to the electric motor specification, the chassis is not strong enough because of the loss of the housing as the strength member. Therefore, it is difficult to share the chassis between the two specifications. 
     In this respect; in the chassis  20  of the present embodiment, the machine body frame  30 , which includes a pair of plate-shaped members, extends from the transmission unit  21  to the vicinity of the front end of the travel machine body  2 . In other words, a middle portion of the machine body frame  30  is not interrupted. It is suggested that, when this chassis  20  is applied to the engine specification, the engine is mounted in the space where the battery  15  was mounted in the hood  9 . Thus, when the chassis  20  of the configuration of the present embodiment is shared between the electric motor specification and the engine specification, the mechanical strength can be easily secured regardless of which specification is used. 
     In the present embodiment, the travel motor  41  is so placed to the transmission unit  21  as to be in close proximity at the front side. In the present embodiment, the housing  42  of the travel motor  41  is directly secured to the front portion of the housing  22  of the transmission unit  21 . At least a part of the housing  42  is so placed as to be inserted between the left and right frame members  31 ,  32 . 
     This layout makes it possible to directly connect the output shaft of the travel motor  41  with the input shaft of the transmission unit  21 . Thus, the drive shaft connecting both is omitted. However, the output shaft of the travel motor  41  may be connected with the input shaft of the transmission unit  21  via a short drive shaft that is not exposed to the outside. 
     This direct layout allows the travel motor  41  to be placed closer to the rear, and, as shown in  FIG.  2   , a proper space Si can be secured between the battery  15  and the travel motor  41  and between the left and right frame members  31 ,  32 , in plan view. In the present embodiment, the hydraulic pump  43  and a hydraulic piping  46  that leads the hydraulic oil are placed in this space Si. Thus, effectively utilizing the space Si can compactly place the hydraulic pump  43 , etc. 
     As described above, the electric tractor  1  of the present embodiment is equipped with the battery  15 , the transmission unit  21 , the machine body frame  30 , the rear axle unit  52 , and the front axle unit  51 . The transmission unit  21  shifts the input power and outputs the shifted input power. The machine body frame  30  is fixed to the transmission unit  21 . The rear axle unit  52  supports the rear wheels  8 , and transmits, to the rear wheels  8 , the power output from the transmission unit  21 . The front axle unit  51  supports the front wheels  7 . The rear axle unit  52  and the front axle unit  51  support the chassis  20 . The chassis  20  includes the machine body frame  30  and the transmission unit  21 . The battery  15  is supported by the chassis  20 . 
     This enables the electric tractor  1  to have a strong support configuration that supports the weight of the battery  15  and the like. 
     In the electric tractor  1  of the present embodiment, the battery  15  is placed above the axle of the front wheels  7 . 
     This allows the minimum ground height of the electric tractor  1  to be easily secured. 
     In the electric tractor  1  of the present embodiment, the on-board charging unit  16  that controls the charging of the battery  15  is placed above the battery  15 . 
     This allows for a compact placement that includes the battery  15  and the on-board charging unit  16 . 
     The electric tractor  1  of the present embodiment is also equipped with the machine body frame  30 , the battery  15 , the travel motor  41 , and the transmission unit  21 . The travel motor  41  is an electric motor that generates power to run the travel machine body  2 . The transmission unit  21  is placed in a more rearward portion of the travel machine body  2  than the battery  15 , in plan view. The machine body frame  30  has the frame members  31 ,  32  placed in pairs on left and right. The travel motor  41  is placed behind the battery  15  and in front of the transmission unit  21  in plan view, and is placed between the left and right frame members  31 ,  32 . 
     This enables the electric tractor  1  to have a strong support configuration that supports the weight of the battery  15  and the like. In addition, since the travel motor  41  is placed behind the battery  15 , it is easy to omit or shorten the drive shaft between the travel motor  41  and the more rearward transmission unit  21 . Since the travel motor  41  is placed closer to the rear, the space where members can be placed can be obtained between the battery  15  and the travel motor  41  in plan view. Since the travel motor  41  is placed between the left and right frame members  31 ,  32 , a compact configuration can be realized. 
     The electric tractor  1  of the present embodiment is equipped with the machine body frame  30 , the hydraulic pump  43 , and the pump motor  44 . The pump motor  44  is an electric motor that generates power to drive the hydraulic pump  43 . The machine body frame  30  is equipped with the frame members  31 ,  32  placed in pairs on left and right. At least a part of the pump motor  44  is positioned outside the frame members  31 ,  32  in the left/right direction of the travel machine body  2 . 
     This allows the pump motor  44  to be compactly placed in the position that does not interfere with a surrounding member. 
     The electric tractor  1  of the present embodiment is equipped with the pump inverter  45  to control the rotation speed of the pump motor  44 . At least a part of the pump inverter  45  is positioned on the opposite side of the pump motor  44  on right and left, and the outside the frame members  31 ,  32  in the right/left direction. 
     This allows the pump inverter  45  to be compactly placed in the position that does not interfere with a surrounding member. 
     The electric tractor  1  of the present embodiment is equipped with the machine body frame  30  and the pump inverter  45 . The pump inverter  45  controls the rotation speed of the pump motor  44  which is an electric motor. The machine body frame  30  is equipped with the frame members  31 ,  32  placed in pairs on left and right. At least a part of the pump inverter  45  is placed outside the frame members  31 ,  32  in the left/right direction. 
     This allows the pump inverter  45  to be compactly placed in a position that does not interfere with a surrounding member and to be firmly supported by the machine body frame  30 . 
     Referring now to  FIGS.  3  and  4   , another configuration for supporting the battery  15  and the like at the front portion of the travel machine body  2  is to be described. In the following description, parts identical with or similar to those of the above embodiment are marked with the same symbols in the drawings, and a description thereof will be omitted as the case may be. 
     In the electric tractor  1  shown in  FIGS.  3  and  4   , a multi-purpose plate (base member)  61  is placed above the front portion of the machine body frame  30 . The multi-purpose plate  61  is a horizontal plate-like member. The multi-purpose plate  61  is so placed as to straddle the pair of frame members  31 ,  32  with which the machine body frame  30  is equipped. 
     The two frame members  31 ,  32  each have two brackets extending outward on the left and right. A vibration-proof member  62  is mounted to each bracket. Each of the vibration-proof members  62  includes a member capable of cushioning an impact, e.g., rubber. The four vibration-proof members  62  support the lower face of the multi-purpose plate  61 . This allows the multi-purpose plate  61  to be supported with respect to the machine body frame  30  free from a vibration. 
     The above battery  15  is placed on the upper face of the multi-purpose plate  61 . The battery  15  is fixed to the multi-purpose plate  61  by a plurality of fixing blocks  63  and the like. To increase rigidity, convex portions that protrude upward or downward may be formed on the multi-purpose plate  61 . 
     On the upper side of the multi-purpose plate  61 , there is provided a support frame  64 . The support frame  64  is composed of a combination of a plurality of linearly elongated members. The support frame  64  is so placed as to surround the battery  15 . The support frame  64  is fixed to the upper face of the multi-purpose plate  61 . 
     The on-board charging unit  16  is fixed to the upper face of the battery  15 . The BMS unit  17  is fixed to the front face of the battery  15 . 
     A terminal box  18  is placed in front of the on-board charging unit  16 . The terminal box  18  is fixed to the upper portion of the support frame  64 . A plurality of wires, not shown in the figure, are connected to the terminal box  18 . The terminal box  18  relays electricity, for example, across the battery  15  and an inverter  19 . 
     The inverter  19  is fixed to the lower face of the multi-purpose plate  61 . The inverter  19  controls the rotation speed of the travel motor  41 . The inverter  19  is so supported by the multi-purpose plate  61  as to be suspended down. At the front end portion of the machine body frame  30 , the inverter  19  is placed between the pair of left and right frame members  31 ,  32 . 
     A cooling fan (cooling unit)  38  is placed on one of the right and left sides of the battery  15 . The battery  15  has a water cooling system, not shown in the figure, for cooling. The cooling fan  38  blows air toward a radiator with which the water cooling system is equipped. 
     Thus, in the example shown in  FIGS.  3  and  4   , an electric unit including the battery  15 , the on-board charging unit  16 , the BMS unit  17 , the terminal box  18 , the inverter  19 , and the cooling fan  38  are placed on the multi-purpose plate  61  placed above the machine body frame  30 . 
     Therefore, when the multi-purpose plate  61  is removed from the machine body frame  30 , the battery  15 , the on-board charging unit  16 , the BMS unit  17 , the terminal box  18 , the inverter  19 , and the cooling fan  38  are positioned on the multi-purpose plate  61  side. Since the electric unit can be built in this way with the multi-purpose plate  61  as the base member, it is easy to share the chassis  20  with the above engine specification. It also facilitates the manufacture of tractors with the electric motor specifications. 
     As described above, the electric tractor  1  is equipped with the plate-shaped multi-purpose plate  61  and the vibration-proof member  62 . Without a vibration, the vibration-proof member  62  allows the multi-purpose plate  61  to be supported with respect to the machine body frame  30 . The battery  15  is fixed to multi-purpose plate  61 . 
     This allows the support configuration of the battery  15  to be realized in a simplified configuration using the plate-shaped multi-purpose plate  61 . 
     The electric tractor  1  of the present embodiment also includes the on-board charging unit  16 , the cooling fan  38 , the BMS unit  17 , the inverter  19 , and the terminal box  18 . The on-board charging unit  16  controls the charging of the battery  15 . The cooling fan  38  cools the battery  15 . The BMS unit  17  controls the battery  15 . The inverter  19  controls the rotation speed of the travel motor  41  connected to the battery  15 . The terminal box  18  relays electricity. When the multi-purpose plate  61  is separated from the machine body frame  30 ; in addition to the battery  15 , the on-board charging unit  16 , the cooling fan  38 , the BMS unit  17 , the inverter  19 , and the terminal box  18  are placed on the multi-purpose plate  61  side. 
     This makes it possible to realize, for electric-related units, a unitization that is based on the multi-purpose plate  61 , and to place the unit in the travel machine body  2 . Therefore, the electric tractor  1  is easy to handle during manufacturing, etc. 
     Although the preferred embodiment of the present invention has been described above, the above configurations can be modified as follows. 
     In the configurations shown in  FIGS.  1  and  2   , the lower face of the battery  15  is substantially the same in height as the upper face of the machine body frame  30 . Meanwhile, the lower portion of the battery  15  may be so placed as to be inserted between the two frame members  31 ,  32 . The lower end of the battery  15  may be placed in a position lower than the axle  7   a  of the front wheels  7 . 
     Not limited to the on-board charging unit  16 , various components (e.g., an electric part such as harness connector) can be placed above the battery  15 . 
     The placement of the battery  15 , on-board charging unit  16 , and BMS unit  17  in the inner portion of the hood  9  is optional. For example, both the on-board charging unit  16  and the BMS unit  17  can be placed above the battery  15 . 
     The BMS unit  17  may be placed above the battery  15 , and the on-board charging unit  16  may be placed in front of the battery  15 . 
     In the configurations shown in  FIGS.  3  and  4    as well, placing of the on-board charging unit  16 , the BMS unit  17 , the terminal box  18 , the inverter  19 , and the cooling fan  38  can be changed as needed. For example, at least one of the on-board charging unit  16 , the BMS unit  17 , the terminal box  18 , and the cooling fan  38  can be placed below the multi-purpose plate  61 . The inverter  19  can be placed above the multi-purpose plate  61 . 
     The pump motor  44  may be placed entirely outside the machine body frame  30  on right and left, or only partially outside the machine body frame  30  on right and left. The same applies to the pump inverter  45 . 
     The position of the pump inverter  45  is optional; for example, the pump inverter  45  can be placed at the front end portion of the machine body frame  30 . 
     The cooling fan  38  shown in  FIG.  3    can be so modified as to simply blow air onto and cool the battery  15 , instead of blowing air onto the radiator in the water cooling method. 
     In the configurations shown in  FIGS.  3  and  4   , at least one of the on-board charging unit  16 , the BMS unit  17 , the terminal box  18 , the inverter  19 , etc., can be mounted on the machine body frame  30  side instead of the multi-purpose plate  61  side. 
     The placement of the pump motor  44  and pump inverter  45  shown in  FIGS.  1  and  2   , can be applied to the configuration having the multi-purpose plate  61  as shown in  FIGS.  3  and  4   . 
     REFERENCE SIGNS LIST 
     
         
           1 : electric tractor 
           7 : front wheel 
           7   a : axle of front wheel 
           8 : rear wheel 
           15 : battery 
           16 : on-board charging unit 
           17 : BMS unit (ECU) 
           18 : terminal box 
           19 : inverter 
           20 : chassis 
           21 : transmission unit 
           30 : machine body frame 
           31 : frame member 
           32 : frame member 
           38 : cooling fan (cooling unit) 
           41 : travel motor 
           43 : hydraulic pump 
           44 : pump motor (electric motor) 
           45 : pump inverter 
           51 : front axle unit 
           52 : rear axle unit 
           61 : multi-purpose plate (base member) 
           62 : vibration-proof member